SADHU VASWANI INTERNATIONAL SCHOOL

Kompally

GRADE XII PHYSICS REVISION QUESTIONS

CHAPTER 3
CURRENT ELECTRICITY
1. In the given circuit, assuming point A to be at zero potential, use Kirchhoff’s rules to
determine the potential A at point B.

2. The network PQRS, shown in the circuit diagram, has the

batteries of 4 V and 5 V and negligible internal resistance. A
milliammeter of 20 Ω resistance is connected between P and
R. Calculate the reading in the milliammeter.

3. Use Kirchhoff’s rules to determine the value of the current I1 flowing in the circuit
shown in the figure.

4. Using the concept of drift velocity of charge carriers in a conductor, deduce the
relationship between current density and resistivity of the conductor.
5. Two cells of emfs 1.5 V and 2.0 V having internal resistance 0.2 Ω and 0.3 Ω
respectively are connected in parallel. Derive the formula and Calculate the emf and
internal resistance of the equivalent cell.

6. A battery of emf 12V and internal resistance 2 Ω is connected to a 4 Ω resistor as

shown in the figure.
(a) Show that a voltmeter when placed across the cell and across the resistor, in turn,
gives the
(b) To record the voltage and the current in the circuit, why is voltmeter placed in
parallel and ammeter in series in the circuit?

7. The figure shows a plot of terminal voltage ‘V’ versus the current ‘i’ of a given cell.
Calculate from the graph
(a) emf of the cell and
(b) internal resistance of the cell.

8. A number of identical cells n, each of emf e, internal resistance r connected in series

are charged by a d.c. source of emf elr using a resistor R.
 (i) Draw the circuit arrangement.
(ii) Deduce the expressions for
(a) the charging current and
(b) the potential difference across the combination of the cells.

9. State Kirchhoff’s rules. Use these rules to write the expressions for the current I 1 I2 and
I3 in the circuit diagram shown.

10. Apply Kirchhoff’s rales to the loops ACBPA and ACBQA to write the expressions for the
currents I1, I2 and I3 in the network. (All India 2010)

CHAPTER 4
MOVING CHARGES AND MAGNETISM

1. Derive an expression for the force acting on a current carrying conductor

placed in a uniform magnetic field. Name the rule which gives the direction of
the force. Write the condition for which this force will have (1) maximum (2)
minimum value.
2. A straight wire carries a current of 10A. An electron moving at 10 7 m/s is at
2cm from the wire. Find the force acting on the electron if its velocity is
directed towards the wire.
3. State Biot-Savart's law. Derive an expression for the magnetic field at the
centre of a circular coil of n turns carrying current I.
4. What is a radial magnetic field? How is it obtained in a moving coil
galvanometer?
5. Two straight parallel current carrying conductors are kept at a distance r
from each other in air. The direction for current in both the conductors is the
same. Find the magnitude and direction of the force between them. Hence
define one ampere.
6. A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a
current of 0.40A. What is the magnitude of the magnetic field B at the centre
of the coil?
7. A long straight wire carries a current of 35A. What is the magnitude of the
field B at a point 20 cm from the wire?
 8. A horizontal overhead power line carries a current of 90 A in an east to west
direction. What is the magnitude and direction of the magnetic field due to
the current 1.5 m below the line?
9. What is the magnitude of magnetic force per unit length on a wire carrying a
current of 8 A and making an angle of 300 with the direction of a uniform
magnetic field of 0.15 T ?
10. A 3.0 cm wire carrying a current of 10A is placed inside a solenoid
perpendicular to its axis. The magnetic field inside the solenoid is given to be
0.27 T. What is the magnetic force on the wire?

CHAPTER 5
MAGNETISM AND MATTER
1. Write the expression for the magnetic dipole moment for a closed current
loop. Give its SI unit. Derive an expression for the torque experienced by a
magnetic dipole in a uniform magnetic field.
2. State Gauss’s law for magnetism. Explain Its significance.
3. A short bar magnet placed with its axis at 30° with an external field of 800 G
experiences a torque of 0.016 Nm.
(a) What is the magnetic moment of the magnet?
(b) What is the work done in moving it from its most stable to a most
unstable position? (c) The bar magnet is replaced by a solenoid of
cross-sectional area 2 × 10-4 m² and 1000 turns but of the same magnetic
moment. Determine the current flowing through the solenoid.
4. (a) Define the term magnetic susceptibility and write its relation in terms of
relative magnetic permeability. (b) Two magnetic materials A and B have
relative magnetic permeabilities of 0.96 and 500. Identify the magnetic
materials A and B.
5. Out of the two magnetic materials ‘A’ has relative permeability slightly
greater than unity while ‘B’ has less than unity. Identify the nature of the
materials ‘A’ and ‘B’. Will their susceptibilities be positive or negative?
6. A magnetic needle free to rotate in a vertical plane parallel to the magnetic
meridian has its northern tip down at 60° with the horizontal. The horizontal
component of the earth’s magnetic field at the place is known to be 0.4 G.
Determine the magnitude of the earth’s magnetic field at the place.
7. The susceptibility of a magnetic material is -0.085. Identify the type of
magnetic material. A specimen of this material is kept in a non-uniform
magnetic field. Draw the modified field pattern.
8. A uniform magnetic field gets modified as shown below when two specimens
X and Y are placed in it. State the reason for the behaviour of the field lines

in X and Y.
9. Three identical specimens of magnetic materials nickel, antimony, and
aluminum are kept in a non-uniform magnetic field. Draw the modification
in the field lines in each case. Justify your answer.
10. A bar magnet of the magnetic moment 6 J T1 is aligned at 60° with a
uniform external magnetic field of 0 – 44 T. Calculate
 (a) the work is done in turning the magnet to align its magnetic moment
(i) normal to the magnetic field and
(ii) opposite to the magnetic field .
(b) the torque on the magnet in the final orientation in case (ii).

CHAPTER 6
ELECTROMAGNETIC INDUCTION

1. (i)State Lenz’s law.

(ii) How can the self-inductance of a given coil having ‘N’ number of turns, area
of cross-section of ‘A’ and length T be
increased?
(iii) How does the mutual inductance of a pair of coils change when
(a) the distance between the coils is increased and
(b) the number of turns in the coils is increased?

2. A long straight current-carrying wire passes normally through the centre of the
circular loop. If the current through the wire increases, will there be an
induced emf in the loop? Justify.

3. (i) Predict the polarity of plate A of the capacitor, when a magnet is moved
towards it, as is shown in the figure.

(ii) In the figure given, mark the polarity of plates A and B of a capacitor when
the magnets are quickly moved towards the coil.

4. A long straight current-carrying wire passes normally through the centre of the
circular loop. If the current through the wire increases, will there be an
induced emf in the loop? Justify.
5. An air-cored solenoid has self-inductance 2.8 H. When the core is removed, the
self-inductance becomes 2 mH. What is the relative permeability of the core
used?
6. The figure shows a horizontal solenoid PQ connected to a battery and a switch.
A copper ring R is placed on a frictionless track, the axis of the ring being
along the axis of the solenoid. What would happen to the ring as the switch S
is closed.
 7. In a ceiling fan, each blade rotates in a circle of radius 0.5 m. If the fan makes
2 rotations per second and the vertical component of the earth’s magnetic field
is 8 × 10-5 T, calculate the emf induced between the inner and outer ends of
each blade.
8. A square loop of side 10 cm with its sides parallel to X and Y axes is moved
with a velocity of 8 cm s-1 in the positive X-direction containing a magnetic field
in the positive Z-direction. The field is non-uniform and has a gradient of 10-
3 T cm-1 along the negative X-direction (i.e. it increases by 10-3 T cm-1 as one

move in the negative X-direction). Calculate the emf induced.

9. A circular coil of radius 10 cm, 500 turns and resistance 2 Ω are placed with
its plane perpendicular to the horizontal component of the earth’s magnetic
field. It is rotated about its vertical diameter through 180° in 0.25 s. Estimate
the magnitudes of the emf and the current induced in the coil. The horizontal
component of the earth’s magnetic field at the place is 3.0 × 10 -5 T.

10. A rectangular wire loop of sides 8 cm and 2 cm with a small cut is moving out
of a region of the uniform magnetic field of magnitude 0.3 T directed normal to
the loop. What is the emf developed across the cut if the velocity of the loop is 1
cm s-1 in a direction normal to the (a) longer side, (b) shorter side of the loop?
For how long does the induced voltage last in each case?

11. A 1.0 m long metallic rod is rotated with an angular frequency 400 rad s-1
about an axis normal to the rod passing through its one end. The other end of
the rod is in contact with a circular metallic ring. A constant and uniform
magnetic field of 0.5 T parallel to the axis exists everywhere. Calculate the emf
developed between the centre and the ring.

12. A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical
diameter with an angular speed of 50 rad s -1 in a uniform horizontal magnetic
field of magnitude 3.0 × 10-2 T. Obtain the maximum and average emf induced
in the coil. If the coil forms a closed loop of resistance 10 Ω, calculate the
maximum value of current in the coil. Calculate the average power loss due to
Joule heating. Where does this power come from?
CHAPTER 7
ALTERNATING CURRENT

1. Derivations: rms value and peak value of emf and current

2. Phasor diagrams, Graphs, Inductive reactance, Capacitive reactance
Impedance of LCR series circuit.
3. (a) The peak voltage of an ac supply is 300 V. What is the rms voltage?
(b) The rms value of current in an ac circuit is 10 A. What is the peak current?
(c) A 44 mH inductor is connected to 220 V, 50 Hz ac supply. Determine the
rms value of the current in the circuit.
4. A coil of inductance 0.50 H and resistance 100 Ω is connected to a 240 V, 50
Hz ac supply, (a) What is the maximum current in the coil? (b) What Is the
time lag between the voltage maximum and the current maximum?
5. A coil of 0.01-henry Inductance and 1-ohm resistance is connected to 200
volts, 50 Hz ac supply. Find the Impedance of the circuit and time lag between
max alternating voltage and current.
6. An electrical device draws 2 kW power from AC mains (voltage 223 V (rms) =
V50,000 V). The current differs (lags) in phase by Φ (tan Φ = – 3/4) as
compared to voltage.
Find (i)R (ii) XC – XL (iii) Imean
7. The figure shows a series LCR circuit with L = 5.0 H, C = 80 μF, R = 40 Ω
connected to a variable frequency 240 V source. Calculate

(a) The angular frequency of the source drives the circuit at resonance.
(b) The current at the resonating frequency.
(C) The rms potential drops across the capacitor at resonance.
8. The figure shows a series LCR circuit connected to a variable frequency 200 V
source with L = 50 mH, C = 80 μF and R = 40 Ω.
Determine the source frequency which derives the circuit in resonance;

9. In the following circuit, calculate (a) the capacitance of the capacitor, if the
power factor of the circuit is unity, (b) the Q-factor of this circuit. What is the
significance of the Q-factor in a.c. circuit? Given the angular frequency of the
a.c. source to be 100 s-1. Calculate the average power dissipated in the circuit.
10. The figure below shows how the reactance of a capacitor varies with frequency.

(a) Use the Information on the graph to calculate the value of capacity of the
capacitor.
(b) An inductor of inductance L has the same reactance as the capacitor at 100
Hz. Find the value of L.
(c) Using the same axes, draw a graph of reactance against frequency for the
inductor.
(d) If this capacitor and inductor were connected in series to a resistor of 10 Ω,
what would be the impedance of the combination at 300 Hz?
11. The given graphs (i) and (ii) represent the variation of the opposition offered by
the circuit element to the flow of alternating current, with the frequency of the
applied emf. Identify the circuit element corresponding to each graph.

A circuit is set up by connecting L= 100 mH, C = 5 μf and R =100 Ω in series.

An alternating emf of (150 2–√) volt, (500/π) Hz is applied across this series
combination. Calculate the impedance of the circuit. What is the average power
dissipated in (a) the resistor, (b) the capacitor, (c) the inductor, and (d) the
complete circuit?
12. An ac generator consists of a coil of 50 turns and an area of 2.5 m 2 rotating at
an angular speed of 60 rads-1 in a uniform magnetic field B = 0.2 tesla,
between the two fixed pole pieces. The resistance of the circuit including that of
the coil is 500 ohm (a) Calculate the maximum current drawn from the
generator. (b) What is the flux when the current is zero and (c) Would the
generator work if the coil were stationary and instead the pole pieces rotated
together with the same speed as above? Give a reason for your answer.
13. The output voltage of an ideal transformer, connected to 240 V ac mains, is 24
V. When this transformer is used to light a bulb with rating 24 V, 24 W,
calculate the current in the primary coil of the circuit.
14. The primary coil of an ideal step-up transformer has 100 turns and the
transformation ratio is also 100. The input voltage and the powers are 220 V
and 1100 W respectively. Calculate:
 (a) number of turns in the secondary
(b) the current In the primary
(C) the voltage across the secondary
(d) the current in the secondary
(e) power in the secondary
15. The primary of a transformer has 200 turns and the secondary has 1000
turns. If the power output from the transformer at 1000 V is 9 kW, calculate
(a) The primary voltage and
(b) The heat loss in the primary coil if the resistance of the primary is 0.2 Ω
and the efficiency of the transformer is 90%.

CHAPTER 8
ELECTROMAGNETIC WAVES

1. To which part of the electromagnetic spectrum does a wave of frequency 5 ×

1019 Hz belong?
2. Name the EM waves that are considered suitable for radar systems used in
aircraft navigation? Give reason
3. How is the speed of em-waves in vacuum determined by the electric and
magnetic field?
4. Name the electromagnetic radiations used for
(a) water purification (b) eye surgery (c) Killing bacteria
5. Why are infrared radiations referred to as heat waves also? Name the
radiations which are next to these radiations in the electromagnetic spectrum
having
(a) Shorter wavelength and
(b) Longer wavelength.
6. What physical quantity are the same for X-rays of wavelength 10-10 m, the red
light of wavelength 680 nm, and radio waves of wavelength 500 m?
7. Electromagnetic radiations with wavelength
(a) λ1 are used to kill germs in water purifiers. (b) λ2 are used in TV
communication systems.
(c) λ3 plays an important role in maintaining the earth’s warmth. Name the
part of the electromagnetic spectrum to which these radiations belong.
Arrange these wavelengths in decreasing order of their magnitude.
8. Name the constituent radiation of the electromagnetic spectrum which
(a) is used in satellite communication. (b) is used for studying crystal
structure.
(c) is similar to the radiations emitted during the decay of a radioactive
nucleus.
(d) is absorbed from sunlight by the ozone layer. (e) produces an intense
heating effect
9. Name the radiations of the electromagnetic spectrum which are used in
(a) warfare to look through the haze. (b) radar and geostationary satellites (c)
studying the structure and properties of atoms and molecules.
10. Arrange the following electromagnetic waves in the order of their increasing
wavelength:
(a) Gamma rays
(b) Microwaves
(c) X-rays
(d) Radio waves
11. How are infrared waves produced? What role does infrared radiation play in
(a) maintaining the Earth’s warmth and
(b) physical therapy?

CHAPTER 9
RAY OPTICS

1. Draw a ray diagram to show the formation of an erect image of an object kept
in front of a concave mirror. Hence deduce the mirror formula.
2. Derivation of lens equation
3. Draw a ray diagram to show the formation of the image of an object placed on
the axis of a convex refracting surface, of radius of curvature ‘R’, separating
the two media of refractive indices “n1 and ‘n2‘ (n2 > n1). Use this diagram to
deduce the relation between R and Refractive indices where u and v represent
respectively the distance of the object and the image formed.
4. Lens maker’s formula derivation
5. Magnification by
(a) simple microscope,
(b) compound microscope,
(c) telescope
when final image is at
(i) least distance of distinct vision
(ii) infinity
6. A glass lens of refractive index 1.5 is placed in a trough of liquid. What must
be the refractive index of the liquid in order to mark the lens disappear? OR A
converging lens of refractive index 1.5 is kept in a liquid medium having same
refractive index. What would be the focal length of the lens in this medium?
7. The radii of curvature of the faces of a double convex lens are 10 cm and 15
cm. If focal length of the lens is 12 cm, find the refractive index of the
material of the lens.
8. A biconvex lens has a focal length 2/3 times the radius of curvature of either
surface. Calculate the refractive index of lens material.
9. Find the radius of curvature of the convex surface of a plano-convex lens,
whose focal length is 0.3 m and the refractive index of the material of the lens
is 1.5.
10. Draw a labelled ray diagram of a reflecting telescope. Mention its two
advantages over the refracting telescope
11. A convex lens of focal length 25 cm is placed coaxially in contact with a
concave lens of focal length 20 cm. Determine the power of the combination.
Will the system be converging or diverging in nature?
12. Two monochromatic rays of light are incident normally on the face AB of an
isosceles right angled prism ABC. The refractive indices of the glass prism for
the two rays ‘1’ and ‘2’ are respectively 1.35 and 1.45. Trace the path of these
 rays entering through the prism.

13. A compound microscope uses an objective lens of focal length 4 cm and

eyepiece lens of focal length 10 cm. An object is placed at 6 cm from the
objective lens. Calculate the magnifying power of the compound microscope.
Also calculate the length of the microscope.
14. A convex lens made up of glass of refractive index 1.5 is dipped, in turn,
(i) a medium of refractive index 1.6,
(ii) a medium of refractive index 1.3.
(a) Will it behave as a converging or a diverging lens in the two cases?
(b) How will its focal length change in the two media?
15. A converging lens has a focal length of 20 cm in air. It is made of a material of
refractive index 1.6. It is immersed in a liquid of refractive index 1.3.
Calculate its new focal length.
16. Figure shows an equiconvex lens (of refractive index 1.50) in contact with a liquid layer on top
of a plane mirror. A small needle with its tip on the principal axis is moved along the axis until
its inverted image is found at the position of the needle. The distance of the needle from the
lens is measured to be 45.0 cm. The liquid is removed and the experiment is repeated. The
new distance is measured to be 30.0 cm. What is the refractive index of the liquid?

CHAPTER 10
RAY OPTICS

1. Define the term wavefront. Using Huygen’s wave theory, verify the law of
reflection. Define the term, “refractive index” of a medium. Verify Snell’s law of
refraction when a plane wavefront is propagating from a denser to a rarer
medium.
 2. Explain Interference of light, Describe Young’s double-slit experiment to
produce an interference pattern due to a monochromatic source of light.
Deduce the expression for the fringe width. draw diagram and derive the
expression for positions of maxima and minima. Represent the intensity of the
interference pattern graphically.
3. For yellow light of wavelength 590 nm incident on a glass slab, the refractive
index of glass Is 1.5. Estimate the speed and wavelength of yellow light Inside
the glass slab.
4. What is meant by the diffraction of light? Obtain an expression for the first
minimum of diffraction.
5. Derive an expression for the width of the central maxima for diffraction of light
at a single-slit. How does this width change with an increase in the width of
the slit?
6. Sodium light consists of two wavelengths, 5900 Å and 5960 Å. If a slit of width
2 × 10-4 m is Illuminated by sodium light, find the separation between the first
secondary maxima of the diffraction pattern of the two wavelengths on a screen
placed 1.5m away.
7. The figure drawn here shows the geometry of path differences for diffraction by
a single-slit of width a.

Give appropriate ‘reasoning’ to explain why the intensity of light is

(a) Maximum at the central point C on the screen.
(b) (Nearly) zero for point P on the screen when θ = λ / a.
Hence write an expression for the total linear width of the central maxima on a
screen kept at a distance D from the plane of the slit.
8. What is the effect on the Interference pattern observed In Young’s double-slit
experiment In the following cases:
(a) Screen is moved away from the plane of the slits,
(b) Separation between the slits is Increased and
(c) Widths of the slits are doubled. Give the reason for your answer.
9. Two slits In Young’s double-slit experiment are illuminated by two different
lamps emitting light? Will you observe the Interference pattern? Justify your
answer. Find the ratio of Intensities at two points on a screen In Young’s
double-slit experiment, when waves from two slits have a path difference of (i)
0 and (ii) λ/4.
10. (a) In a single-slit diffraction pattern, how does the angular width of the central
maximum vary, when
(i) the aperture of the slit Is Increased?
(ii) distance between the slit and the screen is decreased?
Justify your answer In each case.
11. In a double-slit experiment using the light of wavelength 600 nm, the angular
width of the fringe formed on a distant screen is 0.1°. Find the spacing between
the two slits.
12. Light of wavelength 5000 A propagating 1n air gets partly reflected from the
surface of the water. How will the wavelengths and frequencies of the reflected
and refracted light be affected?
13. For a single-slit of width, “a” the first minimum of the interference pattern of
monochromatic light of wavelength λ occurs at an angle of λ/a. At the same
angle λ/a, we get a maximum for two narrow slits separated by a distance ‘a’.
Explain.
14. (a) In a single-slit diffraction experiment, the width of the slit is made double
the original width. How does this affect the size and intensity of the central
diffraction band? (b) In what way is diffraction from each slit related to the
interference pattern in a double-slit experiment? (c) When a tiny circular
obstacle is placed in the path of light from a distant source, a bright spot is
seen at the centre of the shadow of the obstacle. Explain why?
15. If one of two identical slits producing interference in Young’s experiment is
covered with glass so that the light intensity passing through it is reduced to
50%, find the ratio of the maximum and minimum intensity of the fringe in the
Interference pattern
CHAPTER 11
DUAL NATURE OF MATTER AND RADIATION
1. Define the term “threshold frequency”, in the context of photoelectric emission.
2. Draw graphs showing the variation of photoelectric current with applied
voltage for two incident radiations of equal frequency and different intensities.
Mark the graph for the radiation of higher intensity.
3. Write the name given to the frequency v0, in the following graph (showing the
variation of stopping potential (Vo) with the frequency (v) of the incident
radiation) for a given photosensitive material. Also name the constant, for that
photosensitive material, obtained by multiplying vc with Planck’s constant.
4. Electrons are emitted from a photosensitive surface when it is illuminated by
green light but electron emission does not take place by yellow light. Will the
electrons are emitted when the surface is illuminated by
(a) red light (b) blue light?
5. The frequency (v) of incident radiation is greater than the threshold frequency
v0 in a photocell. How will the stopping potential vary if frequency (v) is
increased keeping other factors constant?
How much time is taken by a photoelectron to come out of a metal surface,
when the light of wavelength less than threshold wavelength λo is incident on
it?
6. he given graphs show the variation of photoelectric current (l) with the applied
voltage (V) for two different materials and for two different intensities of the
incident radiations. Identify the pairs of curves that correspond to different
materials but the same intensity of incident radiations.
 7. The work function of aluminium is 4.2 eV. If two photons each of energy 2.5 eV
are incident on a surface, will the emission of photoelectron take place?
8. The figure shows a plot of 1V√ where V is the accelerating potential vs the de-
Broglie wavelength λ in case of two particles having the same charge q but
different masses m1 and m2. Which line A or B represents the particle of
greater mass?

9. A proton and a particle are accelerated through the same potential difference.
Which one of the two has
(i) greater de-Broglie wavelength, and
(ii) less kinetic energy? Justify your answer.
10. (a) How does one explain the emission of electrons from a photosensitive
surface with the help of Einstein’s photoelectric equation?
(b) The work function of the following metals is given: Na = 2.75 eV, K = 2.3 eV,
Mo = 4.17eV and Ni = 5.15 eV. Which of these metals will not cause
photoelectric emission for radiation of wavelength 3300 Å from a laser source
placed 1 m away from these metals? What happens if the laser source is
brought nearer and placed 50 cm away?
CHAPTER 14
SEMICONDUCTOR ELECTRONICS
1. Draw the energy band diagram for (a) a p-type semiconductor (b) n-type
semiconductor.
2. Explain formation of p-n junction diode, depletion region and electric field across the
junction.
3. Explain forward bias action and reverse bias action of p-n junction and draw the
characteristics (graphs).
4. Explain dynamic Resistance.
5. Describe the action of p-n junction diode as a rectifier. [ the C-R filter circuit must be
included in diagram and explanation ]
6. Describe with circuit diagrams the fabrication, doping, biasing, working and
characteristics of (a) Photo diode (b) LED (c) Solar cell