Weekly Exam 1 - DC & Ac Circuits
Weekly Exam 1 - DC & Ac Circuits
Weekly Exam 1 - DC & Ac Circuits
DC and AC Circuits
-------------------------------------------------------------------------------------------------------------------------------------------
Multiple Choice:
17. Find the node voltage VA.
1. You are measuring the current in a circuit that is operated on an 18 V battery. The
ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How
much has the voltage changed?
A. 9 V C. 0 V
B. 900 mV D. 18 V
2. If you wish to increase the amount of current in a resistor from 120 mA to 160 mA
by changing the 24 V source, what should the new voltage setting be?
A. 8 V C. 320 V
B. 3.2 V D. 32 V
A. 6 V C. 4.25 v
3. A 120 V lamp-dimming circuit is controlled by a rheostat and protected from B. 12 V D. 3 V
excessive current by a 3 A fuse. To what minimum resistance value can the
rheostat be set without blowing the fuse? Assume a lamp resistance of 20 ohms. 18. What is the current through R2?
A. 40 W C. 4 W
B. 2 W D. 20 W
4. Which of the following series combinations dissipates the most power when
connected across a 120 V source?
A. 0ne 220 W resistor C. three 220 W resistors
B. two 220 W resistors D. four 220 W resistors
5. All the voltage drops and the source voltage added together in a series circuit is
equal to
A. the total of the voltage drops
B. the source voltage A. 3.19 A C. 1.73 A
C. zero B. 319 mA D. 173 mA
D. the total of the source voltage and the voltage drops
19. What is the voltage drop across R1?
6. To measure the current out of the second resistor in a circuit consisting of four
resistors, an ammeter can be placed:
A. between the second and the third resistors
B. at the negative e terminal of the source
C. between the third and the fourth
D. at any point in the circuit
7. The total resistance of a circuit is 680 W. The percentage of the total voltage
appearing across a 47 W resistor that makes up part of the total series resistance
is?
A. 68% C. 69% A. 850 mV C. 9.18 V
B. 47% D. 6.91% B. 7.82 V D. 918 mV
8. The output of a certain voltage divider is 12 V with no load. When a load is 20. In assigning the direction of branch currents,
connected, the output voltage A. the directions are critical C. they must point into a node
A. decreases C. remains the same’ B. the directions are not critical D. they must point out of a node
B. increases D. becomes zero
21. The branch current method uses:
9. A certain voltage divider consists of two 12 kW resistors in series. Which of the A. KCL and KVL
following load resistors will have the most effect on the output voltage? B. Thevenin’s theorem and Ohm’s law
A. 1 MW C. 18 kW C. KCL and Ohm’s law
B. 24 kW D. 12 kW D. Superposition theorem and Thevenin’s theorem
10. Three 10 kW resistors are connected in series. A 20 kW resistor is connected in 22. One sine wave has a positive-going zero crossing at 15° and another sine wave
parallel across one of the 10 kWresistors. The voltage source is 24 V. The total has a positive-going zero crossing at 55°. The phase angle between the two
current in the circuit is waveforms is:
A. 900 µA C. 90 mA A. 0° C. 70°
B. 9 mA D. 800 µA B. 40° D. none of these
11. A certain voltage divider consists of three 1 k resistors in series. Which of the 23. A square wave has a period of 60 µs. The first odd harmonic is
following load resistors will have the least effect on the output voltage? A. 5 kHz C. 500 kHz
A. 1 MW C. 1 kW B. 50 kHz D. 33.33 kHz
B. 100 kW D. 330 W
24. A phasor represents:
12. The parallel combination of a 470 W resistor and a 1.5 kW resistor is in series A. the magnitude and a quantity direction
with the parallel combination of five 1 kWresistors. The source voltage is 50 V. B. the width of a quantity
The percentage of the load current through any single 1 kW resistor is: C. the phase angle
A. 25% C. 100% D. the magnitude of a quantity
B. 20% D. 50% 25. In a series RC circuit, 12 V(rms) is measured across the resistor and 15 V(rms) is
13. A certain Wheatstone bridge has the following resistor values: R1 = 10 kW, R2 = measured across the capacitor. The rms source voltage is
720 W, and R4 = 2.4 kW. The unknown resistance is A. 3V C. 19.2 V
B. 27 V D. 1.9 V
A. 24W C. 300W
B. 2.4W D. 3,000 W 26. An ac circuit consists of a resistor and a capacitor. To increase the phase angle
above 45°, the following condition must exist:
14. On which of the following voltage range settings will a voltmeter present the
A. R=Xc C. R<Xc
minimum load on a circuit?
B. R>Xc D. R=5Xc
A. 1 V C. 500 v
B. 50 V D. 1,000 V 27. For a certain load, the true power is 150 W and the reactive power is 125 VAR.
The apparent power is
15. When a load resistance is removed from the output of a voltage divider circuit, the
A. 19.52 W C. 275 W
current drawn from the source
B. 195.2 W D. 25 W
A. decreases C. remains the same
B. increases D. is cut off 28. In a series RC circuit, when the frequency and the resistance are halved, the
impedance
16. A 470 W resistor and a 0.2 µF capacitor are in parallel across a 2.5 kHz ac A. doubles
source. The admittance, Y, in rectangular form, is B. is halved
A. 212 W C. 3.14 mS + j2.12 mS C. is reduced to one-fourth
B. 2.12 mS + j3.14 mS D. 318.3 W D. cannot be determined without values
57. An alternating voltage of 80 + j60V is applied to a circuit and the 72. What will be the equation for a 25 cycle current sine wave having
current flowing is –4 + j10A. Find the phase angle. an rms value of 30 A?
A. 25 deg C. 50 deg A. 30 sin 25t C. 20 sin 25t
B. 75 deg D. 100 deg B. 42.5 sin 50pt D. none of these
73. An impedance draws a current I = 10 cos (wt - 30°) from a voltage
58. Calculate the susceptance in mho of a circuit consisting of a
v = 220 sin (wt + 30°). What is the impedance?
resistor of 10 ohms in series with a inductor of 0.1 H when the
A. 15.6 – j15.6 C. 19.1 – j11.1
frequency is 50Hz.
B. 15.6 + j15.6 D. 11.0 + j19.1
A. 0.0303 C. 0.0092
B. –0.029 D. 32.95 74. A series RC circuit is connected to a 230 volt 60 cycle source. If
the power taken by the circuit is 4,800 watts and the voltage drop
59. An inductor of negligible resistance and an inductance of 0.07 H is across the resistor is 115 volts, calculate the capacitance of the
connected in series with a resistor of 20 ohms resistance across a capacitor.
200 V, 50Hz supply. Find the maximum value of energy stored in A. 540 µf C. 530 µf
the coil. B. 556 µf D. 503 µf
A. 3.175 J C. 1.585 J
B. 0.236 J D. 0.33 J 75. A 240 V, 25 Hz sinusoidal generator is connected to a 20 ohms
resistor. Determine the instantaneous current when elapsed time
60. The current taken by a circuit is 1.2 A when the applied voltage is is 0.01 second.
250V and the power taken is 135W. What is the power factor? A. 15043A C. 16.30 A
A. 0.45 C. 0.35 B. 16.97 A D. 12.00 A
B. 0.55 D. 0.65 76. Two current sources deliver current to a common load. The first
source delivers a current whose equation is 25 sin 100πt amperes
61. A capacitor connected to a 115V, 25Hz supply takes 5A. What
while the second delivers a current whose equation is 15 cos
current will it take when the capacitance and frequency are
100πt amperes. What is the ms values of the current in the load?
doubled?
A. 29.15 A C. 40 A
A. 2A C. 5A
B. 20.6 A D. 10 A
B. 10A D. 20A
77. Two sources A and B delivers 100A and 150 A, respectively to a
62. The resistor of 20 ohms is connected in parallel with a capacitor load. If these currents are out of phase by 30 electrical degrees,
across a 110 volt 40Hz supply. If the current taken is 6 A, what is determine the total current drawn by the load.
the capacitance. A. 201.5 A C. 250.0 A
A. 88.6 uF C. 68.8 uF B. 215.4 A D. 241.8 A
B. 86.8 uF D. 76.8 uF
78. Across a 230 V, 60 Hz power supply is a 15-ohm non-inductive
63. A reactor of resistance 20 ohms and inductance of 0.1 H is resistor. What is the equation of the resulting current?
connected in parallel with a capacitor. The value of capacitance to A. 21.68 sin 377t C. 26.55 sin 377 t
produce resonance when connected to a 100V, 50 Hz is ____ B. 15.33 sin 377t D. 28.16 sin 377
A. 71.2 uF C. 1.277uF 79. The ratio of W/VA in an AC Circuit means ______.
B. 17.2 uF D. 72.1 Uf A. Power Factor C. Quality Factor
B. Power Quotient D. Load Factor
64. In an R-L series circuit ac circuit R = 10 ohms and XL = 10 ohms.
The phase angle between the applied voltage and circuit current 80. At what frequency will an inductor of 5 mh have the same
will be reactance as a capacitor of 0.1μF?
A. 45 degrees C. 30 degrees A. 7.12 kHz C. 7.12 Hz
B. 60 degrees D. 36.8 degrees B. 7.12 MHz D. 7.12 GHz
81. In a series RLC circuit
65. A circuit when connected to 200V mains takes a current of 20A,
A. Increasing the frequency decreases the resistance
leading the voltage by 1/12 of time period. The circuit resistance is
B. Increasing the frequency increases the resistance
_______.
C. Both XL and XC change as frequency changes
A. 10 ohms C. 8.66 ohms
D. The frequency at which XL = XC
B. 20 ohms D. 17.32 ohms
82. When the power factor of a circuit is zero ______.
66. An RLC circuit is connected to a 200 V ac source. If the Q factor of A. power absorbed is minimum
the coil is 10, then the voltage across C at resonance is B. power absorbed is maximum
A. 200 V C. 2000V C. power absorbed is zero
B. 20V D. 2V D. the impedance is minimum
67. A circuit has an impedance of (1 –j2) ohms. The susceptance of 83. The power dissipated across the resistance in an AC circuit.
the circuit in mho is A. power factor C. true power
A. 0.1 C. 0.2 B. reactive power D. apparent power
B. 0.4 D. none of these
84. In series RLC circuit, R=100Ω, XL=300Ω, and XC=200Ω. The phase
68. What capacitance must be placed in series with an inductance of angle Ø of the circuit is _____.
0.05 H so that when the frequency is 100Hz, the impedance A. 45 C. 90
becomes equal to the ohmic resistance? B. 180 D. 360
A. 70.5 uF C. 50.7 uF
85. A 220 volt, 60 Hz source is driving a series RL circuit. Determine
B. 5.70 uF D. 7.05 uF
the current in the circuit if R=100Ω and XL = 100Ω.
69. An impedance coil takes 10 A and absorbs 250 W when connected A. 1.10 A (lagging) C. 1.55 A (lagging)
across 220 V, 60 Hz source. What power will it absorb when B. 2.20 A (lagging) D. 4.40 A (lagging)
connected across 110 V, 25 Hz mains?
86. The active and reactive powers of an inductive circuit are equal.
A. 539 W C. 239 W
The power factor of the circuit is _____.
B. 439 W D. 339 W
A. 0.8 lagging C. 0.707 lagging
B. 0.6 lagging D. 0.5 lagging
>>>>>>>>>>>>>>>>>>>NOTHING FOLLOWS<<<<<<<<<<<<<<<<<