Electronics and Electrical Advanced Mcqs

Multiple Choice Questions and Answers on Semiconductor
Theory
Q1. A semiconductor is formed by ……… bonds.
1. Covalent
2. Electrovalent
3. Co-ordinate
4. None of the above
Answer : 1
Q2. A semiconductor has ………… temperature coefficient of
resistance.
1. Positive
2. Zero
3. Negative
Answer : 3
Q3. The most commonly used semiconductor is ………..
1. Germanium
2. Silicon
3. Carbon
4. Sulphur
Answer : 2
Q4. A semiconductor has generally ……………… valence
electrons.
1. 2
2. 3
3. 6
4. 4
Answer : 4
Q5. The resistivity of pure germanium under standard
conditions is about ……….
1. 6 x 104
2. Ω cm
3. 60
4. Ω cm
5. 3 x 106
6. Ω cm
7. 6 x 10-4
8. Ω cm
Answer : 2
Q6. The resistivity of a pure silicon is about ……………
1. 100 Ω cm
2. 6000 Ω cm
3. 3 x 105 Ω m
4. 6 x 10-8 Ω cm
Answer : 2
Q7. When a pure semiconductor is heated, its resistance
…………..
1. Goes up
2. Goes down
3. Remains the same
4. Can’t say
Answer : 2
Q8. The strength of a semiconductor crystal comes from ……..
1. Forces between nuclei
2. Forces between protons
3. Electron-pair bonds
Answer : 3
Q9. When a pentavalent impurity is added to a pure
semiconductor, it becomes ………
1. An insulator
2. An intrinsic semiconductor
3. p-type semiconductor
4. n-type semiconductor
Answer : 4
Q10. Addition of pentavalent impurity to a semiconductor
creates many ……..
1. Free electrons
2. Holes
3. Valence electrons
4. Bound electrons
Answer : 1
Q11. A pentavalent impurity has ………. Valence electrons
1. 3
2. 5
3. 4
4. 6
Answer : 2
A12. An n-type semiconductor is ………
1. Positively charged
2. Negatively charged
3. Electrically neutral
Answer : 3
Q13. A trivalent impurity has ….. valence electrons
1. 4
2. 5
3. 6
4. 3
Answer : D4
A14. Addition of trivalent impurity to a semiconductor creates
many ……..
1. Holes
2. Free electrons
3. Valence electrons
4. Bound electrons
Answer : 1
Q15. A hole in a semiconductor is defined as …………….
1. A free electron
2. The incomplete part of an electron pair bond
3. A free proton
4. A free neutron
Answer : 2
Q16. The impurity level in an extrinsic semiconductor is about
….. of pure semiconductor.
1. 10 atoms for 108 atoms
2. 1 atom for 108 atoms
Answer : 2
Q17. As the doping to a pure semiconductor increases, the bulk
resistance of the semiconductor ………..
1. Remains the same
2. Increases
3. Decreases
Answer : 3
Q18. A hole and electron in close proximity would tend to
……….
1. Repel each other
2. Attract each other
3. Have no effect on each other
Answer : 2
Q19. In a semiconductor, current conduction is due to ……..
1. Only holes
2. Only free electrons
3. Holes and free electrons
Answer : 3
Q20. The random motion of holes and free electrons due to
thermal agitation is called ……….
1. Diffusion
2. Pressure
3. Ionisation
Answer : 1
Q21. A forward biased pn junction diode has a resistance of
the order of
1. Ω
2. kΩ
3. MΩ
Answer : 1
Q22. The battery connections required to forward bias a pn
junction are ……
1. +ve terminal to p and –ve terminal to n
2. -ve terminal to p and +ve terminal to n
3. -ve terminal to p and –ve terminal to n
Answer : 1
Q23. The barrier voltage at a pn junction for germanium is
about ………
3. 5 V
4. 3 V
5. Zero
6. 3 V
Answer : 4
Q24. In the depletion region of a pn junction, there is a
shortage of ……..
1. Acceptor ions
2. Holes and electrons
3. Donor ions
Answer : 2
Q25. A reverse bias pn junction has …………
1. Very narrow depletion layer
2. Almost no current
3. Very low resistance
4. Large current flow
Answer : 2
Q26. A pn junction acts as a ……….
1. Controlled switch
2. Bidirectional switch
3. Unidirectional switch
Answer : 3
Q27. A reverse biased pn junction has resistance of the order
of
1. Ω
2. kΩ
3. MΩ
Answer : 3
Q28. The leakage current across a pn junction is due to
…………..
1. Minority carriers
2. Majority carriers
3. Junction capacitance
Answer : 1
Q29. When the temperature of an extrinsic semiconductor is
increased, the pronounced effect is on……
1. Junction capacitance
2. Minority carriers
3. Majority carriers
Answer : 2
Q30. With forward bias to a pn junction , the width of
depletion layer ………
1. Decreases
2. Increases
3. Remains the same
Answer : 1
Q31. The leakage current in a pn junction is of the order of
1. Aa
2. mA
3. kA
4. µA
Answer : 4
Q32. In an intrinsic semiconductor, the number of free
electrons ………
1. Equals the number of holes
2. Is greater than the number of holes
3. Is less than the number of holes
Answer : 1
Q33. At room temperature, an intrinsic semiconductor has
……….
1. Many holes only
2. A few free electrons and holes
3. Many free electrons only
4. No holes or free electrons
Answer : 2
Q34. At absolute temperature, an intrinsic semiconductor has
……….
1. A few free electrons
2. Many holes
3. Many free electrons
4. No holes or free electrons
Answer : 4
Q35. At room temperature, an intrinsic silicon crystal acts
approximately as ……
1. A battery
2. A conductor
3. An insulator
4. A piece of copper wire
Answer : 3
Multiple Choice Questions and Answers on Semiconductor
Diode
Q1. A crystal diode has ………
1. one pn junction
2. two pn junctions
3. three pn junctions
4. none of the above
Answer : 1
Q2. A crystal diode has forward resistance of the order of
……………
1. kΩ
2. Ω
3. MΩ
Answer : 2
Q3. If the arrow of crystal diode symbol is positive w.r.t. bar,
then diode is ………….. biased.
1. forward
2. reverse
3. either forward or reverse
Answer : 1
Q4. The reverse current in a diode is of the order of
……………….
1. kA
2. mA
3. μA
4. A
Answer : 3
Q5. The forward voltage drop across a silicon diode is about
…………………
1. 2.5 V
2. 3 V
3. 10 V
4. 0.7 V
Answer : 4
Q6. A crystal diode is used as ……………
1. an amplifier
2. a rectifier
3. an oscillator
4. a voltage regulator
Answer : 2
Q7. The d.c. resistance of a crystal diode is ………….. its a.c.
resistance
1. the same as
2. more than
3. less than
Answer : 3
Q8. An ideal crystal diode is one which behaves as a perfect
……….. when forward biased.
1. conductor
2. insulator
3. resistance material
Answer : 1
Q9. The ratio of reverse resistance and forward resistance of a
germanium crystal diode is about ………….
1. 1 : 1
2. 100 : 1
3. 1000 : 1
4. 40,000 : 1
Answer : 4
Q 10. The leakage current in a crystal diode is due to
…………….
1. minority carriers
2. majority carriers
3. junction capacitance
Answer :1
Q11. If the temperature of a crystal diode increases, then
leakage current ………..
1. remains the same
2. decreases
3. increases
4. becomes zero
Answer :3
Q12. The PIV rating of a crystal diode is ………….. that of
equivalent vacuum diode
1. the same as
2. lower than
3. more than
Answer :2
Q13. If the doping level of a crystal diode is increased, the
breakdown voltage………….
1. remains the same
2. is increased
3. is decreased
Answer :3
Q14. The knee voltage of a crystal diode is approximately
equal to ………….
1. applied voltage
2. breakdown voltage
3. forward voltage
4. barrier potential
Answer :4
Q15. When the graph between current through and voltage
across a device is a straight line, the device is referred to as
……………….
1. linear
2. active
3. nonlinear
4. passive
Answer :1
Q16. When the crystal current diode current is large, the bias
is …………
1. forward
2. inverse
3. poor
4. reverse
Answer :1
Q17. A crystal diode is a …………… device
1. non-linear
2. bilateral
3. linear
Answer :1
Q18. A crystal diode utilises …………….. characteristic for
rectification
1. reverse
2. forward
3. forward or reverse
Answer :2
Q19. When a crystal diode is used as a rectifier, the most
important consideration is ………..
1. forward characteristic
2. doping level
3. reverse characteristic
4. PIC rating
Answer :4
Q20. If the doping level in a crystal diode is increased, the
width of depletion layer………..
1. remains the same
2. is decreased
3. in increased
Answer :3
Q21. A zener diode has ………..
1. one pn junction
2. two pn junctions
Answer :1
Q22. A zener diode is used as …………….
1. an amplifier
2. a voltage regulator
3. a rectifier
4. a multivibrator
Answer :2
Q23. The doping level in a zener diode is …………… that of a
crystal diode
1. the same as
2. less than
3. more than
Answer :3
Q24. A zener diode is always ………… connected.
1. reverse
2. forward
3. either reverse or forward
Answer :1
Q25. A zener diode utilizes ……….. characteristics for its
operation.
1. forward
2. reverse
3. both forward and reverse
Answer :2
Q26. In the breakdown region, a zener didoe behaves like a
…………… source.
1. constant voltage
2. constant current
3. constant resistance
Answer :1
27. A zener diode is destroyed if it…………..
1. is forward biased
2. is reverse biased
3. carrier more than rated current
Answer :3
Q28. A series resistance is connected in the zener circuit
to………..
1. properly reverse bias the zener
2. protect the zener
3. properly forward bias the zener
Answer :2
A29. A zener diode is …………………. device
1. a non-linear
2. a linear
3. an amplifying
Answer :1
Q30. A zener diode has ………….. breakdown voltage
1. undefined
2. sharp
3. zero
Answer :2
Q31. ……………. rectifier has the lowest forward resistance
1. solid state
2. vacuum tube
3. gas tube
Answer :1
Q32. Mains a.c. power is converrted into d.c. power for
……………..
1. lighting purposes
2. heaters
3. using in electronic equipment
Answer :3
Q33. The disadvantage of a half-wave rectifier is that
the……………….
1. components are expensive
2. diodes must have a higher power rating
3. output is difficult to filter
Answer :3
Q34. If the a.c. input to a half-wave rectifier is an r.m.s value of
400/√2 volts, then diode PIV rating is ………………….
1. 400/√2 V
2. 400 V
3. 400 x √2 V
Answer :2
Q35. The ripple factor of a half-wave rectifier is
…………………
1. 2
2. 1.21
3. 2.5
4. 0.48
Answer :2
Q36. There is a need of transformer for ………………..
1. half-wave rectifier
2. centre-tap full-wave rectifier
3. bridge full-wave rectifier
Answer :2
Q37. The PIV rating of each diode in a bridge rectifier is
……………… that of the equivalent centre-tap rectifier
1. one-half
2. the same as
3. twice
4. four times
Answer :1
Q38. For the same secondary voltage, the output voltage from
a centre-tap rectifier is ………… than that of bridge rectifier
1. twice
2. thrice
3. four time
4. one-half
Answer :4
Q39. If the PIV rating of a diode is exceeded, ………………
1. the diode conducts poorly
2. the diode is destroyed
3. the diode behaves like a zener diode
Answer :2
Q40. A 10 V power supply would use …………………. as filter
capacitor.
1. paper capacitor
2. mica capacitor
3. electrolytic capacitor
4. air capacitor
Answer :3
Q41. A 1,000 V power supply would use ……….. as a filter
capacitor
1. paper capacitor
2. air capacitor
3. mica capacitor
4. electrolytic capacitor
Answer :1
Q42. The ……………….. filter circuit results in the best
voltage regulation
1. choke input
2. capacitor input
3. resistance input
Answer :1
Q43. A half-wave rectifier has an input voltage of 240 V r.m.s.
If the step-down transformer has a turns ratio of 8:1, what is
the peak load voltage? Ignore diode drop.
1. 27.5 V
2. 86.5 V
3. 30 V
4. 42.5 V
Answer :4
Q44. The maximum efficiency of a half-wave rectifier is
………………..
1. 40.6 %
2. 81.2 %
3. 50 %
4. 25 %
Answer :1
Q45. The most widely used rectifier is ……………….
1. half-wave rectifier
2. centre-tap full-wave rectifier
3. bridge full-wave rectifier
Answer :3
Multiple Choice Questions and Answers on Transistors
Q1. A transistor has …………………
1. one pn junction
2. two pn junctions
4. four pn junctions
Answer : 2
Q2. The number of depletion layers in a transistor is …………
1. four
2. three
3. one
4. two
Answer : 4
Q3. The base of a transistor is ………….. doped
1. heavily
2. moderately
3. lightly
Answer : 3
Q4. The element that has the biggest size in a transistor is
………………..
1. collector
2. base
3. emitter
4. collector-base-junction
Answer : 1
Q5. In a pnp transistor, the current carriers are ………….
1. acceptor ions
2. donor ions
3. free electrons
4. holes
Answer : 4
Q6. The collector of a transistor is …………. doped
1. heavily
2. moderately
3. lightly
Answer : 2
Q7. A transistor is a …………… operated device
1. current
2. voltage
3. both voltage and current
Answer : 1
Q8. In a npn transistor, ……………. are the minority carriers
1. free electrons
2. holes
3. donor ions
4. acceptor ions
Answer : 2
Q9. The emitter of a transistor is ………………… doped
1. lightly
2. heavily
3. moderately
Answer : 2
Q10. In a transistor, the base current is about ………….. of
emitter current
1. 25%
2. 20%
3. 35 %
4. 5%
Answer : 4
Q11. At the base-emitter junctions of a transistor, one finds
……………
1. a reverse bias
2. a wide depletion layer
3. low resistance
Answer : 3
Q12. The input impedance of a transistor is ………….
1. high
2. low
3. very high
4. almost zero
Answer : 2
Q13. Most of the majority carriers from the emitter
………………..
1. recombine in the base
2. recombine in the emitter
3. pass through the base region to the collector
Answer :3
Q14. The current IB is …………
1. electron current
2. hole current
3. donor ion current
4. acceptor ion current
Answer : 1
Q15. In a transistor ………………..
IC = IE + IB
IB = IC + IE
IE = IC – IB
IE = IC + IB
Answer : 4
Q16. The value of α of a transistor is ……….
 more than 1
 less than 1
 1
 none of the above
Answer : 2
Q17. IC = αIE + ………….
1. IB
2. ICEO
3. ICBO
4. βIB
Answer : 3
Q18. The output impedance of a transistor is ……………..
1. high
2. zero
3. low
4. very low
Answer : 1
Q19. In a tansistor, IC = 100 mA and IE = 100.2 mA. The value
of β is …………
1. 100
2. 50
3. about 1
4. 200
Answer : 4
Q20. In a transistor if β = 100 and collector current is 10 mA,
then IE is …………
1. 100 mA
2. 100.1 mA
3. 110 mA
Answer : 2
Q21. The relation between β and α is …………..
1. β = 1 / (1 – α )
2. β = (1 – α ) / α
3. β = α / (1 – α )
4. β = α / (1 + α )
Answer : 3
Q22. The value of β for a transistor is generally ………………..
1. 1
2. less than 1
3. between 20 and 500
4. above 500
Answer : 3
Q23. The most commonly used transistor arrangement is
…………… arrangement
1. common emitter
2. common base
3. common collector
Answer : 1
Q24. The input impedance of a transistor connected in
…………….. arrangement is the highest
1. common emitter
2. common collector
3. common base
Answer : 2
Q25. The output impedance of a transistor connected in
……………. arrangement is the highest
1. common emitter
2. common collector
3. common base
Answer : 3
Q26. The phase difference between the input and output
voltages in a common base arrangement is …………….
1. 180o
2. 90o
3. 270o
4. 0o
Answer : 4
Q27. The power gain in a transistor connected in …………….
arrangement is the highest
1. common emitter
2. common base
3. common collector
Answer : 1
voltages of a transistor connected in common emitter
arrangement is ………………
1. 0o
2. 180o
3. 90o
4. 270o
Answer : 2
Q29. The voltage gain in a transistor connected in
………………. arrangement is the highest
1. common base
2. common collector
3. common emitter
Answer : 3
Q30. As the temperature of a transistor goes up, the base-
emitter resistance ……………
1. decreases
2. increases
3. remains the same
Answer : 1
Q31. The voltage gain of a transistor connected in common
collector arrangement is ………..
1. equal to 1
2. more than 10
3. more than 100
4. less than 1
Answer : 4
voltages of a transistor connected in common collector
arrangement is ………………
1. 180o
2. 0o
3. 90o
4. 270o
Answer : 2
Q33. IC = β IB + ………..
1. ICBO
2. IC
3. ICEO
4. αIE
Answer : 3
Q34. IC = [α / (1 – α )] IB + ………….
1. ICEO
2. ICBO
3. IC
4. (1 – α ) IB
Answer : 1
Q35. IC = [α / (1 – α )] IB + […….. / (1 – α )]
1. ICBO
2. ICEO
3. IC
4. IE
Answer : 1
Q36. BC 147 transistor indicates that it is made of …………..
1. germanium
2. silicon
3. carbon
Answer : 2
Q37. ICEO = (………) ICBO
1. β
2. 1 + α
3. 1 + β
Answer : 3
Q38. A transistor is connected in CB mode. If it is not
connected in CE mode with same bias voltages, the values of IE,
IB and IC will …………..
1. remain the same
2. increase
3. decrease
Answer : 1
Q39. If the value of α is 0.9, then value of β is ………..
1. 9
2. 0.9
3. 900
4. 90
Answer : 4
Q40. In a transistor, signal is transferred from a ……………
circuit
1. high resistance to low resistance
2. low resistance to high resistance
3. high resistance to high resistance
4. low resistance to low resistance
Answer : 2
Q41. The arrow in the symbol of a transistor indicates the
direction of ………….
1. electron current in the emitter
2. electron current in the collector
3. hole current in the emitter
4. donor ion current
Answer : 3
Q42. The leakage current in CE arrangement is …………….
that in CB arrangement
1. more than
2. less than
3. the same as
Answer : 1
Q43. A heat sink is generally used with a transistor to
…………
1. increase the forward current
2. decrease the forward current
3. compensate for excessive doping
4. prevent excessive temperature rise
Answer : 4
Q44. The most commonly used semiconductor in the
manufacture of a transistor is ………….
1. germanium
2. silicon
3. carbon
Answer : 2
Q45. The collector-base junction in a transistor has
……………..
1. forward bias at all times
2. reverse bias at all times
3. low resistance
Answer : 2
Multiple Choice Questions and Answers on Transistor Biasing
Q1. Transistor biasing represents ……………. conditions
1. c.
2. c.
3. both a.c. and d.c.
Answer : 2
Q2. Transistor biasing is done to keep ………… in the circuit
1. Proper direct current
2. Proper alternating current
3. The base current small
4. Collector current small
Answer : 1
Q3. Operating point represents …………..
1. Values of IC and VCE when signal is applied
2. The magnitude of signal
3. Zero signal values of IC and VCE
Answer : 3
Q4. If biasing is not done in an amplifier circuit, it results in
……………
1. Decrease in the base current
2. Unfaithful amplification
3. Excessive collector bias
Answer : 2
Q5. Transistor biasing is generally provided by a …………….
1. Biasing circuit
2. Bias battery
3. Diode
Answer : 1
Q6. For faithful amplification by a transistor circuit, the value
of VBE should ………. for a silicon transistor
1. Be zero
2. Be 0.01 V
3. Not fall below 0.7 V
4. Be between 0 V and 0.1 V
Answer : 3
Q7. For proper operation of the transistor, its collector should
have …………
1. Proper forward bias
2. Proper reverse bias
3. Very small size
Answer : 2
Q8. For faithful amplification by a transistor circuit, the value
of VCE should ……….. for silicon transistor
1. Not fall below 1 V
2. Be zero
3. Be 0.2 V
Answer : 1
Q9. The circuit that provides the best stabilization of operating
point is …………
1. Base resistor bias
2. Collector feedback bias
3. Potential divider bias
Answer : 3
Q10. The point of intersection of d.c. and a.c. load lines
represents …………..
1. Operating point
2. Current gain
3. Voltage gain
Answer : 1
Q11. An ideal value of stability factor is …………..
1. 100
2. 200
3. More than 200
4. 1
Answer : 4
Q12. The zero signal IC is generally ……………… mA in the
initial stages of a transistor amplifier
1. 4
2. 1
3. 3
4. More than 10
Answer : 2
Q13. If the maximum collector current due to signal alone is 3
mA, then zero signal collector current should be at least equal
to ………..
1. 6 mA
2. mA
3. 3 mA
4. 1 mA
Answer : 3
Q14. The disadvantage of base resistor method of transistor
biasing is that it …………
1. Is complicated
2. Is sensitive to changes in ß
3. Provides high stability
Answer : 2
Q15. The biasing circuit has a stability factor of 50. If due to
temperature change, ICBO changes by 1 µA, then IC will
change by …………
1. 100 µA
2. 25 µA
3. 20 µA
4. 50 µA
Answer : 4
Q16. For good stabilsation in voltage divider bias, the current
I1 flowing through R1 and R2 should be equal to or greater
than
1. 10 IB
2. 3 IB
3. 2 IB
4. 4 IB
Answer : 1
Q17. The leakage current in a silicon transistor is about
………… the leakage current in a germanium transistor
1. One hundredth
2. One tenth
3. One thousandth
4. One millionth
Answer : 3
Q18. The operating point is also called the ………….
1. Cut off point
2. Quiescent point
3. Saturation point
Answer : 2
Q19. For proper amplification by a transistor circuit, the
operating point should be located at the ………….. of the d.c.
load line
1. The end point
2. Middle
3. The maximum current point
Answer : 2
Q20. The operating point ………………… on the a.c. load line
1. Also line
2. Does not lie
3. May or may not lie
4. Data insufficient
Answer : 1
Q21. The disadvantage of voltage divider bias is that it has
………….
1. High stability factor
2. Low base current
3. Many resistors
Answer : 3
Q22. Thermal runaway occurs when ……….
1. Collector is reverse biased
2. Transistor is not biased
3. Emitter is forward biased
4. Junction capacitance is high
Answer : 2
Q23. The purpose of resistance in the emitter circuit of a
transistor amplifier is to ………….
1. Limit the maximum emitter current
2. Provide base-emitter bias
3. Limit the change in emitter current
Answer : 3
Q24. In a transistor amplifier circuit VCE = VCB + ……………..
1. VBE
2. 2VBE
3. 5 VBE
Answer : 1
Q25. The base resistor method is generally used in ………
1. Amplifier circuits
2. Switching circuits
3. Rectifier circuits
Answer : 2
Q26. For germanium transistor amplifier, VCE should
………….. for faithful amplification
1. Be zero
2. Be 0.2 V
3. Not fall below 0.7 V
Answer : 3
Q27. In a base resistor method, if the value of β changes by 50,
then collector current will change by a factor ………
1. 25
2. 50
3. 100
4. 200
Answer : 2
Q28. The stability factor of a collector feedback bias circuit is
……….. that of base resistor bias.
1. The same as
2. More than
3. Less than
Answer : 3
Q29. In the design of a biasing circuit, the value of collector
load RC is determined by …………
1. VCE consideration
2. VBE consideration
3. IB consideration
Answer : 1
Q30. If the value of collector current IC increases, then the
value of VCE …………
1. Remains the same
2. Decreases
3. Increases
Answer : 2
Q31. If the temperature increases, the value of VCE …………
1. Remains the same
2. Is increased
3. Is decreased
Answer : 3
Q32. The stabilisation of operating point in potential divider
method is provided by ……….
1. RE consideration
2. RC consideration
3. VCC consideration
Answer: 1
Q33. The value of VBE …………….
1. Depends upon IC to moderate extent
2. Is almost independent of IC
3. Is strongly dependant on IC
Answer : 2
Q34. When the temperature changes, the operating point is
shifted due to …….
1. Change in ICBO
2. Change in VCC
3. Change in the values of circuit resistance
Answer : 1
Q35. The value of stability factor for a base resistor bias is
…………
1. RB (β+1)
2. (β+1)RC
3. (β+1)
4. 1-β
Answer : 3
Q36. In a particular biasing circuit, the value of RE is about
………
1. 10 kΩ
2. 1 MΩ
3. 100 kΩ
4. 800 Ω
Answer : 4
Q37. A silicon transistor is biased with base resistor method. If
β=100, VBE =0.7 V, zero signal collector current IC = 1 mA and
VCC = 6V , what is the value of the base resistor RB?
1. 105 kΩ
2. 530 kΩ
3. 315 kΩ
Answer : 2
Q38. In voltage divider bias, VCC = 25 V; R1 = 10 kΩ; R2 = 2.2
V ; RC = 3.6 V and RE =1 kΩ. What is the emitter voltage?
1. 7 V
2. 3 V
 V
3. 8 V
Answer : 4
Q39. In the above question (Q38.) , what is the collector
voltage?
5. 3 V
6. 8 V
7. 6 V
8. 7 V
Answer : 1
Q40. In voltage divider bias, operating point is 3 V, 2 mA. If
VCC = 9 V, RC = 2.2 kΩ, what is the value of RE ?
1. 2000 Ω
2. 1400 Ω
3. 800 Ω
4. 1600 Ω
Answer : 3
Multiple Choice Questions and Answers on Single Stage
Transistor Amplifiers
Q1. A single stage transistor amplifier contains …………….
and associated circuitry
1. Two transistors
2. One transistor
3. Three transistor
Answer : 2
Q2. The phase difference between the output and input
voltages of a CE amplifier is ………………..
1. 180o
2. 0o
3. 90o
4. 270o
Answer : 1
Q3. It is generally desired that a transistor should have
…………….. input impedance
1. Low
2. Very low
3. High
4. Very high
Answer : 3
Q4. When an a.c. signal is applied to an amplifier, ,the
operating point moves along …………….
1. c. load line
2. c. load line
3. both d.c. and a.c. load lines
Answer : 2
Q5. If the collector supply is 10V, then collector cut off voltage
under d.c. conditions is ………….
1. 20 V
2. 5 V
3. 2 V
4. 10 V
Answer : 4
Q6. In the zero signal conditions, a transistor sees
……………….. load
1. c.
2. c.
3. both d.c. and a.c.
Answer : 1
Q7. The input capacitor in an amplifier is the ………………..
capacitor
1. Coupling
2. Bypass
3. Leakage
Answer : 1
Q8. The point of intersection of d.c. and a.c. load lines is called
……………..
1. Saturation point
2. Cut off point
3. Operating point
Answer : 3
Q9. The slope of a.c. load line is ……………… that of d.c. load
line
1. The same as
2. More than
3. Less than
Answer : 2
Q10. If a transistor amplifier draws 2mA when input voltage is
10 V, then its input impedance is ………..
1. 20 kΩ
2. 2 kΩ
3. 10 kΩ
4. 5 kΩ
Answer : 4
Q11. When a transistor amplifier is operating, the current in
any branch is ……………
1. Sum of a.c. and d.c.
2. c. only
3. c. only
4. difference of a.c. and d.c.
Answer : 1
Q12. The purpose of capacitors in a transistor amplifier is to
………………
1. Protect the transistor
2. Cool the transistor
3. Couple or bypass a.c. component
4. Provide biasing
Answer : 3
Q13. In the d.c. equivalent circuit of a transistor amplifier, the
capacitors are considered ……………..
1. Short
2. Open
3. Partially short
Answer : 2
Q14. In a CE amplifier, voltage gain = ……………. x RAC/Rin
1. α
2. (1 + α)
3. (1+ β)
4. β
Answer : 4
Q15. In practice, the voltage gain of an amplifier is expressed
……………..
1. As volts
2. As a number
3. In db
Answer : 3
Q16. If the power and current gains of a transistor amplifier
are 16500 and 100 respectively, then voltage gain is ………
1. 165
2. 165 x 104
3. 100
Answer : 1
Q17. If RC and RL represent the collector resistance and load
resistance respectively in a single stage transistor amplifier,
then a.c. load is ……..
1. RL + RC
2. RC || RL
3. RL – RC
4. RC
Answer : 2
Q18. In a CE amplifier, the phase difference between voltage
across collector load RC and signal voltage is ………..
1. 180o
2. 270o
3. 90o
4. 0o
Answer : 4
Q19. In the a.c. equivalent circuit of a transistor amplifier, the
capacitors are considered ………….
1. Short
2. Open
3. Partially open
Answer : 1
Q20. In a single stage transistor amplifier, RC and RL
represent collector resistance and load resistance respectively.
The transistor sees a d.c. load of ………..
1. RC + RL
2. RC || RL
3. RL
4. RC
Answer : 4
Q21. The purpose of d.c. conditions in a transistor is to
…………..
1. Reverse bias the emitter
2. Forward bias the collector
3. Set up operating point
Answer : 3
Q22. An amplifier has a power gain of 100. Its db gain is
……………
1. 10 db
2. 20 db
3. 40 db
Answer : 2
Q23. In order to get more voltage gain from a transistor
amplifier, the transistor used should have …………..
1. Thin base
2. Thin collector
3. Wide emitter
Answer : 1
Q24. The purpose of a coupling capacitor in a transistor
amplifier is to ……….
1. Increase the output impedance of transistor
2. Protect the transistor
3. Pass a.c. and block d.c.
4. Provide biasing
Answer : 3
Q25. The purpose of emitter capacitor (i.e. capacitor across
RE) is to ……….
1. Avoid voltage gain drop
2. Forward bias the emitter
3. Reduce noise in the amplifier
Answer : 1
Q26. The ratio of output impedance of a CE amplifier is
……………
1. About 1
2. Low
3. High
4. Moderate
Answer : 4
Q27. If a transistor amplifier feeds a load of low resistance (e.g.
speaker), then voltage gain will be ………….
1. High
2. Very high
3. Moderate
4. Low
Answer : 4
Q28. If the input capacitor of a transistor amplifier is short-
circuited, then………
1. Transistor will be destroyed
2. Biasing conditions will change
3. Signal will not reach the base
Answer : 2
Q29. The radio wave picked up by the receiving antenna is
amplified about …….. times to have reasonable sound output
1. 1000
2. A million
3. 100
4. 10000
Answer : 2
Q30. A CE amplifier is also called ………….. circuit
1. Grounded emitter
2. Grounded base
3. Grounded collector
Answer : 1
Q31. The d.c. load of a transistor amplifier is generally
………….. that of a a.c. load
1. The same as
2. Less than
3. More than
Answer : 3
Q32. The value of collector load RC in a transistor amplifier is
………… the output impedance of the transistor.
1. The same as
2. Less than
3. More than
Answer : 2
Q33. A single stage transistor amplifier with collector load
RC and emitter resistance RE has a d.c. load of ……….
1. RC
2. RC || RE
3. RC – RE
4. RC + RE
Answer : 4
Q34. In transistor amplifiers, we generally use …………..
capacitors.
1. Electrolytic
2. Mica
3. Paper
4. Air
Answer : 1
Q35. A single stage transistor amplifier with no load sees an
a.c. load of ……..
1. RC + RE
2. RC
3. RC || RE
4. RC/RE
Answer : 2
Q36. The output power of a transistor amplifier is more than
the input power because the additional power is supplied by
…………
1. Transistor
2. Biasing circuit
3. Collector supply VCC
Answer : 3
Q37. A transistor converts ……………
1. c. power into a.c. power
2. c. power into d.c. power
3. high resistance into low resistance
Answer : 1
Q38. A transistor amplifier has high output impedance
because ………..
1. Emitter is heavily doped
2. Collector has reverse bias
3. Collector is wider than emitter or base
Answer : 2
Q39. For highest power gain, one would use ……………..
configuration
1. CC
2. CB
3. CE
Answer : 3
Q40. CC configuration is used for impedance matching
because its ……………..
1. Input impedance is very high
2. Input impedance is low
3. Output impedance is very low
Answer : 1
Multiple Choice Questions and Answers on Multistage
Transistor Amplifiers
Q1. A radio receiver has …………… of amplification
1. One stage
2. Two stages
3. Three stages
4. More than one stages
Answer : 4
Q2. RC coupling is used for ………………. amplification
1. Voltage
2. Current
3. Power
Answer : 1
Q3. In an RC coupled amplifier, the voltage gain over mid-
frequency range …………….
1. Changes abruptly with frequency
2. Is constant
3. Changes uniformly with frequency
Answer : 2
Q4. In obtaining the frequency response curve of an amplifier,
the …………
1. Amplifier level output is kept constant
2. Amplifier frequency is held constant
3. Generator frequency is held constant
4. Generator output level is held constant
Answer : 4
Q5. An advantage of RC coupling scheme is the ………….
1. Good impedance matching
2. Economy
3. High efficiency
Answer : 2
Q6. The best frequency response is of ………. coupling
1. RC
2. Transformer
3. Direct
Answer : 3
Q7. Transformer coupling is used for ………….. amplification
1. Power
2. Voltage
3. Current
Answer : 1
Q8. In an RC coupling scheme, the coupling capacitor CC must
be large enough ………..
1. To pass d.c. between the stages
2. Not to attenuate the low frequencies
3. To dissipate high power
Answer : 2
Q9. In RC coupling, the value of coupling capacitor is about
……….
1. 100 pF
2. 0.1 µF
3. 0.01 µF
4. 10 µF
Answer : 4
Q10. The noise factor of an ideal amplifier expressed in db is
…………..
1. 0
2. 1
3. 1
4. 10
Answer : 1
Q11. When a multistage amplifier is to amplify d.c. signal, then
one must use …….. coupling
1. RC
2. Transformer
3. Direct
Answer : 3
Q12. ………….. coupling provides the maximum voltage gain
1. RC
2. Transformer
3. Direct
4. Impedance
Answer : 2
Q13. In practice, voltage gain is expressed ……………
1. In db
2. In volts
3. As a number
Answer : 1
Q14. Transformer coupling provides high efficiency because
…………
1. Collector voltage is stepped up
2. c. resistance is low
3. collector voltage is stepped down
Answer : 2
Q15. Transformer coupling is generally employed when load
resistance is ………
1. Large
2. Very large
3. Small
Answer : 3
Q16. If a three-stage amplifier has individual stage gains of 10
db, 5 db and 12 db, then total gain in db is ……….
1. 600 db
2. 24 db
3. 14 db
4. 27 db
Answer : 4
Q17. The final stage of a multistage amplifier uses
………………
1. RC coupling
2. Transformer coupling
3. Direct coupling
4. Impedance coupling
Answer : 2
Q18. The ear is not sensitive to ………….
1. Frequency distortion
2. Amplitude distortion
3. Frequency as well as amplitude distortion
Answer : 1
Q19. RC coupling is not used to amplify extremely low
frequencies because ………
1. There is considerable power loss
2. There is hum in the output
3. Electrical size of coupling capacitor becomes very large
Answer : 3
Q20. In transistor amplifiers, we use ……………. transformer
for impedance matching
1. Step up
2. Step down
3. Same turn ratio
Answer : 2
Q21. The lower and upper cut off frequencies are also called
………………… frequencies
1. Sideband
2. Resonant
3. Half-resonant
4. Half-power
Answer : 4
Q22. A gain of 1,000,000 times in power is expressed by
…………….
1. 30 db
2. 60 db
3. 120 db
4. 600 db
Answer : 2
Q23. A gain of 1000 times in voltage is expressed by …………..
1. 60 db
2. 30 db
3. 120 db
4. 600 db
Answer : 1
Q24. 1 db corresponds to ………….. change in power level
1. 50%
2. 35%
3. 26%
4. 22%
Answer : 3
Q25. 1 db corresponds to …………. change in voltage or
current level
1. 40%
2. 80%
3. 20%
4. 25%
Answer : 1
Q26. The frequency response of transformer coupling is
………….
1. Good
2. Very good
3. Excellent
4. Poor
Answer : 4
Q27. In the initial stages of a multistage amplifier, we use
………..
1. RC coupling
2. Transformer coupling
3. Direct coupling
Answer : 1
Q28. The total gain of a multistage amplifier is less than the
product of the gains of individual stages due to …………
1. Power loss in the coupling device
2. Loading effect of the next stage
3. The use of many transistors
4. The use of many capacitors
Answer : 2
Q29. The gain of an amplifier is expressed in db because
………..
1. It is a simple unit
2. Calculations become easy
3. Human ear response is logarithmic
Answer : 3
Q30. If the power level of an amplifier reduces to half, the db
gain will fall by …….
1. 5 db
2. 2 db
3. 10 db
4. 3 db
Answer : 4
Q31. A current amplification of 2000 is a gain of …………….
1. 3 db
2. 66 db
3. 20 db
4. 200 db
Answer : 2
Q32. An amplifier receives 0.1 W of input signal and delivers
15 W of signal power. What is the power gain in db?
1. 8 db
2. 6 db
3. 5 db
4. 4 db
Answer : 1
Q33. The power output of an audio system is 18 W. For a
person to notice an increase in the output (loudness or sound
intensity) of the system, what must the output power be
increased to ?
1. 2 W
2. 6 W
3. 68 W
Answer : 3
Q34. The output of a microphone is rated at -52 db. The
reference level is 1V under specified conditions. What is the
output voltage of this microphone under the same sound
conditions?
1. 5 mV
2. 2 mV
3. 8 mV
4. 5 mV
Answer : 4
Q35. RC coupling is generally confined to low power
applications because of ………
1. Large value of coupling capacitor
2. Low efficiency
3. Large number of components
Answer : 2
Q36. The number of stages that can be directly coupled is
limited because ……..
1. Changes in temperature cause thermal instability
2. Circuit becomes heavy and costly
3. It becomes difficult to bias the circuit
Answer : 1
Q37. The purpose of RC or transformer coupling is to
…………
1. Block a.c.
2. Separate bias of one stage from another
3. Increase thermal stability
Answer : 2
Q38. The upper or lower cut off frequency is also called
………….. frequency
1. Resonant
2. Sideband
3. 3 db
Answer : 3
Q39. The bandwidth of a single stage amplifier is ………….
that of a multistage amplifier
1. More than
2. The same as
3. Less than
Answer : 1
Q40. The value of emitter capacitor CE in a multistage
amplifier is about ……..
1. 1 µF
2. 100 pF
3. 0.01 µF
4. 50 µF
Answer : 4
Multiple Choice Questions and Answers on Transistor Audio
Power Amplifiers
Q1. The output stage of a multistage amplifier is also called
……………
1. Mixer stage
2. Power stage
3. Detector stage
4. F stage
Answer : 2
Q2. ………………. coupling is generally employed in power
amplifiers
1. Transformer
2. RC
3. direct
4. Impedance
Answer : 1
Q3. A class A power amplifier uses …………
1. Two transistors
2. Three transistors
3. One transistor
Answer : 3
Q4. The maximum efficiency of resistance loaded class A
power amplifier is ……..
1. 5%
2. 50%
3. 30%
4. 25%
Answer : 4
Q5. The maximum efficiency of transformer coupled class A
power amplifier is ………………
1. 30%
2. 50%
3. 80%
4. 45%
Answer : 2
Q6. Class……. power amplifier has the highest collector
efficiency
1. C
2. A
3. B
4. AB
Answer : 1
Q7. Power amplifiers handle …………. signals compare to
voltage amplifiers
1. Small
2. Very small
3. Large
Answer : 3
Q8. In class A operation, the operating point is generally
located ………. of the d.c. load line.
1. At cut off point
2. At the middle
3. At saturation point
Answer : 2
Q9. Class C amplifiers are used as …………….
1. AF amplifiers
2. Detectors
3. F. amplifiers
Answer : 3
Q10. A power amplifier has comparatively …………….. β
1. Small
2. Large
3. Very large
Answer : 1
Q11. The maximum collector efficiency of class B operation is
……………..
1. 50%
2. 90%
3. 5%
4. 5%
Answer : 4
Q12. A 2-transistor class B power amplifier is commonly called
……….. amplifier
1. Dual
2. Push-pull
3. Symmetrical
4. Differential
Answer : 2
Q13. If a transistor is operated in such a way that output
current flows for 60o of the input signal, then it is ……………
operation
1. Class A
2. Class B
3. Class C
Answer : 3
Q14. If the zero signal dissipation of a transistor is 1W, then
power rating of the transistor should be at least ……………….
1. 5 W
2. 33 W
3. 75 W
4. 1 W
Answer : 4
Q15. When a transistor is cut off……………..
1. Maximum voltage appears across transistor
2. Maximum current flows
3. Maximum voltage appears across load
Answer : 1
Q16. A class A power amplifier is sometimes called …………..
amplifier
1. Symmetrical
2. Single-ended
3. Reciprocating
4. Differential
Answer : 2
Q17. Class ………….. operation gives the maximum distortion
1. A
2. B
3. C
4. AB
Answer : 3
Q18. The output stage of a multistage amplifier usually
employs ………..
1. Push-pull amplifier
2. Preamplifier
3. Class A power amplifier
Answer : 1
Q19. The size of a power transistor is made considerably large
to …………
1. Provide easy handling
2. Dissipate heat
3. Facilitate connections
Answer : 2
Q20. Low efficiency of a power amplifier results in
……………….
1. Low forward bias
2. Less battery consumption
3. More battery consumption
Answer : 3
Q21. The driver stage usually employs………….
1. Class A power amplifier
2. Push-pull amplifier
3. Class C amplifier
Answer : 1
Q22. If the power rating of a transistor is 1W and collector
current is 100mA, then maximum allowable collector voltage is
………..
1. 1V
2. 100V
3. 20V
4. 10V
Answer : 4
Q23. When no signal is applied, the approximate collector
efficiency of class A power amplifier is …….
1. 10%
2. 0%
3. 25%
4. 50%
Answer : 2
Q24. What will be the collector efficiency of a power amplifier
having zero signal power dissipation of 5 watts and a.c. power
output of 2 watts?
1. 20%
2. 80%
3. 40%
4. 50%
Answer : 3
Q25. The output signal voltage and current of a power
amplifier are 5V and 200 mA; the values being r.m.s. What is
the power output?
1. 1 W
2. 2 W
3. 4 W
Answer : 1
Q26. The maximum a.c. power output from a class A power
amplifier is 10 W. What should be the minimum power rating
of the transistor used ?
1. 10 W
2. 15 W
3. 5 W
4. 20 W
Answer : 4
Q27. For the same a.c. power output as above, what should be
the minimum power rating of transistor for class B operation?
1. 10 W
2. 4 W
3. 8 W
Answer : 2
Q28. The push-pull circuit must use …………… operation
1. Class A
2. Class C
3. Class B
4. Class AB
Answer : 3
Q29. The class B push-pull circuit can deliver 100 W of a.c.
output power. What should be the minimum power rating of
each transistor?
1. 20 W
2. 40 W
3. 10 W
4. 80 W
Answer : 1
Q30. What turn ratio (Np/Ns) of transformer is required to
match 4 Ω speaker to a transistor having an output impedance
of 8000 Ω?
1. 2
2. 7
3. 3
Answer : 2
Q31. A transformer coupled class A power amplifier has a load
of 100 Ω on the secondary. If the turn ratio is 10:1, what is the
value of load appearing on the primary?
1. 5 kΩ
2. 20 kΩ
3. 100 kΩ
4. 10 kΩ
Answer : 4
Q32. Power amplifiers generally use transformer coupling
because transformer permits……..
1. Cooling of the circuit
2. Impedance matching
3. Distortionless output
4. Good frequency response
Answer : 2
Q33. Transformer coupling can be used in ……………
amplifiers
1. Either power or voltage
2. Only power
3. Only voltage
Answer : 1
Q34. The output transformer used in a power amplifier is a
……………. transformer
1. 1:1 ratio
2. Step-up
3. Step-down
Answer : 3
Q35. The most important consideration in power amplifier is
………..
1. Biasing the circuit
2. Collector efficiency
3. To keep the transformer cool
Answer : 2
Q36. An AF amplifier is shielded to …………
1. Keep the amplifier cool
2. Protect from rusting
3. Prevent induction due to stray magnetic fields
Answer : 3
Q37. The pulsating d.c. applied to power amplifier causes
……………..
1. Burning of transistor
2. Hum in the circuit
3. Excessive forward voltage
Answer : 2
Q38. The disadvantage of impedance matching is that it
………………….
1. Gives distorted output
2. Gives low power output
3. Requires a transformer
Answer : 1
Q39. If the gain versus frequency curve of a transistor
amplifier is not flat, then there is distortion.
1. Amplitude
2. Intermodulation
3. Frequency
Answer : 3
Q40. The most costly coupling is ……………… coupling
1. RC
2. Direct
3. Impedance
4. Transformer
Answer : 4
Multiple Choice Questions and Answers on Amplifiers with
Negative Feedback
Q1. When negative voltage feedback is applied to an amplifier,
its voltage gain ……………….
1. Is increased
2. Is reduced
3. Remains the same
Answer : 2
Q2. The value of negative feedback fraction is always
…………….
1. Less than 1
2. More than 1
3. Equal to 1
Answer : 1
Q3. If the output of an amplifier is 10 V and 100 mV from the
output is fed back to the input, then feedback fraction is
………..
1. 10
2. 1
3. 01
4. 15
Answer : 3
Q4. The gain of an amplifier without feedback is 100 db. If a
negative feedback of 3 db is applied, the gain of the amplifier
will become …………..
1. 5 db
2. 300 db
3. 103 db
4. 97 db
Answer : 4
Q5. If the feedback fraction of an amplifier is 0.01, then voltage
gain with negative feedback is approximately………..
1. 500
2. 100
3. 1000
4. 5000
Answer : 2
Q6. A feedback circuit usually employs ……………… network
1. Resistive
2. Capacitive
3. Inductive
Answer : 1
Q7. The gain of an amplifier with feedback is known as
………….. gain
1. Resonant
2. Open loop
3. Closed loop
Answer : 3
Q8. When voltage feedback (negative) is applied to an
amplifier, its input impedance ………….
1. Is decreased
2. Is increased
3. Remains the same
Answer : 2
Q9. When current feedback (negative) is applied to an
amplifier, its input impedance …………..
1. Is decreased
2. Is increased
3. Remains the same
Answer : 1
Q10. Negative feedback is employed in ……………..
1. Oscillators
2. Rectifiers
3. Amplifiers
Answer : 3
Q11. Emitter follower is used for …………
1. Current gain
2. Impedance matching
3. Voltage gain
Answer : 2
Q12. The voltage gain of an emitter follower is ………..
1. Much less than 1
2. Approximately equal to 1
3. Greater than 1
Answer : 2
Q13. When current feedback (negative) is applied to an
amplifier, its output impedance ……..
1. Is increased
2. Is decreased
3. Remains the same
Answer : 1
Q14. Emitter follower is a ……………….. circuit
1. Voltage feedback
2. Current feedback
3. Both voltage and current feedback
Answer : 2
Q15. If voltage feedback (negative) is applied to an amplifier,
its output impedance …………..
1. Remains the same
2. Is increased
3. Is decreased
Answer : 3
Q16. When a negative voltage feedback is applied to an
amplifier, its bandwidth……….
1. Is increased
2. Is decreased
3. Remains the same
4. Insufficient data
Answer : 1
Q17. An emitter follower has ………… input impedance
1. Zero
2. Low
3. High
Answer : 3
Q18. This question will be available soon
Q19. The output impedance of an emitter follower is ……….

1. High
2. Very high
3. Almost zero
4. Low
Answer : 4
Multiple Choice Questions and Answers on Oscillators
Q1. An oscillator converts ……………..
1. c. power into d.c. power
2. c. power into a.c. power
3. mechanical power into a.c. power
Answer : 2
Q2. In an LC transistor oscillator, the active device is
……………
1. LC tank circuit
2. Biasing circuit
3. Transistor
Answer : 3
Q3. In an LC circuit, when the capacitor is maximum, the
inductor energy is ……….
1. Minimum
2. Maximum
3. Half-way between maximum and minimum
Answer : 1
Q4. In an LC oscillator, the frequency of oscillator is
……………. L or C.
1. Proportional to square of
2. Directly proportional to
3. Independent of the values of
4. Inversely proportional to square root of
Answer : 4
Q5. An oscillator produces……………. oscillations
1. Damped
2. Undamped
3. Modulated
Answer : 2
Q6. An oscillator employs ……………… feedback
1. Positive
2. Negative
3. Neither positive nor negative
Answer : 1
Q7. An LC oscillator cannot be used to produce
……………….. frequencies
1. High
2. Audio
3. Very low
4. Very high
Answer : 3
Q8. Hartley oscillator is commonly used in ………………
1. Radio receivers
2. Radio transmitters
3. TV receivers
Answer : 1
Q9. In a phase shift oscillator, we use …………. RC sections
1. Two
2. Three
3. Four
Answer : 2
Q10. In a phase shift oscillator, the frequency determining
elements are …………
1. L and C
2. R, L and C
3. R and C
Answer : 3
Q11. A Wien bridge oscillator uses ……………. feedback
1. Only positive
2. Only negative
3. Both positive and negative
Answer : 3
Q12. The piezoelectric effect in a crystal is ……………
1. A voltage developed because of mechanical stress
2. A change in resistance because of temperature
3. A change in frequency because of temperature
Answer : 1
Q13. If the crystal frequency changes with temperature, we say
that crystal has ………….. temperature coefficient
1. Positive
2. Zero
3. Negative
Answer : 1
Q14. The crystal oscillator frequency is very stable due to
………………. of the crystal
1. Rigidity
2. Vibrations
3. Low Q
4. High Q
Answer : 4
Q15. The application where one would most likely find a
crystal oscillator is ……………..
1. Radio receiver
2. Radio transmitter
3. AF sweep generator
Answer : 2
Q16. An oscillator differs from an amplifier because it ………
1. Has more gain
2. Requires no input signal
3. Requires no d.c. supply
4. Always has the same input
Answer : 2
Q17. One condition for oscillation is ………….
1. A phase shift around the feedback loop of 180o
2. A gain around the feedback loop of one-third
3. A phase shift around the feedback loop of 0o
4. A gain around the feedback loop of less than 1
Answer : 3
Q18. A second condition for oscillations is ……………….
1. A gain of 1 around the feedback loop
2. No gain around the feedback loop
3. The attention of the feedback circuit must be one-third
4. The feedback circuit must be capacitive
Answer : 1
Q19. In a certain oscillator Av = 50. The attention of the
feedback circuit must be …………
1. 1
2. 01
3. 10
4. 02
Answer : 4
Q20. For an oscillator to properly start, the gain around the
feedback loop must initially be
1. 1
2. Greater than 1
3. Less than 1
4. Equal to attenuation of feedback circuit
Answer : 2
Q21. In a Wien-bridge oscillator, if the resistances in the
positive feedback circuit are decreased, the frequency……….
1. Remains the same
2. Decreases
3. Increases
Answer : 3
Q22. In Colpitt’s oscillator, feedback is obtained …………….
1. By magnetic induction
2. By a tickler coil
3. From the centre of split capacitors
Answer : 3
Q23. The Q of the crystal is of the order of …………
1. 100
2. 1000
3. 50
4. More than 10,000
Answer : 4
Q24. Quartz crystal is most commonly used in crystal
oscillators because ………….
1. It has superior electrical properties
2. It is easily available
3. It is quite inexpensive
Answer : 1
Q27. ………….. is a fixed frequency oscillator

1. Phase-shift oscillator
2. Hartely-oscillator
3. Colpitt’s oscillator
4. Crystal oscillator
Answer : 4
Q28. In an LC oscillator, if the value of L is increased four
times, the frequency of oscillations is …………
1. Increased 2 times
2. Decreased 4 times
3. Increased 4 times
4. Decreased 2 times
Answer : 4
Q29. An important limitation of a crystal oscillator is
……………
1. Its low output
2. Its high Q
3. Less availability of quartz crystal
4. Its high output
Answer : 1
Q30. The signal generator generally used in the laboratories is
………….. oscillator
1. Wien-bridge
2. Hartely
3. Crystal
4. Phase shift
Answer : 1
Multiple Choice Questions and Answers on Transistor Tuned
Amplifiers
Q1. A tuned amplifier uses ……………. load
1. Resistive
2. Capacitive
3. LC tank
4. Inductive
Answer : 3
Q2. A tuned amplifier is generally operated in …………….
operation
1. Class A
2. Class C
3. Class B
Answer : 2
Q3. A tuned amplifier is used in …………… applications
1. Radio frequency
2. Low frequency
3. Audio frequency
Answer : 1
Q4. Frequencies above …………… kHz are called radio
frequencies
1. 2
2. 10
3. 50
4. 200
Answer : 4
Q5. At series or parallel resonance, the circuit power factor is
…………..
1. 0
2. 5
3. 1
4. 8
Answer : 3
Q6. The voltage gain of a tuned amplifier is ……………. at
resonant frequency
1. Minimum
2. Maximum
3. Half-way between maximum and minimum
4. Zero
Answer : 2
Q7. At parallel resonance, the line current is ……………….
1. Minimum
2. Maximum
3. Quite large
Answer : 1
Q8. At series resonance, the circuit offers ……………..
impedance
1. Zero
2. Maximum
3. Minimum
Answer : 3
Q9. A resonant circuit contains ……………… elements
1. R and L only
2. R and C only
3. Only R
4. L and C
Answer : 4
Q10. At series or parallel resonance, the circuit behaves as a
…………….. load
1. Capacitive
2. Resistive
3. Inductive
Answer : 2
Q11. At series resonance, voltage across L is ……………….
voltage across C
1. Equal to but opposite in phase to
2. Equal to but in phase with
3. Greater than but in phase with
4. Less than but in phase with
Answer : 1
Q12. When either L or C is increased, the resonant frequency
of LC circuit ……………
1. Remains the same
2. Increases
3. Decreases
Answer : 3
Q13. At parallel resonance, the net reactive component circuit
current is …………
1. Capacitive
2. Zero
3. Inductive
Answer : 2
Q14. In parallel resonance, the circuit impedance is …………..
1. C/LR
2. R/LC
3. CR/L
4. L/CR
Answer : 4
Q15. In a parallel LC circuit, if the input signal frequency is
increased above resonant frequency then …………………..
1. XL increases and XC decreases
2. XL decreases and XC increases
3. Both XL and XC increase
4. Both XL and XC decrease
Answer : 1
Q16. The Q of an LC circuit is given by ………………….
1. 2πfr x R
2. R / 2πfrL
3. 2πfrL / R
4. R2/2πfrL
Answer : 3
Q17. If Q of an LC circuit increases, then bandwidth
…………………
1. Increases
2. Decreases
3. Remains the same
Answer : 2
Q18. At series resonance, the net reactive component of circuit
current is ……………….
1. Zero
2. Inductive
3. Capacitive
Answer : 1
Q19. The dimensions of L/CR are that of …………….
1. Farad
2. Henry
3. Ohm
Answer : 3
Q20. If L/C ratio of a parallel LC circuit is increased, the Q of
the circuit ……………..
1. Is decreased
2. Is increased
3. Remains the same
Answer : 2
Q21. At series resonance, the phase angle between applied
voltage and circuit is ………..
1. 90o
2. 180o
3. 0o
Answer : 3
Q22. At parallel resonance, the ratio L/C is …………….
1. Very large
2. Zero
3. Small
Answer : 1
Q23. If the resistance of a tuned circuit is increased, the Q of
the circuit ………….
1. Is increased
2. Is decreased
3. Remains the same
Answer : 2
Q24. The Q of a tuned circuit refers to the property of
…………..
1. Sensitivity
2. Fidelity
3. Selectivity
Answer : 3
Q25. At parallel resonance, the phase angle between the
applied voltage and circuit current is …………….
1. 90o
2. 180o
3. 0o
Answer : 3
Q26. In a parallel LC circuit, if the signal frequency is
decreased below the resonant frequency, then ……………
1. XL decreases and XC increases
2. XL increases and XC decreases
3. Line current becomes minimum
Answer : 1
Q27. In series resonance, there is ………………
1. Voltage amplification
2. Current amplification
3. Both voltage and current amplification
Answer : 1
Q28. The Q of a tuned amplifier is generally …………….
1. Less than 5
2. Less than 10
3. More than 10
Answer : 3
Q29. The Q of a tuned amplifier is 50. If the resonant
frequency for the amplifier is 1000kHZ, then bandwidth is
…………
1. 10kHz
2. 40 kHz
3. 30 kHz
4. 20 kHz
Answer : 4
Q30. In the above question, what are the values of cut-off
frequencies?
1. 140 kHz , 60 kHz
2. 1020 kHz , 980 kHz
3. 1030 kHz , 970 kHz
Answer : 2
Q31. For frequencies above the resonant frequency, a parallel
LC circuit behaves as a ……………. load
1. Capacitive
2. Resistive
3. Inductive
Answer : 1
Q32. In parallel resonance, there is …………
1. Both voltage and current amplification
2. Voltage amplifications
3. Current amplification
Answer : 3
Q33. For frequencies below resonant frequency, a series LC
circuit behaves as a ………… load
1. Resistive
2. Capacitive
3. Inductive
Answer : 2
Q34. If a high degree of selectivity is desired, then double-
tuned circuit should have …………. coupling
1. Loose
2. Tight
3. Critical
Answer : 1
Q35. In the double tuned circuit, if the mutual inductance
between the two tuned circuits is decreased, the level of
resonance curve ………..
1. Remains the same
2. Is lowered
3. Is raised
Answer : 3
Q36. For frequencies above the resonant frequency , a series
LC circuit behaves as a ………….. load
1. Resistive
2. Inductive
3. Capacitive
Answer : 2
Q37. Double tuned circuits are used in ……………. stages of a
radio receiver
1. IF
2. Audio
3. Output
Answer : 1
Q38. A class C amplifier always drives ………. load
1. A pure resistive
2. A pure inductive
3. A pure capacitive
4. A resonant tank
Answer : 4
Q39. Tuned class C amplifiers are used for RF signals of
………………
1. Low power
2. High power
3. Very high power
Answer : 4
Q40. For frequencies below the resonant frequency , a parallel
LC circuit behaves as a …………… load
1. Inductive
2. Resistive
3. Capacitive
Answer : 1
Multiple Choice Questions and Answers on Modulation and
Demodulation
Q1. Modulation is done in …………..
1. Transmitter
2. Radio receiver
3. Between transmitter and radio receiver
Answer : 1
Q2. In a transmitter ……………. oscillator is used
1. Hartley
2. RC phase-shift
3. Wien-bridge
4. Crystal
Answer : 4
Q3. In India, ……………. modulation is used for radio
transmission
1. Frequency
2. Amplitude
3. Phase
Answer : 2
Q4. In an AM wave useful power is carrier by ………….
1. Carrier
2. Sidebands
3. Both sidebands and carrier
Answer : 2
Q5. In amplitude modulation, bandwidth is ……………. the
audio signal frequency
1. Thrice
2. Four times
3. Twice
Answer : 3
Q6. In amplitude modulation, the ………… of carrier is varied
according to the strength of the signal.
1. Amplitude
2. Frequency
3. Phase
Answer : 1
Q7. Overmodulation (amplitude) occurs when signal amplitude
is …………. carrier amplitude
1. Equal to
2. Greater than
3. Less than
Answer : 2
Q8. In an AM wave, the majority of the power is in
…………….
1. Lower sideband
2. Upper sideband
3. Carrier
Answer : 3
Q9. At 100% modulation, the power in each sideband is
………………… of that of carrier
1. 50%
2. 40%
3. 60%
4. 25%
Answer : 4
Q10. Overmodulation results in …………..
1. Weakening of the signal
2. Excessive carrier power
3. Distortion
Answer : 3
Q11. If modulation is 100% then signal amplitude is …………..
carrier amplitude
1. Equal to
2. Greater than
3. Less than
Answer : 1
Q12. As the modulation level is increased, the carrier power
…………..
1. Is increased
2. Remains the same
3. Is decreased
Answer : 2
Q13. Demodulation is done in …………
1. Receiving antenna
2. Transmitter
3. Radio receiver
4. Transmitting antenna
Answer : 3
Q14. A high Q tuned circuit will permit an amplifier to have
high ……………
1. Fidelity
2. Frequency range
3. Sensitivity
4. Selectivity
Answer : 4
Q15. In radio transmission, the medium of transmission is
……………..
1. Space
2. An antenna
3. Cable
Answer : 1
Q16. If level of modulation is increased ……………. power is
increased
1. Carrier
2. Sideband
3. Carrier as well as sideband
Answer : 2
Q17. In TV transmission, picture signal is ………………
modulated
1. Frequency
2. Phase
3. Amplitude
Answer : 3
Q18. In a radio receiver, noise is generally developed at
………….
1. IF stage
3. Audio stage
4. RF stage
Answer : 4
Q19. Man made noise are …………. variations.
1. Amplitude
2. Frequency
3. Phase
4. Both phase and frequency
Answer : 1
Q20. The signal voltage induced in the aerial of a radio
receiver is of the order of …………….
1. mV
2. µV
3. V
Answer : 2
Q21. Superhertodyne principle refers to
1. Using a large number of amplifier stages
2. Using a push-pull circuit
3. Obtaining lower fixed intermediate frequency
Answer : 3
Q22. If a radio receiver amplifies all the signal frequencies
equally well, it is said to have high …………
1. Sensitivity
2. Selectivity
3. Distortion
4. Fidelity
Answer : 4
Q23. Most of the amplification in a superhetrodyne receiver
occurs at ………. stage
1. IF
2. RF amplifier
3. Audio amplifier
4. Detector
Answer : 1
Q24. The letters AVC stand for …………..
1. Audio voltage control
2. Abrupt voltage control
3. Automatic volume control
4. Automatic voltage control
Answer : 3
Q25. The superhetrodyne principle provides selectivity at
………. stage
1. RF
2. IF
3. audio
4. Before RF
Answer : 2
Q26. In superhetrodyne receiver, the input at mixer stage is
……….
1. IF and RF
2. RF and AF
3. IF and AF
4. RF and local oscillator signal
Answer : 4
Q27. The major advantage of FM over AM is …………..
1. Reception is less noisy
2. Higher carrier frequency
3. Smaller bandwidth
4. Small frequency deviation
Answer : 1
Q28. When the modulating signal controls the frequency of the
carrier, we get……….
1. Phase modulation
2. Amplitude modulation
3. Frequency modulation
4. May be any one of the above
Answer : 3
Q29. Modulation refers to a low-frequency signal controlling
the …………
1. Amplitude of the carrier
2. Frequency of the carrier
3. Phase of the carrier
4. May be any of the above
Answer : 4
Q30. The IF is 455 kHz. If the radio receiver is tuned to 855
kHz, the local oscillator frequency is ………….
1. 455 kHz
2. 1310 kHz
3. 1500 kHz
4. 1520 kHz
Answer : 2
Q31. If Amin = 40 and Amax = 60, what is the percentage of
modulation?
1. 20 %
2. 40 %
3. 50 %
4. 10 %
Answer : 1
Q32. The function of ferrite antenna is to …………….
1. Reduce stray capacitance
2. Stabilise d.c. bias
3. Increase the Q of tuned circuit
4. Reduce noise
Answer : 3
Q33. In a radio receiver, we generally use ………….. oscillator
as a local oscillator
1. Crystal
2. Wien-bridge
3. Phase-shift
4. Hartley
Answer : 4
Q34. A 100 V carrier is made to vary between 160 V and 40 V
by the signal. What is the modulation factor?
1. 3
2. 6
3. 5
Answer : 2
Q35. A 50 kW carrier is to be amplitude modulated to a level
of 85%. What is the carrier power after modulation?
1. 50 kW
2. 5 kW
3. 8 kW
4. 25 kW
Answer : 1
Q36. In the above question, what is the power in sidebands?
1. 8 kW
2. 6 kW
3. 06 kW
4. 9 kW
Answer : 3
Q37. In a superhetrodyne receiver, the difference frequency is
chosen as the IF rather than the sum frequency because
…………….
1. The difference frequency is closer to oscillator frequency
2. Lower frequencies are easier to amplify
3. Only the difference frequency can be modulated
Answer : 2
Q38. The diode detector in an AM radio receiver is usually
found ………….
1. Before the first RF stage
2. After the first RF stage
3. After several stages of amplification
Answer : 3
Q39. In a TRF radio receiver, the RF and detection stages are
tuned to …………
1. Radio frequency
2. IF
3. Audio frequency
Answer : 1
Q40. In TV transmission, sound signal is …………………
modulated
1. Amplitude
2. Frequency
3. Phase
Answer : 2
Multiple Choice Questions and Answers on Regulated DC
Power Supply
Q1. In an unregulated power supply, if load current increases,
the output voltage ………..
1. Remains the same
2. Decreases
3. Increases
Answer : 2
Q2. In an unregulated power supply, if input a.c. voltage
increases, the output voltage …….
1. Increases
2. Decreases
3. Remains the same
Answer : 1
Q3. A power supply which has voltage regulation of ……….. is
unregulated power supply
1. 0 %
2. 5 %
3. 10 %
4. 8%
Answer : 3
Q4. Commercial power supplies have voltage regulation
………….
1. of 10%
2. of 15%
3. of 25%
4. within 1%
Answer : 4
Q5. An ideal regulated power supply is one which has voltage
regulation of …………
1. 0%
2. 5%
3. 10%
4. 1%
Answer : 1
Q6. A Zener diode utilises ………… characteristic for voltage
regulation
1. Forward
2. Reverse
3. Both forward and reverse
Answer : 2
Q7. Zener diode can be used as …………
1. c. voltage regulator only
2. c. voltage regulator only
3. both d.c. and a.c. voltage regulator
Answer : 3
Q8. A Zener diode is used as a …………… voltage regulating
device
1. Shunt
2. Series
3. Series-shunt
Answer : 1
Q9. As the junction temperature increases, the voltage
breakdown point for Zener mechanism …………
1. Is increased
2. Is decreased
3. Remains the same
Answer : 2
Q10. The rupture of co-valent bonds will occur when the
electric field is ………….
1. 100 V/cm
2. 6 V/cm
3. 1000 V/cm
4. More than 105 V/cm
Answer : 4
Q11. In a 15 V Zener diode , the breakdown mechanism will
occur by ………….
1. Avalanche mechanism
2. Zener mechanism
3. Both Zener and avalanche mechanism
Answer : 1
Q12. A Zener diode that has very narrow depletion layer will
breakdown by ……… mechanism
1. Avalanche
2. Zener
3. Both avalanche and Zener
Answer : 2
Q13. As the junction temperature increases, the voltage
breakdown point for avalanche mechanism ………….
1. Remains the same
2. Decrease
3. Increases
Answer : 3
Q14. Another name for Zener diode is ………… diode
1. Breakdown
2. Voltage
3. Power
4. Current
Answer : 1
Q15. Zener diode are generally made of ……….
1. Germanium
2. Silicon
3. Carbon
Answer : 2
Q16. For increasing the voltage rating, zeners are connected in
…………..
1. Parallel
2. Series-parallel
3. Series
Answer : 3
Q17. In a Zener voltage regulator, the changes in load current
produce changes in …………….
1. Zener current
2. Zener voltage
3. Zener voltage as well as Zener current
Answer : 1
Q18. A Zener voltage regulator is used for …………… load
currents
1. High
2. Very high
3. Moderate
4. Small
Answer : 4
Q19. A Zener voltage regulator will cease to act as a voltage
regulator if Zener current becomes ……………
1. Less than load current
2. Zero
3. More than load current
Answer : 2
Q20. If the doping level is increased, the breakdown voltage of
the Zener …………..
1. Remains the same
2. Is increased
3. Is decreased
Answer : 3
Q21. A 30 V Zener will have depletion layer width ………….
that of 10 V Zener
1. More than
2. Less than
3. Equal to
Answer : 1
Q22. The current in a Zener diode is limited by …………..
1. External resistance
2. Power dissipation
3. Both (1) and (2)
Answer : 3
Q23. A 5 mA changes in Zener current produces a 50 mA
change in Zener voltage. What is the Zener impedance?
1. 1 Ω
2. 1 Ω
3. 100 Ω
4. 10 Ω
Answer : 4
Q24. A certain regulator has a no-load voltage of 6 V and a
full-load output of 5.82 V. What is the load regulation?
1. 09%
2. 87 %
3. 72 %
Answer : 1
Q25. What is true about the breakdown voltage in a Zener
diode?
1. It decreases when load current increases
2. It destroys the diode
3. It equals current times the resistance
4. It is approximately constant
Answer : 4
Q26. Which of these is the best description for a Zener diode?
1. It is a diode
2. It is a constant current device
3. It is a constant-voltage device
4. It works in the forward region
Answer : 3
Q27. A Zener diode …………..
1. Is a battery
2. Acts like a battery in the breakdown region
3. Has a barrier potential of 1 V
4. Is forward biased
Answer : 2
Q28. The load voltage is approximately constant when a Zener
diode is ……….
1. Forward biased
2. Unbiased
3. Reverse biased
4. Operating in the breakdown region
Answer : 4
Q29. In a loaded Zener regulator, which is the largest Zener
current?
1. Series current
2. Zener current
3. Load current
Answer : 1
Q30. If the load resistance decreases in a Zener regulator, then
Zener current …………….
1. Decreases
2. Stays the same
3. Increases
Answer : 1
Q31. If the input a.c. voltage to regulated or ordinary power
supply increases by 5% what will be the approximate change
in d.c. output voltage?
1. 10%
2. 20%
3. 15%
4. 5%
Answer : 4
Q32. If the load current drawn by unregulated power supply
increases, the d.c. output voltage ………..
1. Increases
2. Decreases
3. Stays the same
Answer : 2
Q33. If the load current drawn by unregulated power supply
increases, the d.c. output voltage ………
1. Increases
2. Decreases
3. Stays the same
Answer : 2
Q34. A power supply has a voltage regulation of 1%. If the no-
load voltage is 20 V, what is the full-load voltage?
1. 8 V
2. 7 V
3. 6 V
4. 2 V
Answer : 1
Q35. Two similar 15 V Zeners are connected in series. What is
the regulated output voltage?
1. 15 V
2. 5 V
3. 30 V
4. 45 V
Answer : 3
Q36. A power supply can deliver a maximum rated current of
0.5 A at full-load output voltage of 20 V. What is the minimum
load resistance that you can connect across the supply?
1. 10 Ω
2. 20 Ω
3. 15 Ω
4. 40 Ω
Answer : 4
Q37. In a regulated power supply, two similar 15 V zeners are
connected in series. The input voltage is 45 V d.c. If each Zener
has a maximum current rating of 300 mA, what should be the
value of the series resistance?
1. 10 Ω
2. 50 Ω
3. 25 Ω
4. 40 Ω
Answer : 2
Q38. A Zener regulator …………… in the power supply
1. Increases the ripple
2. Decreases the ripple
3. Neither increases nor decreases the ripple
Answer : 2
Q39. When load current is zero, the Zener current will be
………
1. Zero
2. Minimum
3. Maximum
Answer : 3
Q40. The Zener current will be minimum when …………
1. Load current is maximum
2. Load current is minimum
3. Load current is zero
Answer : 1
Multiple Choice Questions and Answers on Solid State
Switching Circuits
Q1. A switch has ………………
1. One state
2. Two states
3. Three states
Answer : 2
Q2. A relay is ……….. switch
1. A mechanical
2. An electronic
3. An electromechanical
Answer : 3
Q3. The switch that has the fastest speed of operation is
………….. switch
1. Electronic
2. Mechanical
3. Electromechanical
Answer : 1
Q4. The most inexpensive switch is ………….. switch
1. Electronic
2. Mechanical
3. Electromechanical
Answer : 1
Q5. The main disadvantage of a mechanical switch is that
it………….
1. Is operated mechanically
2. Is costly
3. Has high inertia
Answer : 3
Q6. When a transistor is driven to saturation, ideally the
output is ………………
1. VCC
2. 0
3. VCC/2
4. 2VCC
Answer : 2
Q7. The maximum speed of electronic switch can be …………..
operations per second
1. 104
2. 10
3. 1000
4. 109
Answer : 4
Q8. A relay is superior to a mechanical switch because it
……………
1. Is relatively inexpensive
2. Does not require moving contacts
3. Combines control with power amplification
Answer : 3
Q9. When a transistor is driven to cut off, ideally the output is
…………..
1. VCC
2. 0
3. VCC/2
4. VCC/3
Answer : 1
Q10. ………………. multivibrator is a square wave oscillator
1. Monostable
2. Astable
3. Bistable
Answer : 2
Q11. An astable multivibrator has ………….
1. One stable state
2. Two stable states
3. No stable state
Answer : 3
Q12. If d.c. supply of 10 V is fed to a differentiating circuit,
then output will be …….
1. 20 V
2. 10 V
3. 0 V
Answer : 3
Q13. If the input to a differentiating circuit is a saw-tooth
wave, then output will be ………….
1. Square
2. Triangular
3. Sine
4. Rectangular
Answer : 4
Q14. A bistable multivibrator has …………..
2. One stable state
3. No stable state
Answer : 1
Q15. If a square wave is fed to a differentiating circuit, the
output will be …………
1. Sine wave
2. Sharp narrow pulses
3. Rectangular wave
4. Triangular wave
Answer : 2
Q16. An integrating circuit is a simple RC series circuit with
output taken across ………
1. Both R and C
2. R
3. C
Answer : 3
Q17. For an integrating circuit to be effective , the RC product
should be ………. the time period of the input wave
1. 5 times greater than
2. 5 times smaller than
3. Equal to
4. At least 10 times greater than
Answer : 4
Q18. A differentiating circuit is a simple RC circuit with
output taken across …………..
1. R
2. C
3. Both R and C
Answer : 1
Q19. A monostable vibrator has …………..
1. No stable state
2. One stable state
Answer : 2
Q20. The multivibrator which generates square wave of its
own is the ………… multivibrator
1. Monostable
2. Bistable
3. Astable
Answer : 3
Q21. For a differentiating circuit to be effective, the RC
product should be ………… the time period of the input wave
1. Equal to
2. 5 times greater than
3. 5 times smaller than
4. At least 10 times greater than
Answer : 4
Q22. When a rectangular voltage waveform is applied to a
capacitor, then the current waveform is ……………
1. Rectangular
2. Sinusoidal
3. Sawtooth
4. Square
Answer : 1
Q23. The positive clipper is that which removes the
…………………. half-cycles of the input voltage.
1. Negative
2. Positive
Answer : 2
Q24. A clamping circuits adds ………………… component to
the signal
1. c.
2. c.
3. both d.c. and a.c.
Answer : 1
Q25. One would find a clamping circuit in ………………..
2. Radio transmitter
3. Radio receiver
4. Television receiver
Answer : 4
Q26. When a transistor is used as an amplifier, it is operated in
the ……………… region
1. Off
2. Saturation
3. Active
Answer : 3
Q27. When the transistor (CE arrangement) is in the cut off
region, the collector current is ……………..
1. ICBO
2. ICEO
3. (β + 1) ICEO
4. IC(sat)
Answer : 2
Q28. A negative clipper removes the ……………… half-cycles
of the input voltage
1. Negative
2. Positive
Answer : 1
Q29. If the input to an integrating circuit is a succession of
alternating positive and negative pulses of very short duration,
the output will be …………… wave
1. Rectangular
2. Triangular
3. Sine
4. Square
Answer : 4
Q30. In a multivibrator, we have ………. feedback.
1. Negative
2. 100 % positive
Answer : 2
Multiple Choice Questions and Answers on FET
MULTIPLE CHOICE QUESTIONS AND
ANSWERS BY SASMITA APRIL 27, 2016
Multiple Choice Questions and Answers on FET ( Field Effect
Transistors )
Q1. A JFET has three terminals, namely …………
1. cathode, anode, grid
2. emitter, base, collector
3. source, gate, drain
Answer : 3
Q2. A JFET is similar in operation to …………. valve
1. diode
2. pentode
3. triode
4. tetrode
Answer : 2
Q3. A JFET is also called …………… transistor
1. unipolar
2. bipolar
3. unijunction
Answer : 1
Q4. A JFET is a ………… driven device
1. current
2. voltage
3. both current and voltage
Answer : 2
Q5. The gate of a JFET is ………… biased
1. reverse
2. forward
3. reverse as well as forward
Answer : 1
Q6. The input impedance of a JFET is …………. that of an
ordinary transistor
1. equal to
2. less than
3. more than
Answer : 3
Q7. In a p-channel JFET, the charge carriers are …………..
1. electrons
2. holes
3. both electrons and holes
Answer : 2
Q8. When drain voltage equals the pinch-off-voltage, then
drain current …………. with the increase in drain voltage
1. decreases
2. increases
3. remains constant
Answer : 3
Q9. If the reverse bias on the gate of a JFET is increased, then
width of the conducting channel …………..
1. is decreased
2. is increased
3. remains the same
Answer : 1
Q10. A MOSFET has …………… terminals
1. two
2. five
3. four
4. three
Answer : 4
Q11. A MOSFET can be operated with ……………..
1. negative gate voltage only
2. positive gate voltage only
3. positive as well as negative gate voltage
Answer : 3
Q12. A JFET has ……….. power gain
1. small
2. very high
3. very small
Answer : 2
Q13. The input control parameter of a JFET is ……………
1. gate voltage
2. source voltage
3. drain voltage
4. gate current
Answer : 1
Q14. A common base configuration of a pnp transistor is
analogous to ………… of a JFET
1. common source configuration
2. common drain configuration
3. common gate configuration
Answer : 3
Q15. A JFET has high input impedance because …………
1. it is made of semiconductor material
2. input is reverse biased
3. of impurity atoms
Answer : 2
Q16. In a JFET, when drain voltage is equal to pinch-off
voltage, the depletion layers ………
1. almost touch each other
2. have large gap
3. have moderate gap
Answer : 1
Q17. In a JFET, IDSS is known as …………..
1. drain to source current
2. drain to source current with gate shorted
3. drain to source current with gate open
Answer : 2
Q18. The two important advantages of a JFET are …………..
1. high input impedance and square-law property
2. inexpensive and high output impedance
3. low input impedance and high output impedance
Answer : 1
Q19. …………. has the lowest noise-level
1. triode
2. ordinary trnsistor
3. tetrode
4. JFET
Answer : 4
Q20. A MOSFET is sometimes called ………. JFET
1. many gate
2. open gate
3. insulated gate
4. shorted gate
Answer : 3
Q21. Which of the following devices has the highest input
impedance?
1. JFET
2. MOSFET
3. Crystal diode
4. ordinary transistor
Answer : 2
Q22. A MOSFET uses the electric field of a ………. to control
the channel current
1. capacitor
2. battery
3. generator
Answer : 1
Q23. The pinch-off voltage in a JFET is analogous to ……….
voltage in a vacuum tube
1. anode
2. cathode
3. grid cut off
Answer : 3
Q25. In class A operation, the input circuit of a JFET is

………. biased
1. forward
2. reverse
3. not
Answer : 2
Q26. If the gate of a JFET is made less negative, the width of
the conducting channel……….
1. remains the same
2. is decreased
3. is increased
Answer : 3
Q27. The pinch-off voltage of a JFET is about ……….
1. 5 V
2. 0.6 V
3. 15 V
4. 25 V
Answer : 1
Q28. The input impedance of a MOSFET is of the order of
………..
1. Ω
2. a few hundred Ω
3. kΩ
4. several MΩ
Answer : 4
Q29. The gate voltage in a JFET at which drain current
becomes zero is called ……….. voltage
1. saturation
2. pinch-off
3. active
4. cut-off
Answer : 2
Q31. In a FET, there are ……….. pn junctions at the sides

1. three
2. four
3. five
4. two
Answer : 4
Q32. The transconductance of a JFET ranges from
……………..
1. 100 to 500 mA/V
2. 500 to 1000 mA/V
3. 0.5 to 30 mA/V
4. above 1000 mA/V
Answer : 3
Q33. The source terminal of a JEFT corresponds to …………..
of a vacuum tube
1. plate
2. cathode
3. grid
Answer : 2
Q34. The output characteristics of a JFET closely resemble the
output characteristics of a ………. valve
1. pentode
2. tetrode
3. triode
4. diode
Answer : 1
Q35. If the cross-sectional area of the channel in n-channel
JEFT increases, the drain current ……….
1. is increased
2. is decreased
3. remains the same
Answer : 1
Q36. The channel of a JFET is between the …………….
1. gate and drain
2. drain and source
3. gate and source
4. input and output
Answer : 2
Q37. For VGS = 0 V, the drain current becomes constant when
VDS exceeds ………
1. cut off
2. VDD
3. VP
4. o V
Answer : 3
Q38. A certain JFET data sheet gives VGS(off) = -4 V. The
pinch-off voltage Vp is ……..
1. +4 V
2. -4 V
3. dependent on VGS
4. data insufficient
Answer : 1
Q39. The constant-current region of a JFET lies between
1. cut off and saturation
2. cut off and pinch-off
3. o and IDSS
4. pinch-off and breakdown
Answer : 4
Q40. At cut-off, the JFET channel is ……….
1. at its widest point
2. completely closed by the depletion region
3. extremely narrow
4. reverse baised
Answer : 2
Q41. A MOSFET differs from a JFET mainly because
………………
1. of power rating
2. the MOSFET has two gates
3. the JFET has a pn junction
Answer : 3
Q42. A certain D-MOSFET is biased at VGS = 0 V. Its data
sheet specifies IDSS = 20mA and VGS(off) = -5 V. The value of the
drain current is …………
1. 20 mA
2. 0 mA
3. 40 mA
4. 10 mA
Answer : 1
Q43. A n-channel D-MOSFET with a positive VGS is operating
in …………
1. the depletion-mode
2. the enhancement-mode
3. cut off
4. saturation
Answer : 2
Q44. A certain p-channel E-MOSFET has VGS(th) = -2V. If
VGS= 0V, the drain current is ……….
1. 0 mA
2. ID(on)
3. maximum
4. IDSS
Answer : 1
Q45. In a common-source JFET amplifier, the output voltage
is …………………
1. 180o out of phase with the input
2. in phase with the input
3. 90o out of phase with the input
4. taken at the source
Answer : 1
Q46. In a certain common-source D-MOSFET
amplifier, Vds =3.2 V r.m. and Vgs = 280 mV r.m.s. The voltage
gain is …………
1. 1
2. 11.4
3. 8.75
4. 3.2
Answer : 2
Q47. In a certain CS JFET amplifier, RD= 1kΩ , RS= 560 Ω
, VDD=10V and gm= 4500 μS. If the source resistor is completely
bypassed, the voltage gain is …………
1. 450
2. 45
3. 2.52
4. 4.5
Answer : 4
Q48. A certain common-source JFET has a voltage gain of 10.
If the source bypass capacitor is removed, ……………….
1. the voltage gain will increase
2. the transconductance will increase
3. the voltage gain will decrease
4. the Q-point will shift
Answer : 3
Q49. A CS JFET amplifier has a load resistance of 10 kΩ ,
RD= 820Ω . If gm= 5mS and Vin= 500 mV, the output signal
voltage is ………..
1. 2.05 V
2. 25 V
3. 0.5 V
4. 1.89 V
Answer : 4
Q50. If load resistance in the above question (Q.49) is removed,
the output voltage will …………
1. increase
2. decrease
3. stay the same
4. be zero
Answer : 1
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Multiple Choice Questions and Answers on SCR
Multiple Choice Questions and Answers on SCR (Silicon
Controlled Rectifiers)
Q1. An SCR has …………….. pn junctions

1. Two
2. Three
3. Four
Answer : 2
Q2. An SCR is a solid state equivalent of …………….
1. Triode
2. Pentode
3. Gas-filled triode
4. Tetrode
Answer : 3
Q3. An SCR has ………….. semiconductor layers
1. Two
2. Three
3. Four
Answer : 3
Q4. An SCR has three terminals viz ……………
1. Cathode, anode, gate
2. Anode, cathode, grid
3. Anode, cathode, drain
Answer : 1
Q5. An SCR behaves as a ……………. switch
1. Unidirectional
2. Bidirectional
3. Mechanical
Answer : 1
Q6. An SCR is sometimes called …………
1. Triac
2. Diac
3. Unijunction transistor
4. Thyristor
Answer : 4
Q7. An SCR is made of ………….
1. Germanium
2. Silicon
3. Carbon
Answer : 2
Q8. In the normal operation of an SCR, anode is ……………
w.r.t. cathode
1. At zero potential
2. Negative
3. Positive
Answer : 3
Q9. In normal operation of an SCR, gate is ………..w.r.t.
cathode
1. Positive
2. Negative
3. At zero potential
Answer : 1
Q10. An SCR combines the features of …………..
1. A rectifier and resistance
2. A rectifier and transistor
3. A rectifier and capacitor
Answer : 2
Q11. The control element of an SCR is ………….
1. Cathode
2. Anode
3. Anode supply
4. Gate
Answer : 4
Q12. The normal way to turn on a SCR is by ……………..
1. Breakover voltage
2. Appropriate anode current
3. Appropriate gate current
Answer : 3
Q13. An SCR is turned off by …………….
1. Reducing anode voltage to zero
2. Reducing gate voltage to zero
3. Reverse biasing the gate
Answer : 1
Q14. An SCR is a ……………….. triggered device
1. Voltage
2. Current
3. Voltage as well as current
Answer : 2
Q15. In an SCR circuit the supply voltage is generally ………..
that of breakover voltage
1. Equal to
2. Less than
3. Greater than
Answer : 2
Q16. When an SCR is turned on, the voltage across it is about
……….
1. Zero
2. 10 V
3. 1 V
4. 1 V
Answer : 4
Q17. An SCR is made of silicon and not germanium because
silicon ………
1. Is inexpensive
2. Is mechanically strong
3. Has small leakage current
4. Is tetravalent
Answer : 3
Q18. An SCR is turned off when …………..
1. Anode current is reduced to zero
2. Gate voltage is reduced to zero
3. Gate is reverse biased
Answer : 1
Q19. In an SCR circuit, the angle of conduction can be
changed by ……….
1. Changing anode voltage
2. Changing gate voltage
3. Reverse biasing the gate
Answer : 2
Q20. If firing angle in an SCR circuit is increased, the output
…………
1. Remains the same
2. Is increased
3. Is decreased
Answer : 3
Q21. If gate current is increased, then anode-cathode voltage at
which SCR closes …………….
1. Is decreased
2. Is increased
3. Remains the same
Answer : 1
Q22. When SCR is OFF, the current in the circuit is
…………….
1. Exactly zero
2. Small leakage current
3. Large leakage current
Answer : 2
Q23. An SCR can exercise control over ………. of a.c. supply
1. Positive half-cycles only
2. Negative half-cycles only
3. Both positive and negative half-cycles
4. Positive or negative half-cycles
Answer : 4
Q24. We can control a.c. power in a load by connecting
…………
1. Two SCRs in series
2. Two SCRs in parallel
3. Two SCRs in parallel opposition
Answer : 3
Q25. When SCR starts conducting, then ……………. loses all
control
1. Gate
2. Cathode
3. Anode
Answer : 1

Multiple Choice Questions and Answers on Power Electronics
Multiple Choice Questions and Answers on Power Electronics
Q1. A Triac has three terminals viz ………………

1. Drain, source, gate
2. Two main terminal and a gate terminal
3. Cathode, anode, gate
Answer : 2
Q2. A triac is equivalent to two SCRs …………..
1. In parallel
2. In series
3. In inverse-parallel
Answer : 3
Q3. A triac is a …………. switch
1. Bidirectional
2. Unidirectional
3. Mechanical
Answer : 1
Q4. The V-I characteristics for a triac in the first and third
quadrants are essentially identical to those of ………………. in
its first quadrant
1. Transistor
2. SCR
3. UJT
Answer : 2
Q5. A triac can pass a portion of …………… half-cycle
through the load
1. Only positive
2. Only negative
Answer : 3
Q6. A diac has ………….. terminals
1. Two
2. Three
3. Four
Answer : 1
Q7. A triac has …………….. semiconductor layers
1. Two
2. Three
3. Four
4. Five
Answer : 3
Q8. A diac has …………… pn junctions
1. Four
2. Two
3. Three
Answer : 2
Q9. The device that does not have the gate terminal is
……………….
1. Triac
2. FET
3. SCR
4. Diac
Answer : 4
Q10. A diac has ……………… semiconductor layers
1. Three
2. Two
3. Four
Answer : 1
Q11. A UJT has ……………….
1. Two pn junctions
2. One pn junction
3. Three pn junctions
Answer : 2
Q12. The normal way to turn on a diac is by ………………..
1. Gate current
2. Gate voltage
3. Breakover voltage
Answer : 3
Q13. A diac is …………………. switch
1. An c.
2. A d.c.
3. A mechanical
Answer : 1
Q14. In a UJT, the p-type emitter is ……………. doped
1. Lightly
2. Heavily
3. Moderately
Answer : 2
Q15. Power electronics essentially deals with control of a.c.
power at …………
1. Frequencies above 20 kHz
2. Frequencies above 1000 kHz
3. Frequencies less than 10 Hz
4. 50 Hz frequency
Answer : 4
Q16. When the emitter terminal of a UJT is open, the
resistance between the base terminal is generally
………………..
1. High
2. Low
3. Extremely low
Answer : 1
Q17. When a UJT is turned ON, the resistance between emitter
terminal and lower base terminal …………….
1. Remains the same
2. Is decreased
3. Is increased
Answer : 2
Q18. To turn on UJT, the forward bias on the emitter diode
should be …………… the peak point voltage
1. Less than
2. Equal to
3. More than
Answer : 3
Q19. A UJT is sometimes called …………. diode
1. Low resistance
2. High resistance
3. Single-base
4. Double-base
Answer : 4
Q20. When the temperature increases, the inter-base
resistance (RBB) of a UJT ………….
1. Increases
2. Decreases
3. Remains the same
Answer : 1
Q22. When the temperature increases, the intrinsic stand off

ratio ……….
1. Increases
2. Decreases
3. Essentially remains the same
Answer : 3
Q23. Between the peak point and the valley point of UJT
emitter characteristics we have ………….. region
1. Saturation
2. Negative resistance
3. Cut-off
Answer : 2
Q24. A diac is turned on by …………………
1. A breakover voltage
2. Gate voltage
3. Gate current
Answer : 1
Q25. The device that exhibits negative resistance region is
………………..
1. Diac
2. Triac
3. Transistor
4. UJT
Answer : 4
Q26. The UJT may be used as ……………….
1. Am amplifier
2. A sawtooth generator
3. A rectifier
Answer : 2
Q27. A diac is simply ………………
1. A single junction device
2. A three junction device
3. A triac without gate terminal
Answer : 3
Q28. After peak point, the UJT operates in the …………….
region
1. Cut-off
2. Saturation
Answer : 3
Q29. Which of the following is not a characteristic of UJT?
1. Intrinsic stand off ratio
3. Peak-point voltage
4. Bilateral conduction
Answer : 4
Q30. The triac is …………….
1. Like a bidirectional SCR
2. A four-terminal device
3. Not a thyristor
4. Answers (1) and (2)
Answer : 1
Multiple Choice Questions and Answers on Electronic
Instruments
Q1. An ammeter is connected in …………….. with the circuit
element whose current we wish to measure
1. Series
2. Parallel
3. Series or parallel
Answer : 1
Q2. A galvanometer in series with a high resistance is called
……………
1. An ammeter
2. A voltmeter
3. A wattmeter
Answer : 2
Q3. An ammeter should have ………….. resistance
1. Infinite
2. Very large
3. Very low
Answer : 3
Q4. A voltmeter is connected in a ………….. with the circuit
component across which potential difference is to be measured
1. Parallel
2. Series
3. Series or parallel
Answer : 1
Q5. A voltmeter should have ………. resistance
1. Zero
2. Very high
3. Very low
Answer : 2
Q6. The sensitivity of a multimeter is given in ……………..
1. Ω
2. Amperes
3. kΩ/V
Answer : 3
Q7. If the full-scale deflection current of a multimeter is 50 μA,
its sensitivity is ……..
1. 10 kΩ/V
2. 100 kΩ/V
3. 50 kΩ/V
4. 20 kΩ/V
Answer : 4
Q8. If a multimeter has a sensitivity of 1000 Ω per volt and
reads 50 V full scale, its internal resistance is ………..
1. 20 kΩ
2. 50 kΩ
3. 10 kΩ
Answer : 2
Q9. A VTVM has ………. input resistance than that of a
multimeter
1. More
2. Less
3. Same
Answer : 1
Q10. The input resistance of a VTVM is about ………..
1. 1000 Ω
2. 10 kΩ
3. 20 kΩ
4. 10 MΩ
Answer : 4
Q11. If the negative potential on the control grid of CRT is
increased, the intensity of spot ………….
1. Is increased
2. Is decreased
3. Remains the same
Answer : 2
Q12. For display of signal pattern ………… voltage is applied
to the horizontal plates of a CRO
1. Sinusoidal
2. Rectangular
3. Sawtooth
Answer : 3
Q13. Two multimeters A and B have sensitivities of 10 kΩ/V
and 30 kΩ/V respectively. Then …………..
1. Multimeter A is more sensitive
2. Multimeter B is more sensitive
3. Both are equally sensitive
Answer : 2
Q14. A galvanometer of resistance G is shunted by a very small
resistance S. The resistance of the resulting ammeter is
………………
1. GS/(G+S)
2. G+S
3. G-S
Answer : 1
Q15. A VTVM is never used to measure …………..
1. Voltage
2. Current
3. Resistance
Answer : 2
Q16. The sensitivity of a voltmeter which uses a 100 μA meter
movement is ……………..
1. 1 kΩ/V
2. 10 kΩ/V
3. 5 kΩ/V
Answer : 2
Q17. What is the total resistance of a voltmeter on the 10 V
range when the meter movement is rated for 50 μA of full-scale
current?
1. 10 kΩ
2. 20 kΩ
3. 200 kΩ
Answer : 3
Q18. The materil used to coat inside the face of CRT is
…………..
1. Carbon
2. Sulphur
3. Silicon
4. Phosphorous
Answer : 4
Q19. When an ammeter is inserted in the circuit, the circuit
current will ………..
1. Increase
2. Decrease
3. Remain the same
Answer : 2
Q20. A series ohmmeter circuit uses a 3 V battery and a 1 mA
meter movement. What is the half-scale resistance for this
movement?
1. 3 kΩ
 kΩ
 kΩ
2. 6 kΩ
Answer : 1
Q21. The most accurate device for measuring voltage is
………….
5. Voltmeter
6. Multimeter
7. CRO
8. VTVM
Answer : 3
Q22. The horizontal plates of a CRO are supplied with
…………. to observe the waveform of signal.
1. Sinusoidal wave
2. Cosine wave
3. Sawtooth wave
Answer : 3
Q23. A CRO is used to measure ………….
1. Voltage
2. Frequency
3. Phase
4. All of above
Answer : 4
Q24. If 2% of the main current is to be passed through a
galvanometer of resistance G, then resistance of the shunt
required is ……….
1. G/50
2. G/49
3. 49 G
4. 50 G
Answer : 2
Q25. Which of the following is likely to have the largest
resistance?
1. Voltmeter of range 10 V
2. Moving coil galvanometer
3. Ammeter of range 1 A
4. A copper wire of length 1 m and diameter 3 mm
Answer : 1
Q26. An ideal ammeter has ………… resistance
1. Low
2. Infinite
3. Zero
4. High
Answer : 3
Q27. The resistance of an ideal voltmeter is …………
1. Low
2. Infinite
3. Zero
4. High
Answer : 2
Q28. To send 10% of the main current through a moving coil
galvanometer of resistance 99 Ω the shunt required is
…………..
1. 11 Ω
2. 9 Ω
3. 100 Ω
4. 9 Ω
Answer : 1
Q29. A voltmeter has a resistance of G ohms and range V volts.
The value of resistance required in series to convert it into
voltmeter of range nV is ……………
1. nG
2. G/n
3. G/(n-1)
4. (n-1)G
Answer : 4
Q30. An ammeter has a resistance of G ohms and range of I
amperes. The value of resistance required in parallel to convert
it into an ammeter of range nI is ………….
1. nG
2. (n-1)G
3. G/(n-1)
4. G/n
Answer : 3
Multiple Choice Questions and Answers on Integrated Circuits
Q1. An IC has …………….. size
1. Very large
2. Large
3. Extremely small
Answer : 3
Q2. ICs are generally made of ………………
1. Silicon
2. Germanium
3. Copper
Answer : 1
Q3. ……………… ICs are the most commonly used
1. Thin films
2. Monolithic
3. Hybrid
Answer : 2
Q4. The most popular form of IC package is ……………..
1. DIL
2. Flatpack
3. TO-5
Answer : 2
Q5. ……………. cannot be fabricated on an IC
1. Transistors
2. Diodes
3. Resistors
4. Large inductors and transformers
Answer : 4
Q6. An audio amplifier is an example of ………………
1. Digital IC
2. Linear IC
3. Both digital and linear IC
Answer : 2
Q7. The active components in an IC are ………….
1. Resistors
2. Capacitors
3. Transistors and diodes
Answer : 3
Q8. We use ……………….. ICs in computers
1. Digital
2. Linear
3. Both digital and linear
Answer : 1
Q9. The SiO2 layer in an IC acts as ………….
1. A resistor
2. An insulating layer
3. Mechanical output
Answer : 2
Q10. ICs are used in ……………
1. Linear devices only
2. Digital devices only
3. Both linear and digital devices
Answer : 3
Q11. A transistor takes …………… inductor on a silicon IC
chip
1. Less space than
2. More space than
3. Same space as
Answer : 1
Q12. The most popular types of ICs are …………..
1. Thin-film
2. Hybrid
3. Thick-film
4. Monolithic
Answer : 4
Q13. Digital ICs process …………….
1. Linear signals only
2. Digital signals only
3. Both digital and linear signals
Answer : 3
Q14. Operational amplifiers use …………..
1. Linear ICs
2. Digital ICs
3. Both linear and digital ICs
Answer : 2
Q15. Which of the following is most difficult to fabricate in an
IC?
1. Diode
2. Transistor
3. FET
4. Capacitor
Answer : 4

Multiple Choice Questions and Answers on Hybrid Parameters
Multiple Choice Questions and Answers on Hybrid Parameters
Q1. Hybrid means ………………
1. Mixed
2. Single
3. Unique
Answer : 1
Q2. There are …………… h parameters of a transistor
1. Two
2. Four
3. Three
Answer: 2
Q3. The h parameter approach gives correct results for
…………
1. Large signals only
2. Small signals only
3. Both small and large signals
Answer: 2
Q4. A transistor behaves as a linear device for ………….
1. Small signals only
2. Large signals only
3. Both small and large signals
Answer : 1
Q5. The parameter hie stands for input impedance in ………..
1. CB arrangement with output shorted
2. CC arrangement with output shorted
3. CE arrangement with output shorted
Answer : 3
Q6. The dimensions of hie parameter are ………..
1. Mho
2. Ohm
3. Farad
Answer : 2
Q7. The hfe parameter is called ……………. in CE
arrangement with output shorted
1. Voltage gain
2. Current gain
3. Input impedance
Answer : 2
Q8. If the operating point changes, the h parameters of
transistor ………..
1. Also change
2. Do not change
3. May or may not change
Answer : 1
Q9. The values of h parameter of a transistor in CE
arrangement are ……………… arrangement
1. The same as for CB
2. The same as for CC
3. Different from that in CB
Answer : 3
Q10. In order to determine hfe and hie parameters of a
transistor, ………… is an a.c. short-circuited
1. Input
2. Output
3. Input as well as output
Answer : 2
Q11. If temperature changes, h parameters of a transistor
………….
1. May or may not change
2. Do not change
3. Also change
Answer : 3
Q12. In CE arrangement, the value of input impedance is
approximately equal to …………..
1. Hie
2. Hoe
3. Hre
Answer : 1
Multiple Choice Questions and Answers on Op-Amp (
Operational Amplifier )
Q1. A differential amplifier ……………..
1. is a part of an Op-amp
2. has one input and one output
3. has two outputs
4. answers (1) and (2)
Answer : 4
Q 2. When a differential amplifier is operated single-ended,
…………
1. the output is grounded
2. one input is grounded and signal is applied to the other
3. both inputs are connected together
4. the output is not inverted
Answer : 2
Q3. In differential-mode, …………….
1. opposite polarity signals are applied to the inputs
2. the gain is one
3. the outputs are of different amplitudes
4. only one supply voltage is used
Answer : 1
Q4. In the common mode, ……………
1. both inputs are grounded
2. the outputs are connected together
3. an identical signal appears on both the inputs
4. the output signal are in-phase
Answer : 3
Q5. The common-mode gain is ………..
1. very high
2. very low
3. always unity
4. unpredictable
Answer : 2
Q6. The differential gain is ………
1. very high
2. very low
3. dependent on input voltage
4. about 100
Answer : 1
Q7. If ADM = 3500 and ACM = 0.35, the CMRR is ……….
1. 1225
2. 10,000
3. 80 dB
Answer : 4
Q8. With zero volts on both inputs, an OP-amp ideally should
have an output ………..
1. equal to the positive supply voltage
2. equal to the negative supply voltage
3. equal to zero
4. equal to CMRR
Answer : 3
Q9. Of the values listed, the most realistic value for open-loop
voltage gain of an OP-amp is ……
1. 1
2. 2000
3. 80 dB
4. 100,000
Answer : 4
Q10. A certain OP-amp has bias currents of 50 μA. The input
offset current is ……..
1. 700 nA
2. 99.3 μA
3. 49.7 μA
4. none of these
Answer : 1
Q11. The output of a particular Op-amp increases 8V in 12μs.
The slew rate is …….
1. 90 V/μs
2. 0.67 V/μs
3. 1.5 V/μs
4. none of these
Answer : 2
Q12. For an Op-amp with negative feedback, the output is
…….
1. equal to the input
2. increased
3. fed back to the inverting input
4. fed back to the noninverting input
Answer : 3
Q13. The use of negative feedback ………
1. reduces the voltage gain of an Op-amp
2. makes the Op-amp oscillate
3. makes linear operation possible
Answer : 4
Q14. Negative feedback ………..
1. increases the input and output impedances
2. increases the input impedance and bandwidth
3. decreases the output impedance and bandwidth
4. does not affect impedance or bandwidth
Answer : 2
Q15. A certain noninverting amplifier has Ri of 1 kΩ and Rf of
100 kΩ. The closed-loop voltage gain is ………
1. 100,000
2. 1000
3. 101
4. 100
Answer : 3
Q16. If the feedback resistor in Q15 (above question) is open,
the voltage gain …….
1. increases
2. decreases
3. is not affected
4. depends on Ri
Answer : 1
Q17. A certain inverting amplifier has a closed-loop voltage
gain of 25. The Op-amp has an open-loop voltage gain of
100,000. If an Op-amp with an open-loop voltage gain of
200,000 is substituted in the arrangement, the closed-loop gain
……..
1. doubles
2. drops to 12.5
3. remains at 25
4. increases slightly
Answer : 3
Q18. A voltage follower ……….
1. has a voltage gain of 1
2. is noninverting
3. has no feedback resistor
4. has all of these
Answer : 4
Q19. The Op-amp can amplify
1. a.c. signals only
2. d.c. signals only
3. both a.c. and d.c. signals
4. neither d.c. nor a.c. signals
Answer : 3
Q20. The input offset current equals the ……….
1. difference between two base currents
2. average of two base currents
3. collector current divided by current gain
4. none of these
Answer : 1
Q21. The tail current of a differential amplifier is …….
1. half of either collector current
2. equal to either collector current
3. two times either collector current
4. equal to the difference in base currents
Answer : 3
Q22. The node voltage at the top of the til resistor is closes to
……….
1. collector supply voltage
2. zero
3. emitter supply voltage
4. tail current times base resistance
Answer : 2
Q23. The tail current in a differential amplifier equals …….
1. difference between two emitter currents
2. sum of two emitter currents
3. collector current divided by current gain
4. collector voltage divided by collector resistance
Answer : 2
Q24. The differential voltage gain of a differential amplifier is
equal to RC divided by …….
1. r’e
2. r’e/2
3. 2r’e
4. RE
Answer : 3
Q25. The input impedance of a differential amplifier equals
r’e times ……
1. β
2. RE
3. RC
4. 2β
Answer : 4
Q26. A common-mode signal is applied to ……….
1. the noninverting input
2. the inverting input
3. both iputs
4. top of the tail resistor
Answer : 3
Q27. The common-mode voltage gain is ………
1. smaller than differentail voltage gain
2. equal to differential voltage gain
3. greater than differential voltage gain
Answer : 1
Q28. The input stage of an Op-amp is usually a ……….
1. differential amplifier
2. class B push-pull amplifier
3. CE amplifier
4. swamped amplifier
Answer : 1
Q29. The common-mode voltage gain of a differential amplifier
is equal to RC divided by ……..
1. r’e
2. 2r’e
3. r’e/2
4. 2RE
Answer : 4
Q30. Current cannot flow to ground through …….
1. a mechanical ground
2. an a.c. ground
3. a virtual ground
4. an ordinary ground
Answer : 3
Multiple Choice Questions and Answers on Digital Electronics
Q1. The binary number 10101 is equivalent to decimal number
…………..
1. 19
2. 12
3. 27
4. 21
Answer : 4
Q2. The universal gate is ………………
1. NAND gate
2. OR gate
3. AND gate
Answer : 1
Q3. The inverter is ……………
1. NOT gate
2. OR gate
3. AND gate
Answer : 1
Q4. The inputs of a NAND gate are connected together. The
resulting circuit is ………….
1. OR gate
2. AND gate
3. NOT gate
Answer : 3
Q5. The NOR gate is OR gate followed by ………………
1. AND gate
2. NAND gate
3. NOT gate
Answer : 3
Q6. The NAND gate is AND gate followed by …………………
1. NOT gate
2. OR gate
3. AND gate
Answer : 1
Q7. Digital circuit can be made by the repeated use of
………………
1. OR gates
2. NOT gates
3. NAND gates
Answer : 3
Q8. The only function of NOT gate is to ……………..
1. Stop signal
2. Invert input signal
3. Act as a universal gate
Answer : 2
Q9. When an input signal 1 is applied to a NOT gate, the
output is ………………
1. 0
2. 1
3. Either 0 & 1
Answer : 1
Q10. In Boolean algebra, the bar sign (-) indicates
………………..
1. OR operation
2. AND operation
3. NOT operation
Answer : 3
Semiconductors & PN Junction Theory Questions and
Answers
Just by going through these short questions and answers, you will
cover a large portion of the chapter itself. And not only that, you
will be far ahead of your competitors.
Q1. What is Fermi level?
The maximum energy that an electron in a metal has at the
absolute zero temperature is called the Fermi level of energy.
Q2. What is the basis for classifying a material as a conductor,
semiconductor, or a dielectric? What is the conductivity of
perfect dielectric?
Conductors possess high conductivity whereas the characteristic
property of insulating materials (or dielectrics) is poor
conductivity. Semiconductors occupy an intermediate position
between conductors and insulators. Though there is no rigid line
separating the conductors from semiconductors and
semiconductors from insulators, but still according to resistivity
the materials of resistivity of the order from 10 -8 to 10-3 , 10-13 to
106 and 106 to 1018 ohm-meters may be classified as conductors,
semiconductors and dielectrics respectively.
Another classification is based on temperature coefficient of
resistivity. Metals have positive temperature coefficient of
resistivity. Semiconductors have small negative temperature
coefficient of resistivity and insulators have large negative
temperature coefficient of resistivity.
Q3. Differentiate semiconductors, conductors and insulators on
the basis of band gap.
The distinction between conductors, insulators and semiconductors
is largely concerned with the relative width of the forbidden energy
gaps in their energy band structures. There is a wide forbidden gap
(more than 5eV) for insulators, narrow forbidden gap (about 1eV)
in case of semiconductors and no forbidden gap in case of
conductors.
Q4. What is the importance of valence shell and valence
electrons?
The outermost shell of an atom is called valence shell and the
electrons in this shell are called valence electrons. Formation of
energy bands occur owing to overlapping of energy levels of these
valence electrons in valence shells. With the decrease in
interatomic distance between the atoms in a crystal, the energy
levels of electrons in outermost shells of atoms overlap to form
energy bands.
Q5. What is the forbidden energy gap? How does it occur?
What is its magnitude for Ge and Si?
The energy gap between the valence band and conduction band is
known as forbidden energy gap. It is a region in which no electron
can stay as there is no allowed energy state. Magnitude of
forbidden energy gap in germanium and silicon is 0.72 eV and
1.12 eV respectively at 300 K and 0.785 eV and 1.21 eV
respectively at absolute zero temperature.
Q6. Is a hole a fundamental particle in an atom?
Hole is not a fundamental particle in an atom. Holes may be
thought of as positive particles, and as such they move through an
electric field in a direction opposite to that of electrons.
Q7. Define a hole in a semiconductor.
When an energy is supplied to a semiconductor a valence electron
is lifted to a higher energy level. The departing electron leaves a
vacancy in the valence band. The vacancy is called a hole. Thus, a
vacancy left in the valence band because of lifting of an electron
from the valence band to conduction band is known as a hole.
Q8. What is hole current?
The movement of the hole (positively charged vacancy in the
valence band) from positive terminal of the supply to negative
terminal through semiconductor constitutes hole current.
Q9. What is intrinsic semiconductor ?
An intrinsic semiconductor is one which is made of the
semiconductor material in the extremely pure form (impurity
content not exceeding one part in 100 million parts of
semiconductors).
Q10. Why silicon and germanium are the two widely used
semiconductor materials?
Because the energy required to release an electron from their
valence band (i.e. to break their covalent bonds ) is very small
(1.12eV for Si and 0.72eV for Ge).
Q11. Which of the two semiconductor materials Si or Ge has
larger conductivity at room temperature? Why?
Since energy required in transferring electrons from valence band
to conduction band is more in case of Si than that in case of
germanium , the conductivity of Ge will be more than that of Si at
room temperature.
Q12. Why does a pure semiconductor behave like an insulator
at absolute zero temperature?
For a pure semiconductor at a temperature of absolute zero (-
273.15oC)the valence band is usually full and there are may be no
electron in the conduction band and it is difficult to provide
additional energy required for lifting electron from valence band to
conduction band by applying electric field. Hence the conductivity
of a pure semiconductor at absolute zero temperature is zero and it
behaves like an insulator.
Q13. What is the main factor for controlling the thermal
generation and recombination?
Temperature, because with the increase in the temperature,
concentrations of free electrons and holes increase and the rate of
recombination is proportional to the product of concentration of
free electrons and holes and also the rate of production of electron-
hole pairs (thermal generation) increases with the rise in
temperature.
Q14. Define mean life of a carrier.
The amount of time between the creation and disappearance of a
free electron is called the life time. It varies from a few
nanoseconds to several microseconds depending how perfect the
crystal is and other factors.
Q15. In which bands do the movement of electrons and holes
take place?
Free electrons move in valence band while holes in valence band.
Q16. What is the mechanism by which conduction takes place
inside the semiconductor?
Conduction occurs in any given material when an applied electric
field causes electrons to move in a desired direction within the
material. This may be due to one or both of two processes, electron
motion and hole transfer. In case of former process, free electrons
in the conduction band move under the influence of the applied
electric field. Hole transfer involves electrons which are still
attached to the atoms i.e. those in valence band.
Q17. What do you mean by drift velocity and mobility of a free
electron?
The average velocity of an electron is known as drift velocity
whereas mobility of an electron is defined as the drift velocity per
unit electric field.
Q18. Define mobility of a carrier. Show that the mobility
constant of electron is larger than that of a hole.
Mobility is defined as the average particle drift velocity per unit
electric field.
The mobility of electrons is more than that of holes because the
probability of an electron having the energy required to move to an
empty state n the conduction band is much greater than the
probability of an electron having the energy required to move to
the empty state in valence band. The mobility of electron is about
double that of a hole.
Q19. Define diffusion current in a semiconductor.
The diffusion of charge carriers is a result of a gradient of carrier
concentration (i.e., the difference of carrier concentration from one
region to another). In this case concentrations of charge carriers
(either electrons or holes ) tend to distribute themselves uniformly
throughout the semiconductor crystal. This movement continues
until all carriers are evenly distributed throughout the material.
This type of movement of charge carriers is called diffusion
current.
Q20. Define drift current in a semiconductor.
The steady flow of electrons in one direction caused by applied
electric field constitutes an electric current, called the drift current.
Q21. What happens to the conductivity of semiconductor with
the rise in temperature? Compare with the conductivity of
metals.
With the increase in temperature, the concentration of charge
carriers increases resulting in increase in conductivity of
semiconductors. The conductivity of metal decreases with the
increase in temperature.
Q22. Why temperature coefficient of resistance of a
semiconductor is negative?
With the increase in temperature, the concentration of charge
carriers (electrons and holes) increases. As more charge carriers
are made available, the conductivity of a pure semiconductor
increases i.e. resistivity of a pure semiconductor decreases with the
rise in temperature i.e. semiconductors have negative temperature
coefficient of resistance.
Q23. What is meant by Fermi level in semiconductor? Where
does the Fermi level lie in an intrinsic semiconductor?
Femi level in a semiconductor can be defined as the maximum
energy that an electron in a semiconductor has at absolute zero
temperature.
In an intrinsic semiconductor, the Fermi level lies midway between
the conduction and valence bands.
Q24. Differentiate between intrinsic semiconductors and
intrinsic semiconductors?
An intrinsic semiconductor is one which is made of the
semiconductor material in its extremely pure form.
When a small amount of impurity is added to a pure semiconductor
crystal during the crystal growth in order to increase its
conductivity, the resulting crystal is called extrinsic
semiconductor.
Q25. Why doping is done in semiconductors?
Intrinsic (or pure ) semiconductor by itself is of little significance
as it has little current conduction capability at ordinary room
temperature. However, if very small amount of impurity (of the
order of one atom per million atoms of pure semiconductor) is
added to it in the process of crystallization, the electrical
conductivity is increased many times.
Q26. Describe the difference between P-type and N-type
semiconductor materials.
When a small amount of trivalent impurity (such as boron, gallium,
indium or aluminium) is added to a pure semiconductor crystal
during crystal growth, the resulting crystal is called a P-type
semiconductor.
When a small amount of pentavalent impurity (such as arsenic,
antimony, bismuth or phosphrous) is added to a pure
semiconductor crystal during crystal growth, the resulting crystal is
called the N-type semiconductor.
Q27. What do you mean by donor and acceptor impurities?
Donor impurities (such as arsenic, antimony, bismuth or
phosphorous) when added to a pure semiconductor lattice , form
N-type extrinsic semiconductor. The pentavalent impurities are
called donor impurities as such impurities donate electrons to the
lattice.
Acceptor impurities (such as boron, gallium, indium or aluminium)
when added to a semiconductor lattice form P-type extrinsic
semiconductor. The trivalent impurities are called acceptor
impurities because such impurities accept electrons from the
lattice.
Q28. Explain the term doping and its need.
The electrical conductivity of intrinsic semiconductor, which has
little current conducting capability at room temperature and so is of
little use, can be increased many times by adding very small
amount of impurity (of the order of one atom per million atoms of
pure semiconductor) to it in the process of crystallization. This
process is called doping.
Q30. What is the effect of temperature on extrinsic
semiconductor?
With the increase in temperature of an extrinsic semiconductor, the
number of thermally generated carriers is increased resulting in
increase in concentration of minority carriers. At temperature
exceeding critical temperature the extrinsic semiconductor behaves
like an intrinsic semiconductor but with higher conductivity.
Q31. What are the charge carriers in P-type and N-type
semiconductors?
Fee electrons in n-type semiconductors and holes in p-type
semiconductors are the charge carriers.
Q32. For the same order of doping, why does n-type
semiconductor exhibit larger conductivity than p-type
semiconductor?
Since the mobility of electrons is higher than that of holes, for
same level of doping, n-type semiconductor exhibits larger
conductivity.
Q33. What is the ratio of majority and minority carriers in
intrinsic and extrinsic semiconductors?
For intrinsic semiconductor the ratio of majority and minority
carriers is Unity.
For extrinsic semiconductor the ratio of majority and minority
carriers is Very large.
Q34. What is a p-n junction?
The contact surface between the layers of p-type and n-type
semiconductor pieces placed together so as to form a p-n junction
is called the p-n junction.
Q35. How do the transition region width and contact potential
across a p-n junction vary with the applied bias voltage?
When the p-n junction is forward biased , the transition region
width is reduced and the contact potential is also reduced with the
increase in applied bias voltage.
When the p-n junction is reverse biased, the transition is widened,
and the contact potential is increased and with the increase in
applied bias voltage.
Q36. Which type of charges present on the two opposite faces
of the junction?
Positive charge on n-side and negative charge on p-side of the
junction.
Q37. What types of carriers are present in space charge
region?
No mobile carrier is present in the space charge region.
Q38. Why is space region called the depletion region?
The region around the junction is completely ionized on formation
of p-n junction. As a result, there are no free electrons on the n-
side nor the holes on the p-side. Since the region around the
junction is depleted of mobile charges, it is called the depletion
region.
Q39. Why an electric field is produced in a depletion region of
a p-n junction?
The separation of positive and negative space charge densities in a
p-n junction results in an electric field.
Q40. What is space charge width?
The space charge region extends into the n and p-regions from the
metallurgical junction. The distance is known as the space charge
width.
Q41. The electric field in the space charge region decreases
with forward bias and increases with reverse bias. Why?
Because applied electric field opposes built-in field.
Q42. Define cut-in voltage of a p-n junction diode?
The forward voltage, at which the current through the p-n junction
starts increasing rapidly, is called the cut-in voltage.
Q43. What do you understand by reverse saturation current of
a diode?
Reverse saturation current of a diode is due to minority carriers
and is caused when the diode is reverse biased. Only a very small
voltage is required to direct all minority carriers across the
junction, and when all minority carriers are flowing across, further
increase in bias voltage will not cause increase in current. This
current is referred to as reverse saturation current.
Q44. What is the effect of temperature on the reverse current
of a p-n junction?
Reverse current of a p-n junction increases with the increase in
junction temperature.
Q45. Why is silicon preferred to germanium in the
manufacturing of semiconductor devices?
Silicon preferred to germanium in the manufacturing of
semiconductor devices because such devices have higher peak
inverse voltage and current ratings and wider temperature range
than germanium ones.
Q46. Define peak inverse voltage?
Peak inverse voltage is the maximum voltage that can be applied to
the p-n junction without damaging the junction. If the reverse
voltage across the junction exceeds its peak inverse voltage(PIV),
the junction may get destroyed owing to excessive heat.
Q47. Define breakdown voltage.
Breakdown voltage is defined as the reverse voltage at which p-n
junction breaks down with sudden rise with reverse current.
Q48. Define the limitations in the operation conditions of a p-n
junction.
Every p-n junction has limiting values of :
 Maximum forward current
 Peak inverse voltage (PIV)
 Maximum power rating
The p-n junction provides satisfactory performance when operated
within these limiting values. The p-n junction diode may get
destroyed due to excessive heat if any of these values are
exceeded.
Junction Diodes Questions and Answers
Q1. What is a pn junction?
The contact surface between the layers of p-type and n-type
semiconductor pieces plated together so as to form a p-n junction
is called the p-n junction.
Q2. Why is silicon preferred over germanium in the
manufacture of semiconductor devices?
The silicon semiconductor devices have, in general, higher PIV
and current ratings and wider temperature range than germanium
semiconductor devices, that’s why silicon is preferred over
germanium in the manufacture of semiconductor devices.
Q3. What does the arrow head represent in the schematic
symbol of a p-n junction?
The arrow head in the schematic symbol of a p-n junction indicates
the direction of conventional current flow when the diode is
forward biased.
Q4. What are the two mechanisms of breakdown in a p-n
junction?
Avalanche and zener breakdown.
Q5. Name the breakdown mechanism in a lightly doped p-n
junction under reverse biased condition.
Avalanche breakdown.
Q6. Name the breakdown mechanism in a highly doped p-n
junction under reverse biased condition.
Zener breakdown.
Q7. What is an ideal diode?
An ideal diode is a two terminal polarity sensitive device that has
zero resistance when it is forward biased and infinite resistance
when reverse biased.
Q8. What is reverse saturation current?
Reverse current of a diode is due to minority carriers and is caused
when the diode is reverse biased. Only a very small voltage is
required to direct all minority carriers across the junction, and
when all minority carriers are flowing across, further increase in
bias voltage will not cause increase in current. This current is
referred to as reverse saturation current.
Q9. Is reverse saturation current of a diode is independent of
reverse bias voltage?
Yes.
Q10. Why is germanium more temperature dependant than
silicon?
Because the reserve saturation current in case of a germanium
diode is approximately 1,000 times larger.
Q11. What is the effect of temperature on the reverse
saturation current of a diode?
Reverse saturation current , theoretically , increases by 8% per oC
for silicon and 11% per oC for germanium. But from experimental
data it is found that that reverse saturation current increases by 7%
per oC for both silicon and germanium. This is because a surface
leakage current component of reverse saturation current is
independent of temperature. Since (1.07)10 =2.0 (approx.), the
reverse saturation current approximately doubles for every 10 oC
rise in temperature.
Q12. What is static resistance of a diode?
The static or dc resistance of a diode is the resistance offered by it
to the direct current . It is defined as the ratio of the diode voltage
and current at the point of interest and is not sensitive to the shape
of the V-I characteristic curve. It decreases with the increase in
diode current or voltage.
Q13. Define dynamic resistance of a p-n junction diode in
forward biased condition.
The resistance offered by a p-n junction diode to the changing
forward current is defined as the dynamic resistance.
AC or dynamic resistance, r = (Small change in forward voltage)
/(Small change in forward current)
Special Purpose Diodes Questions and Answers
Q1. What is a zener diode?
Zener diode is a p-n junction diode specially designed for
operation in the breakdown region in reverse bias condition.
Q2. What is zener voltage?
The voltage at which the zener diode breaks down is called the
zener voltage.
Q3. What is meant by the temperature coefficient?
The effect of temperature on zener voltage is given in terms of
temperature coefficient which is defined as the percentage change
in nominal zener voltage for each degree centigrade of change in
junction temperature.
Q4. What happens to the series current , load current and
zener current when the dc input voltage of a zener regulator
increases?
Zener current and series current increases while the load current
remains unchanged.
Q5. Why is zener diode used as a voltage regulator?
Zener diode has the property of behaving like a dc battery in ‘on’
state (i.e. when the voltage across the zener diode exceeds its zener
voltage rating VZ) . In ‘on’ state , the voltage across zener diode
remains constant until the voltage across it deops less than V Z .
This property of zener diode makes its use as a voltage regulator.
Q6. Explain how zener diode maintains constant voltage across
the load?
Zener diode has the property of behaving like a dc battery in ‘on’
state. If the zener diode is shunted across the load RL and the
voltage across zener diode is more than the zener voltage VZ then
zener diode is on ‘on’ state , and any variation in voltage across the
zener diode due to variations either in supply voltage or in load
resistance is not able to change the output voltage. Thus zener
diode maintains voltage constant across the load.
Q7. What is tunnel diode?
Tunnel diode is a high conductivity two-terminal p-n junction
doped heavily (about 1,000 times higher than a normal diode).
Q8. What is tunneling?
The mechanism of conduction in a semiconductor diode in which
charge carriers (possessing very little energy) punch through a
barrier directly instead of climbing over it is called tunneling.
Q9. What are the applications of tunnel diodes?
Tunnel diodes are used as amplifiers, oscillators or switching
devices, being an exclusive high-frequency component because of
its very fast response inputs.
Q10. What is PIN diode?
PIN is composed of three sections with a high resistivity intrinsic
layer sandwiched between p and n regions. It offers a variable
resistance (decreasing with the increase in the forward current) in
the forward bias mode and infinite resistance in the reverse bias
mode.
Q11. What is a varactor diode?
A varactor diode is a specially fabricated p-n junction with proper
impurity concentration profile and operated under reverse-biased
mode so as to give a variable junction capacitance.
Q12. Which device produces voltage variable capacitor? How
the voltage variable capacitance varies with the change in
voltage across it?
The varactor diode produces voltage variable capacitor. The
junction capacitance of a varactor diode varies inversely as the
square root of the reverse bias voltage in case of alloyed junction
and varies inversely as the cube root of reverse bias voltage for
diffuse junction.
Q13. What is point contact diode?
Point connect diode consists of an n-type germanium or silicon
(preferably germanium) wafer about 1.25 mm square by 0.5 mm
thick, one face of which is soldered to a metal and the other face
has a phosphor bronze or tungsten spring pressed against it.
Because of very low capacitance, point contact diode is very much
suitable for high frequency applications (of the order of 10 GHz).
Q14. What is a step-recovery diode and why is it so called ?
Step-recovery diode is a voltage-dependent variable capacitor
diode with graded doping profile (concentration of charge carriers
decreasing near the junction). Because of step or sudden recovery
from the reverse current ON to reverse current OFF, it is called the
step-recovery diode.
Q15. What is Schottky diode?
Schottky diode is quite different in construction from the normal
p-n junction diode. It has metal (such as gold, silver, platinum ,
molybdenum, chrome or tungsten ) n one side and n-type doped
silicon on the other side of the junction. It has no storage charge.
The junction barrier is called the Schottky barrier.
Q16. Why is Schottky diode called hot-carrier diode?
Since in forward bias operation of the Schottky diode, the electrons
on the n-side gains enough energy to cross the junction and plunge
into the metal with very large energy, they are usually called into
the metal with very large energy, they are usually called hot
carriers and the diode is called hot-carrier diode.
Q17. What is back diode?
Back diode is similar to a tunnel diode except that tunneling effect
is large but only in the reverse direction. This is also called a
unilateral diode.
Q18. What are power diodes?
The power diodes are similar to p-n junction signal or low-power
diodes but have large power-, voltage-, and current-handling
capabilities than those of conventional p-n junction diodes. Power
diodes find many applications in electronics and electrical
engineering circuits.’
Q19. Why the current in power diode varies linearly rather
than exponentially with voltage?
The large magnitude of current in power diodes leads to ohmic
drop that hides the exponential part of the V-I characteristic curve.
Q20. What is photodiode?
Photodiode is a two-terminal semiconductor p-n junction diode
device and is designed to operate with reverse bias.
Q21. How the current is reduced to zero in a photodiode?
The reverse saturation current I0 flowing through a photodiode is
reduced to zero by applying a forward bias voltage of magnitude
equal to barrier potential.
Q22. Photodiode is a photovoltaic device or a photoconductive
device or both?
Photodiode is a photovoltaic device as well as a photoconductive
device. When it is operated with a reverse bias, it is
photoconductive device and when operated without the reverse
bias, it is a photovoltaic device.
Q23. What is meant by LED?
LED stands for Light Emitting Diode.
Q24. What precautions are required to be observed in the use
of LEDs?
LEDs should neither be reverse-biased nor operated near their
maximum current rating. The leads of an LED should never be
bent closer than about 2 mm from the encapsulation.
Bipolar Junction Transistors (BJTs) Questions and Answers
Q1. Explain why an ordinary junction transistor is called
bipolar?
Because the transistor operation is carried out by two types of
charge carriers (majority and minority carriers), an ordinary
transistor is called bipolar.
Q2. Why transistor is called current controlled device?
The output voltage, current or power is controlled by the input
current in a transistor. So it is called the current controlled device.
Q3. What is the significance of the arrow-head in the transistor
symbol?
Arrow head is always marked on the emitter. The direction
indicated the conventional direction of current flow( from emitter-
to-base in case of p-n-p transistor and from base-to-emitter in case
of n-p-n transistor). Generally no arrow head is marked for
collector since its reverse leakage current is always opposite to the
direction of emitter current.
Q4. Discuss the need for biasing the transistor.
For normal operation, base-emitter junction should be forward
biased and the collector-base junction reverse biased. The amount
of bias required is significant for the establishment of the operating
or the Q-point which is dictated by the mode of operation desired.
In case the transistor is not biased properly, it would :
 work inefficiently
 produce distortion in the output signal
 with the change in transistor parameters or temperature rise, the
operating point may shift and the amplifier output will be
unstable.
Q5. What are ‘emitter injection efficiently’ and ‘base transport
factor’ and how do they influence the transistor operation?
The ratio of current of injected carriers at emitter junction to the
total emitter current is called the emitter junction efficiency. The
ratio of collector current to base current is known as transport
factor
i.e. β* = IC/IB
The larger the value of emitter injection efficiency, the larger the
injected carriers at emitter junction and this increases the collector
current. The larger the β* value the larger the injected carriers
across collector junction and hence collector current increases.
Q6. Which of the transistor currents is always the largest?
Which is always the smallest? Which two currents are
relatively close in magnitude?
The emitter current IE is always the largest one. The base current
IB is always the smallest. The collector current IC and emitter
current IE are relatively close in magnitude.
Q7. Why silicon type transistors are more often used than
germanium type?
Because silicon transistor has smaller cut-off current ICBO, small
variations in ICBO due to variations in temperature and high
operating temperature as compared to those in case of germanium
type.
Q8. Why collector is made larger than emitter and base?
Collector is made physically larger than emitter and base because
collector is to dissipate much power.
Q9. Why the width of the base region of a transistor is kept
very small compared to other regions?
Base region of a transistor is kept very small and very lightly
doped so as to pass most of the injected charge carriers to the
collector.
Q10. Why emitter is always forward biased?
Emitter is always forward biased w.r.t base so as to supply
majority charge carriers to the base.
Q11. Why collector is always reverse-biased w.r.t base?
Collector is always reverse-biased w.r.t baseso as to remove the
charge carriers from the base-collector junction.
Q12. Can a transistor be obtained by connecting tow
semiconductor diodes back-to-back?
No. Because in case of two discrete back-to-back connected diodes
there are four doped regions instead of three and there is nothing
that resembles a thin base region between an emitter and a
collector.
Q13. How α and β are related to each other?
α and β are related as below:
α= β/(1+ β) or β= α/(1- α)
Q14. Define beta of a transistor.
The β factor transistor is the common emitter current gain of that
transistor and is defined as the ratio of collector current to the base
current :
Β = IC/IB
Q15. Why is there a maximum limit of collector supply voltage
for a transistor?
Although collector current is practically independent of collector
supply voltage over the transistor operating range, but if VCB is
increase beyond a certain vale collector current IC is eventually
increases rapidly and possibly destroys the device.
Q16. Explain why ICEO >> ICBO?
The collector cut-off current denoted by ICBO is much larger than
ICBO. ICEO is given as :
ICEO = ICBO/(1-α)
Because α is nearly equal to unity (slightly less than unity), ICEO >>
ICBO
Q17. Why CE configuration is most popular in amplifier
circuits?
CE configuration is mainly used because its current, voltage and
power gains are quite high and the ratio of output impedance and
input impedance are quite moderate.
Q18. Why CC configuration is called a voltage buffer? What is
other name?
Because of its high input impedance and low output impedance,
the common collector circuit finds wide application as a buffer
amplifier between a high impedance source and low impedance
load. it is called a voltage buffer. Its other name is emitter
follower.
Q19. What are the main purposes for which a CC amplifier
may be used.
Because of its high input impedance and low output impedance,
the common collector circuit finds wide application as a buffer
amplifier between a high impedance source and low impedance
load.
Q20.Which configuration among CE, CB, CC gives highest
input impedance and no voltage gain?
Common collector configuration has the highest input impedance
and has voltage gain less than unity.
Q21. What do you understand by collector reverse saturation?
In which configuration does it have a greater value?
When input current (IE in case of CB configuration and IB in case
of CE configuration) is zero, collector current IC is not zero
although it is very small. In fact this is the reverse leakage current
or collector reverse saturation current (ICBO or simply ICO in CB
configuration and ICEO in CE configuration). In case of CE
configuration it is much more than that in case of CB
configuration.
Q22. What is meant by operating point?
Quiescent point is a point on the dc load line which represents
VCE and IC in the absence of ac signal and variations in VCE and
IC take place around this point when ac signal is applied.
Q23. Explain how BJT can be used as an amplifier.
A transistor operates as an amplifier by transfer of the current from
low impedance loop to high impedance loop.
Rectifiers Questions and Answers
Q1. What is a dc power supply?
The part of the equipment that converts ac into dc is called dc
power supply.
Q2. What is a rectifier?
A rectifier is a device which converts alternating current (or
voltage) into unidirectional current (or voltage).
Q3. What is PIV of a diode in a rectifier circuit?
Peak Inverse Voltage (PIV) is the maximum possible voltage that
occurs across a diode when it is reverse biased.
Q4. What is the importance of peak inverse voltage?
If the applied voltage in reverse biased condition exceeds peak
inverse voltage (PIV) rating of the diode, then the diode may get
damaged.
Q5. Why half-wave rectifiers are generally not used in dc
power supply?
The type of supply available from half-wave rectifier is not
satisfactory for general power supply. That is why it is generally
not used in dc power supply.
Q6. Why diodes are not operated in the breakdown region in
rectifiers?
In breakdown region, a diode has a risk of getting damaged or
burnt because the magnitude of current flowing through it
increases in an uncontrollable manner. That is why didoes are not
operated in the breakdown region in rectifiers.
Q7. Define ripple as referred to in a rectifier circuit.
The ac component contained in the pulsating output of a rectifier is
known as ripple.
Q8. What is transformer utilization factor?
Transformer utilization factor is defined as the ratio of power
delivered to the load and ac rating of secondary of supply power
transformer.
Q9. The output of a 60Hz full-wave bridge rectifier has a 60 Hz
ripple. It this circuit working properly?
A full-wave rectifier with 60Hz input must have lowest ripple
frequency equal to twice the input frequency i.e. 120Hz. If the
ripple frequency is 60Hz, it means some diodes in the circuit are
not working.
Q10. What is meant by filter?
Filter is a device that converts pulsating output of rectifier into a
steady dc level.
Q11. Why series inductor and L-section filters cannot be used
with half-wave rectifiers?
Series inductor and L-section filters cannot be used with half-wave
rectifiers because operation of series inductor depends upon the
current through it and needs a minimum current to flow at all
times.
Q12. Why capacitor input filter is preferred to choke input
filter?
In capacitor input filter, the dc output is much larger and ripples
are less in comparison to those in choke input filter. So, capacitor
input filter is preferred to choke input filter.
Q13. Why π-filters are not suitable for varying loads?
Voltage regulation in case of π-filters is very poor and, therefore,
π-filters are not suitable for varying loads.
Q14. Why R-C filters are suitable only for light loads?
R-C filters have poor voltage regulation and need adequate
ventilation to dissipate the heat developed in the resistor R. Thus
R-C filters are suitable only for light loads.
Q15. Why is bleeder resistance employed in a filter circuit?
A resistance, called the bleeder resistance, is placed across the
filter ouput, to provide flow of necessary minimum current through
the choke at all time.
Q16. What is the purpose of bleeder resistance in a rectifier
circuit using L-C filter?
Bleeder resistance RB is placed in parallel with the load so as to
maintain a certain minimum current through the choke, even the
load resistor gets open-circuited, and improves filtering action.
Q17. What is meant by voltage regulation of a dc power
supply?
The change in voltage from no-load to full-load condition is known
as voltage regulation.
Q18. Why is it necessary to include voltage stabilizer in a
power supply?
The magnitude of output dc voltage may vary with the variation of
either the input ac voltage or the magnitude of load current. So at
the output of a rectifier-filter combination a voltage stabilizer is
required.
Electrical Wave Filters Questions and Answers
Q1. What are the commonly used filters?
The most commonly used filters are low-pass, high-pass band-
pass, band-reject and all-pass filters.
Q2. What is the difference between active and passive filters?
A passive filter is formed with passive components, such as
resistors, inductors and capacitors while active filters make use of
transistors or op-amps in addition to resistors and capacitors.
Q3. Why are active filters preferred
Active filters are preferred over passive filters because they
provide gain and frequency adjustment flexibility. They pose no
loading problem because of high input impedance and low output
impedance and they are comparatively less expensive.
Q4. What is a low-pass filter?
A filter that provides a constant output from dc upto a cutoff
frequency fC and then passes no signal above that frequency is
called a low-pass filter.
Q5. What is a high-pass filter?
A filter that provides or passes signals above a cutoff frequency
fCis called a high-pass filter. It has a zero gain starting from zero to
a frequency fC and above this frequency the gain is constant.

BJT Amplifiers Questions and Answers
ELECTRONICS QUESTIONS AND
ANSWERS BY SASMITA OCTOBER 6, 2015
BJT Amplifiers Questions and Answers
Q1. What is an amplifier?
The device that amplifies the amplitude of the input signal is called
the amplifier. An amplifier may be defined as a device that
increases the current, voltage or power of an input signal with the
help of a transistor by furnishing the additional power from a
separate source of supply.
Q2. What is meant by small signal amplifier?
When the input signal is quite weak and produces less small
fluctuations in the output current in comparison to its quiescent
value, the amplifier is called the small signal or voltage amplifier.
Q3. What is meant by phase reversal?
In a CE configuration, the output voltage increases in the negative
direction when the input signal voltage increases in the positive
direction and vice-versa. This is called the phase reversal and and
causes a phase difference of 180o between the input signal and
output voltage.
Q4. What is an ac emitter resistance?
The dynamic resistance of the emitter-base junction diode is called
the ac emitter resistance.
Q5. What do you mean by operating point?
The zero signal values of IC and VCEare known as the operating
point. It is called operating point beacue the variations of IC and
VCE take place about this point when signal is applied. It is also
known as the quiescent or Q-point.
Q6. What is transistor biasing?
The proper flow of zero signal collector current and the
maintenance of proper collector emitter voltage during the passage
of signal is called the transistor biasing.
Q7. What is faithful amplification?
The process of raising the strength of a weak signal without any
change in its general shape is referred to as faithful amplification.
Q8. What is the effect of removal of bypass capacitor in a CE
amplifier circuit?
Removal of bypass capacitor in a CE amplifier circuit causes
excessive degeneration in the amplifier circuit and therefore
reduction in voltage gain.
Q9. Why common-collector circuit is known as an emitter
follower?
The CC circuit amplifier is called an emitter follower because in
this circuit the output voltage at the emitter terminal follows the
input signal applied to the base terminal.
Q10. What are the main purposes for which a common-
collector amplifier may be used?
For a common collector amplifier, current gain is as high as for CE
amplifier, voltage gain is less than unity, input resistance is the
highest and the output resistance is the lowest of all the three (CE,
,CC and CB) configurations. This circuit finds wide applications as
a buffer amplifier between a high impedance source and a low
load.
Cathode Ray Oscilloscope (CRO) Questions and Answers
Q1. What is a cathode ray oscilloscope (CRO)?
A CRO is an electronic device with a CRT as its main component
and other associated circuits consisting of a power supply unit, a
sawtooth-wave generator, horizon and vertical amplifiers .
Q2. How is CRO superior to ordinary measuring instruments?
CRO is an electronic device that gives graphical representation of
alternating quantities under examination. The CRO gives very
accurate measurements and is free from the errorsintroduced by the
moving parts. It is also from damping mechanisms and other
inertia containing parts.
Q3. For what vertical and horizontal plates are provide in a
CRO?
Horizontal and vertical plates are provided between electron gun
and screen to deflect the beam according to the input signal.
Q4. For what a triggering circuit is provided in a CRO?
In a CRO, a triggering circuit is provided for synchronising two
types of deflections so that horizontal deflection starts at the same
point of the input vertical signal each time it sweeps.
Q5. What are the essential components of a CRT?
The essential components of a CRT are electron gun, focussing
and accelerating anodes, horizontal and vertical deflection plates,
and evacuated glass envelope with phosphorescent screen.
Q6. For what electron gun assembly is provided in CRT?
The sole function of an electron gun assembly in a CRO is to
provide a narrow and sharply focused electron beam with is
accelerated towards the phosphor screen.
Q7. Why is the grid in a CRO provided with a hole in it?
The hole in a grid of a CRO is provided to allow passage for
electrons through it and concentrate the beam of electrons along
the axis of the tube.
Q8. What is meant by the deflection sensitivity of a CRO?
The deflection sensitivity of a CRO is defined as the vertical
deflection of the beam on the screen per unit deflecting voltage.
Q9. What is meant by the deflection factor of a CRO?
The deflection factor of a CRO is the reciprocal of the deflection
sensitivity.
Q10. What is Astigmatism control?
Astigmatism control is an adjustment that will provide sharp focus
over the entire screen.
Q11. What is graticule?
Graticule is a scale on transparent material that is fitted to the face
of CRT for the purpose of measurement.
Q12. What is aquadag?
Coating of a conducting material, known as aquadag, is provided
over the interior surface of CRT in order to accelerate the electron
beam after passing between the deflation plates and to collect
electrons produced by the secondary emission when electron beam
strikes the screen.
Q13. What is meant by retrace time?
Retrace time is the time required by the electron beam to return to
its original position on a CRT screen after being deflected to the
right by a sawtooth waveform.
Q14. What is sweep time?
Sweep time is time duration during which the beam is swept from
left to right on the screen of a CRT by the linearly increasing
sawtooth voltage.
Q15. What is a Lissajous pattern?
Lissajous pattern is a pattern that results from applying periodic
signals to the deflection plates of a CRO.
Q16. How is focussing achieved?
Focussing is achieved by various sets of plated forming a sort of
electronic lens. In general, there are three sets of plates. Voltages at
anode 1 and 2 are kept fixed while it is variable on the third anode.
By varying the voltage on the third anode, the spot may be
focussed
Electronic Meters Questions and Answers
Q1. What is the difference between an ammeter and a
voltmeter?
Ammeter is a low resistance indicating instrument while the
voltmeter is a high resistance one.
Q2. Why an ammeter should be of very low resistance?
Ammeter, which is connected in series with the circuit carrying the
current under measurement, must be over very low resistance so
that the voltage drop across the ammeter and power absorbed from
the circuit are as low as possible.
Q3. Why a voltmeter should be of very high resistance?
Voltmeter, which is connected in parallel with the circuit across
which the voltage is to be measured, must be of very high
resistance so that the current flowing through the voltmeter and the
power absorbed from the circuit are minimum possible.
Q4. How an ammeter can be changed to a voltmeter?
An ammeter or low range can be converted into a voltmeter by
connecting a high resistance in series with it provided the current
through the series combination is within the range of the ammeter
when connected across the voltage under measurement.
Q5. What happens when an ammeter is connected across the
circuit?
If an ammeter is connected in parallel to the circuit like a
voltmeter, a very high current will flow through it which will
produce such an excessive heat the insulation of the wire carrying
the current will be destroyed. The wire may itself melt away. Thus
the instrument will get damaged.
Q6. What happens when a voltmeter is connected in series with
the circuit?
If a voltmeter is connected in series with the circuit, the circuit
resistance will become too large and consequently a very small
current will flow through it. The instrument will, however, read
almost the same emf acting on the circuit.
Q7. What do you understand by ammeter shunt?
An ammeter shunt is merely a low resistance that is placed across
the coil circuit of the instrument in order to measure fairly large
currents.
Q8. What do you understand by voltmeter multiplier?
Voltmeter multiplier is a high non-inductive resistance connected
in series with the voltmeter coil and is used for increasing the
range of a voltmeter.
Q9. What is the advantage of using Ayrton or universal shunt
in multi-range ammeters?
The advantage of using Ayrton or universal shunt is that it
eliminates the possibility of the meter being in a circuit without a
shunt.
Q10. What is VOM?
The volt-ohm-milliammeter (VOM) is another name of multimeter.
It is also called AVO meter.
Q11. What is a multimeter?
The instrument, which contains a function switch to connect the
appropriate circuits to the d’Arsonval movement, is often called a
multimeter or ampere-volt-ohm (AVO) meter or volt-ohm-
milliammeter (VOM).
Q12. Indicate the various quantities that can be measured with
a multimeter.
Multimeteris used for measument of current (dc as well as ac),
voltage (dc as well as ac) and resistance. With the external source,
high resistance (exceeding 1MΩ),inductance and capacitance can
be measured with this instrument.
Q13. What are the shortcomings of a multimeter?
It may be noted that the ac sensitivity of a half-wave ac meter is
only 45% of the dc sensitivity, therefore, the loading effect is
greater while measuring ac voltages than while measuring
corresponding dc voltages.
The rectifying action depends upon the frequency to some extent
due to capacitance effect and rectifier instruments show lower
readings. Instrument indications may be in error by as much as
0.5% decrease for every 1kHz rise in frequency.
Q14. Where LCR meter is used?
LCR meters are used to measure the values of inductance (L),
capacitance (C) and resistance (R) directly.
Q15. What is Q-meter?
The Q-meter is an instrument designed for measurement of Q-
factor of a coil as well as for the measurement of electrical
properties of coils and capacitors.
Q16. On what principle does a Q-meter operate?
The Q-meter operates on the principle of series resonance i.e,
under resonant condition of an acseries, circuit voltage across the
capacitor is equal to the applied voltage times of Q of the circuit.
Q17. What is Q-factor of the coil?
The ratio of the inductive reactance to the effective resistance of
the coil is called the Q-factor of the coil.
Q18. What are the different parameters that can be measured
using a Q-meter?
The Q-meter is used for measuring Q-factor, inductance, effective
resistance, self-capacitance, bandwidth and capacitance.
Q19. What are the factors which the measurement accuracy of
Q-meter?
 Factors affecting measurement accuracy are:
 Distributed capacitance or self capacitance of the coil.
 Residual inductance of the instrument.
 Conductance of voltmeter.
 Shunt resistor of Q-meter.
Q20. Why the actual Q-factor of the coil is somewhat larger
than the calculated Q-factor?
Calculated value of Q-factor is somewhat smaller than its actual
value because Q-factor measurement includes the losses of the
resonating capacitor, voltmeter and the shunt resistance Rsh.
Number Systems and Codes Questions and Answers
Q1. What is meant by radix (or base) of a number system?
Radix or base of a number system is the number of digits or
distinct symbols it uses to represent various numbers.
Q2. What is a weighted code?
In a weighed code the value of a digit in a 4-bit depends on its
position such as in BCD code.
Q3. What is non-weighted code?
In a non-weighted code, no definite weights are assigned to the
four digit position such as in BCD code.
Q4. What is meant by LSB and MSB?
The right most bit of a binary number is called least-significant bit
(LSB) while the left most bit of a binary number is known as the
most-significant bit (MSB).
Q5. What are octal and hexadecimal systems?
The number systems with base (or radix) 8 and 16 are known as
octal number system and hexadecimal number system respectively.
Q6. What is meant by BCD code?
BCD code is a decimal system with each digit encoded in its
binary equivalent of 4 digits.
Q7. What is an excess-3 code?
Excess-3 code is derived from the natural BCD code by adding
(0011) to each coded number.
Q8. Why hexadecimal code is widely used in digital systems?
It is very convenient to enter binary data in a digital system using
hex code.
Q9. What is the difference between binary code and BCD?
BCD is not a number system like binary. It is a decimal system
with each decimal digit encoded in its binary equivalent. A straight
binary code takes the complete decimal number and represents it in
binary while the BCD code converts each decimal digit to binary
individually.
Q10. State the disadvantage of a 8-4-2-1 code.
BCD requires more bits than straight binary to represent decimal
numbers of more than one digit. This is because BCD does not use
all possible 4-bit groups and is, therefore, inefficient.
Q11. Why is an excess-3 code called an unweighted code?
Since no definite weights can be assigned to the four digit
positions in an excess-3 code, it is an unweighted code.
Q12. Explain the use of excess-3 code.
The key feature of the excess-3 code is that it is self-
complementing code. It means that 1’s complement of the coded
number yields 9’s complementing of the number itself. The self-
complementing property makes the ecess-3 code useful in some
arithmetic operations, because subtraction can be performed using
9’ complement method and 1’s complement can be easily
produced with digital logic circuits by simply inverting each bit.
Q13. What are the advantages of Gray code?
In Gray code if we go from any one decimal number to the next,
only one bit of the Gray code changes. Because of this feature, an
amount of switching is minimized and the reliability of the
switching systems is improved.
Q14. What is an alphanumeric code?
The codes used for representing letters of alphabet, punctuation
marks and other special characters along with numbers are called
alphanumeric codes.
Q15. Which is the most commonly used code for representing
alphanumeric information?
ASCII (American Standard Code for Information Interchange) is
the most widely used alphanumeric code. It is a 7-bit code
Logic Gates and Boolean Algebra Questions and Answers
ELECTRONICS QUESTIONS AND
ANSWERS BY SASMITA OCTOBER 6, 2015
Logic Gates and Boolean Algebra Questions and Answers
Q1. What is Boolean Algebra?
Boolean algebra is a mathematic system of logic in which truth
functions are expresses as symbols and then these symbols are
manipulated to arrive at conclusion.
Q2. What are the basic logic elements?
Basic logic elements are NOT gate, AND gate, OR gate and the
flip-flop.
Q3. What is a truth table?
Truth table is a table that gives outputs for all possible
combinations of inputs to a logic circuit.
Q4. Define positive logic and negative logic.
If the higher of the two voltages represents a 1 and the lower
voltage represents a 0, then the logic is called a positive logic. On
the other hand, if the lower voltage represents a 1 and the higher
voltage a 0, we have a negative logic.
Q5. What is pulse logic system?
A logic system in which a bit is recognized by the presence or
absence of a pulse is called a pulse or dynamic logic system.
Q6. What is an inverter?
An inverter is a logic gate whose output is the inverse or
complement of its input.
Q7. What are the universal logic gates?
Universal gate is a gate that can perform all the basic logical
operations such as NAND and NOR gates.
Q8. What is the specialty of NAND and NOR gates?
The specialty of NAND and NOR gates is that they are universal
gates and can perform all the basic logical operations.
Q9. Why NAND-NAND realization is preferred over AND-OR
realization?
NAND-NAND realization needs only one type of gate(NAND),
that minimizes IC package counter.
Q10. Why is a two-input NAND gate called universal gate?
NAND gate is called universal gate because any digital system can
be implemented with the NAND gate. Sequential and
combinational circuits can be constructed with these gates because
element circuits like flip-flop can be constructed from two NAND
gates connected back-to-back. NAND gates are common in
hardware because they are easily available in the ICs form. A
NAND gate is in fact a NOT-AND gate. It can be obtained by
connecting a NOT gate in the output of an AND gate.
Q12. What is associate law?
Associate law is a low of addition and multiplication and according
to this law grouping of the variable is the ORing or ANDing of
several variables is immaterial and the results obtained are the
same.
Logic Circuits Questions and Answers
Q1. What is a combinational circuit?
In a combinational circuit, the output depends upon present
input(s) only i.e, not dependant on the previous input(s). The
combinational circuit has no memory element. It consists of logic
gates only.
Q2. Write two characteristics of combinational circuits.
The two characteristics of combinational circuits are:
 In combinational circuits, the output exists as long as the input
exists.
 A combinational circuit will always respond in the same
fashion to the input function, when we apply signal to the input
terminal of the combinational logic circuit.
Q3. What is a half-adder?
A logic circuit, that can add two 1-bit numbers and produce
outputs for sum and carry, is called a half-adder.
Q4. What is a full-adder?
A binary adder, which can add two 1-bit binary numbers along
with a carry bit and produces outputs for sum and carry is called a
full-adder.
Q5. What is a flip-flop?
A flip-flop is a basic memory element that is made of an assembly
of logic gates and is used to store 1-bit of information.
Q6. What is a latch?
It is a D-type of flip-flop and stores one bit of data.
Q7. What is an excitation table?
Excitation table gives an information about what should be the
flip-flop inputs if the outputs are specified before and after the
clock pulses.
Q8. What is a state table?
State table consists of complete information about present state,
next state, and outputs of a sequential circuit.
Integrated Circuits Questions and Answers
Q1. What is an IC?
An integrated circuit (IC) is one in which all active and passive
components such as transistor, diodes, resistors, capacitors etc. are
automatically part of a small semiconductor chip.
Q2. Why are ICs so cheap?
ICs are so cheap because of simultaneous production of hundreds
of similar circuits on a small semiconductor wafer.
Q3. Why do ICs need small power for their operation?
ICs need small power due to their small size.
Q4. Why are ICs more reliable than discrete circuits?
ICs are more reliable because of elimination of soldered joints and
need for fewer interconnections.
Q5. What are the advantages of ICs over discrete component
circuits?
The advantages of IC’s over discrete component circuits are
extremely small size, very small weight, very low cost, lower
power consumption, more reliability, easy replacement, increased
operating speed, close matching, improved functional
performance, suitability for small signal operation etc.
Q6. What are the important IC technologies used?
IC technologies used are monolithic, thin- and thick-flim , and
hybrid or multichip.
Q7. What is monolithic IC?
A monolithic IC is one in which all circuit components and their
interconnections are formed on a single thin wafer, called the
substrate.
Q8. Why is SIO2 layer formed over the entire surface in a
monolithic IC?
SIO2 layer is formed over the entire surface so as to prevent the
contamination of the epitaxial layer.
Q9. How is SIO2 layer formed in a monolithic IC?
The SIO2 layer is grown by exposing the epitaxial layer to an
oxygen atmosphere to about 1,000oC.
Q10. In ICs the substrate is not employed as collector. Why?
If in ICs the substrate is employed as collector, all transistors
fabricated on one substrate would have their collectors connected
together.
Q11. Why is the diffusion technique of formation of resistor
most widely used?
The diffused resistors can be processed while diffusing transistors,
so the diffusion technique is the cheapest and, therefore, is most
widely used.
Q12. Why is the plastic DIP IC package most widely used?
The plastic dual-in-line package is much cheaper than other types
of packages and is, therefore, most widely used.
Operational Amplifiers Questions and Answers
Q1. What is an operational amplifier?
An operational amplifier, abbreviated as op-amp, is basically a
multi-stage, very high gain, direct-coupled, negative feedback
amplifier that uses voltage shunt feedback to provide a stabilized
voltage gain.
Q2. State assumptions made for analyzing ideal op-amp.
Assumptions made for analyzing ideal op-amp are :
 Infinite open-loop gain
 Infinite input impedance
 Zero output impedance
 Perfect balance
 Infinite frequency bandwidth
 Infinite slew rate
 Infinite common-mode rejection ratio
 Nil drift of characteristics with temperature
Q3. What is a voltage transfer curve of an op-amp?
The curve drawn between output voltage and input differential
voltage, for an op-amp, keeping voltage gain A constant is known
as voltage transfer curve.
Q4. What are differential gain and common-mode gain of a
differential amplifier?
When the difference of the two inputs applied to the two terminals
of a differential amplifier is amplified, the resultant gain is termed
as differential gain. But when the two input terminals are
connected to the same input source then the gain established by the
differential amplifier is called the common mode gain.
Q5. Define CMRR.
CMRR is defined as the ration of differential voltage gain to
common-mode voltage gain and it is given as CMRR = Ad/Acm
Q6. Why does an op-amp have high CMRR?
High CMRR ensures that the common mode signals such as noise
are rejected successfully and the output voltage is proportional
only to the differential input voltage.
Q7. Why open-loop op-amp configurations are not used in
linear applications?
When an op-amp is operated in the open-loop configuration, the
output either goes to positive saturation or negative saturation
levels or switches between positive and negative saturation levels
and thus clips the output above these levels. So open-loop op-amp
configurations are not used in linear applications.
Q8. List the parameters that should be considered for ac and
dc applications.
The parameters to be considered for dc applications are:
 Input offset voltage
 Input offset current
 Input bias current
 Drift
The parameters to be considered for ac applications are:
 Gain bandwidth product (GBW)
 Rise time
 Slew rate
 Full-power response
 AC noise
Q9. Define offset voltage as applied to an op-amp.
Input offset voltage may be defined as that voltage which is to be
applied between the input terminals to balance the amplifier.
Q10. Give the typical value of bias current for CA741
operational amplifier.
80nA
Q11. Define slew rate.
Slew rate of an op-amp is defined as the maximum rate of change
of output voltage per unit time and is expresses in V/µs.
Q12. What kind of negative feedback is present in a
noninverting op-amp.
Negative voltage-series feedback.
Q13. What is a voltage follower?
Voltage follower is an electronic circuit in which output voltage
tracts the input voltage both in sign and magnitude.
Q14. What are the advantages of using a voltage follower
amplifier?
Voltage follower has three unique characteristics viz. extremely
high input impedance, extremely low output impedance and unity
transmission gain and is , therefore, an ideal circuit device for use
as a buffer amplifier.
Q15. In what way is the voltage follower a special case of the
non-inverting amplifier?
If feedback resistor is made zero or R1 is made ∞(by keeping it
open-circuited) in a noninverting amplifier circuit, voltage follower
is obtained.
Q16. What is an inverting amplifier?
In an inverting amplifier, the input is connected to the minus or
inverting terminal of op-amp.
Q17. What are the applications of an inverting amplifier?
Inverting amplifier is a very versatile component and can be used
for performing number of mathematical stimulation such as analog
inverter, paraphrase amplifier, phase shifter, adder, integrator,
differentiator.
Q18. What is a differential amplifier?
Differential amplifier is a combination of inverting and
noninverting amplifiers and amplifies the voltage difference
between input lines neither of which is grounded.
Q19. Give examples of linear circuits.
Adder, subtractor, differentiator, integrator fall under the category
of linear circuits.
Q20. What is an adder or summing amplifier?
Adder or summing amplifier is a circuit that provides an output
voltage proportional to or equal to the algebraic sum of two or
more input voltages multiplied by a constant gain factor.
Q21. What is an integrator?
An integrator is a circuit that performs a mathematical operation
called integration.
Q22. What are the applications of integrators?
Integrators are widely used in ramp or sweep generators, filters,
analog computers etc.
Q23. Op-amp is used mostly as an integrator than a
differentiator. Why?
Op-amp is used mostly as an integrator than a differentiator
because in differentiator at high frequency, gain is high and so
high-frequency noise is also amplified which absolutely abstract
the differentiated signal.
555 IC Timer Questions and Answers
Q1. What is 555 timer?
The 555 times is a highly stable IC that can produce accurate and
highly stable time delays or oscillation. The frequency of
oscillation and duty cycle are accurately controlled by only two
external resistors and a capacitor.
Q2. What do you mean by a grounded load?
When the load is connected between the output terminal (pin 3)
and grounded terminal (pin 1), it is called grounded load, this is
also sometimes called the normally off load.
Q3. Why normally control terminal of 555 timer is connected
to ground through a 0.01µF bypass capacitor?
Normally control terminal (pin 5) of timer is connected to ground
through a 0.01µF bypass capacitor so as to prevent noise coupled
onto this pin from causing false triggering.
Q4. What are the two basic modes in which the 555 timer
operates?
The 555 timer basically operates in one of the two modes – either
as monostable or as an astable multivibrator.
Q5. Name the CMOS version of the 555 timer.
IC 7555.

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