Download Question bank Physics Class XII

IMPORTANT 100 QUESTIONS FOR PHYSICS-XII
1. Name the basic properties of electric charges.
2. Give the important properties of electric lines of force.
3. (a) What is an electric dipole? Define electric dipole moment and give its SI unit.
(b)Derive an expression for the torque acting on an electric dipole, when held in a uniform electric field.
Hence define the dipole moment.
4. (a) Define electric flux. Is electric flux a scalar or a vector?
(b)Give the SI units of electric flux?
5. Define electric field intensity and derive an expression for It at a point on the equatorial line of a electric
dipole. Also determine its direction.
6. (a) State Gauss’s theorem in electrostatics. Apply this theorem to calculate the electric field due to a
uniformly charged spherical shell at a point:
(1) Outside the shell,
(2) On the shell, and
(3) Inside the shell.
(b)Draw a graph showing the variation of electric field E with distance r from the centre of a uniformly
charged thin spherical shell.
7. Give some important properties of the equipotential surfaces. Sketch equipotential surfaces for:
(a) A positive point charge.
(b) Two equal and opposite charges separated by a small distance.
(c) Two equal and positive charges separated by a small distance.
A uniform electric field
8. Derive an expression for the electric potential at a distance r from a point charge q.
9. Derive an expression for the electric potential due to an electric dipole on axial line and equatorial line.
10. What are dielectrics? Distinguish between polar and non-polar dielectrics. Give examples.
11. What is a dielectric? A dielectric slab of thickness t is kept between the plates of a parallel plate
capacitor separated by distance d. Derive the expression for the capacitance of the capacitor for t<<d.
12. Derive an expression for the potential energy of a dipole in a uniform electric field. Hence discuss the
conditions of its stable and unstable equilibrium
13. Derive an expression for energy stored in a parallel plate capacitor. On charging a parallel plate capacitor through
a potential V, the spacing between the plate is halved, and a dielectric medium of ----=10 is introduced between the
plates, without disconnecting the dc source.Explain, using suitable expressions, how the i) Capaciatnce, ii)electric
field) energy density of the capacitor change.
14. Establish a relation between current and drift velocity.
15. State kirchoff’s laws for electrical circuits and explain them giving illustrations.
16. Define terminal potential difference of a cell. When a battery of emf Є and internal resistance r is
connected to a resistance R, a current I flows through it. Derive the relation between Є,I,r and R.
17. State the principle of a potentiometer. With the help of a circuit diagram, describe a method to find the
internal resistance of a primary cell.
(b)With the help of a circuit diagram, explain how a potentiometer can be used to compare the emfs of
two primary cells.
18. .(a)What is Wheatstone bridge? State the Wheatstone bridge principle. Deduce the condition for which
the Wheatstone bridge is balanced.
(b)Draw a circuit diagram which can be used to determine the resistance of a given wire also derives the
formula which is used to calculate the unknown resistance.
19. State Biot- Savart law. Write Biot-savart law for the magnetic field due to a current element in vector
form.
20. (a) Using Biot-savart law, derive the expression for the magnetic field due to a current carrying circular
loop of radius ‘a’, at a point which is at a distance ‘r’ from its centre along the axis of the loop.
(b) Discuss the special cases
21. State Ampere’s circuital law. Use Ampere’s law to derive the formula for the magnetic field due to an
infinitely long straight current carrying wire.
22. A long solenoid with closely wound turns has n turns, per unit of its length. A steady current I flow
through this solenoid. Use Ampere’s circuital law to obtain an expression, for the magnetic field, at a point
on its axis and close to its mid point.
23. Derive an mathematical expression for the force per unit length acting on each of the two straight
parallel metallic conductors carrying current in the same direction and kept near each other. Hence define
an ampere. Why do such current carrying conductors attract each other?
24. Derive an expression for the torque on a rectangular coil of area A, carrying a current I and placed in a
magnetic field B. The angle between the direction of B and vector perpendicular to the plane of the coil is
θ.
25. (a) Explain, with the help of a labeled diagram, the principle and construction of a cyclotron. Deduce an
expression for the cyclotron frequency and show that it does not depend on the speed of the charged
particles.
(b) Write limitation and uses of cyclotron.
(c) Write an expression for the maximum kinetic energy acquired by charged particles accelerated by a
cyclotron.
26. With the help of a labeled diagram, explain the underlying principle, construction and working of a
moving coil galvanometer. What is the function of (1) uniform radial field (2) soft iron core; in such a
device? Define current sensitivity and voltage sensitivity of a galvanometer
27. Define with examplesi) Diamagnetic substance
ii) Paramagnetic substance
iii) Ferromagnetic substance
28. (a) Derive an expression for the torque on a magnetic dipole placed in a magnetic field.
(b)When is the torque on a magnet (a) minimum and (b) maximum?
29. (a)Derive an expression for the potential energy of a bar magnet when placed in a uniform magnetic
field. Discuss the special cases.
30. Name and define the various parameters required to completely specify earth’s magnetic field at a
place. Show them in a labeled diagram. Deduce various relations between them.
31. Explain how an atom behaves as a magnetic dipole. Derive an expression for the magnetic dipole
moment of the atom. Also define Bohr magnetron.
32. What are eddy current? Give two applications of eddy currents. How are eddy currents minimized the
energy lose?
33. State Faraday’s laws of electromagnetic induction.
34. State Lenz’s law. Show that Lenz’s law follows from the principle of conservation of energy.
35. Define Motional emf. Prove that the magnitude of the emf induced in a conductor of length l when it
moves at v m/s perpendicular to a uniform magnetic field B is Blv.
36. Write an expression for the energy stored in an inductor when a steady current ‘I’ is passed through it.
Is this energy electric or magnetic?
37.Define self-inductance and give its SI unit. Derive an expression for self-inductance of a long, air-cored
solenoid of length l, radius r and having N number of turns.
38. Define mutual inductance and give its SI unit. Derive an expression for the mutual inductance of two
long coaxial solenoids of same length wound over the other.
39.With the help of a labeled diagram, explain the principle, construction and working of an a.c. generator.
Derive the expression for induced emf.
40. What do you mean by wattles current?
41. What is meant by root mean square or effective value of an alternating current? Derive a relation
between it and its peak value.
42. What do you mean by sharpness of resonance in a series resonant circuit? Find an expression for Qfactor of the circuit.
43. (a) Define power factor of an a.c. circuit.
(b) What are the maximum and minimum values of power factor of an a.c. circuit?
44. Explain with the help of a labeled diagram, the principle, construction and working of a transformer.
Why is its core laminated?
(b) State some of the important uses of transformers.
(c)What are the various energy losses in a transformer? How can they be reduced?
45. Using phasor diagram, derive an expression for the impedance of a series LCR-circuit. What do you
mean by resonance condition of such a circuit?
46. The small ozone layer on top of the stratosphere is crucial for human survival. Why?
47. (a) Distinguish between conduction current and displacement current.
(b) Give the expression for displacement current.
48. Conduction and displacement currents are individually discontinuous, but their sum is continuous.
Comment.
49. What is electromagnetic spectrum? Draw a table, showing different types of electromagnetic waves,
their production and their detection.
50. Derive the mirror formula for concave mirror?
51. Define magnification? Write the expressions for magnification for (a) a concave mirror (b) a convex
mirror. Express m in terms of u,v and f.
52. Define refractive index of a medium in terms of (a) speed of light (b) wavelength of light.
53. Define critical angle for total internal reflection? Derive the relation between the critical angle and the
refractive index of the medium. What is the condition for total internal reflection?
54. State Rayleigh’s law of scattering. Its applications.
55. What is an equivalent lens? Obtain an expression for the effective focal length of two thin lenses placed
in contact coaxially with each other.
56. Derive the lens maker’s formula.
57. Derive the expression for the angle of deviation for a ray of light passing through an equilateral prism of
refracting angle ‘A’. Hence show the relation between refractive index and angle of minimum deviation?
58. Three light rays red, blue and green are incident on a right angled prism abc at face ab .The refractive indices of
the material of the prism for red green and blue wavelengths are 1.39, 1.44and 1.47 respectively. Out of three which
color ray will emerge out of the face ac? Justify your answer. Trace the path of the rays after passing through face ab
59. What is compound microscope? Draw the ray diagram. Write the expression for its magnifying power
when final image is formed at (1) least distance of distinct vision (2) normal adjustment.
60. What is astronomical telescope? Draw the ray diagram. Write the expression for its magnifying power
when final image is formed at (1) least distance of distinct vision (2) normal adjustment.
61. Draw a labeled diagram of a reflecting type telescope. Write advantages of a reflecting type telescope
over a refracting type telescope?
62. What is wave front? Sketch the geometrical shape of the wave front:
(a) Emerging from point source of light.
(b) Corresponding to a beam of light coming from a far away Source.
63. State Huygens’s principle. (a)Using Huygens’s principle show that, for a parallel beam incident on a
reflecting surface, the angle of reflection is equal to the angle of incidence?
(b)Deduce Snell’s law of refraction using Huygens’s wave theory?
64. What are coherent sources of light? State two conditions for two light sources to be coherent? Explain
why two independent sources of light cannot be coherent.
65. What is interference of light? Derive an expression for intensity at any point in young’s double slit
experiment. Hence write the conditions for constructive and destructive interference.
66. State and prove Brewster’s law of polarization.
67. State Mauls law. Draw a graph showing the dependence of intensity of transmitted light on the angle
between polarizer and analyzer.
68. Define the terms with reference to Photo-electric effect.
(a) Work function, (b) Electron emission, (c) Threshold frequency, (d) Stopping potential,
69. What is photoelectric effect? State the laws of photoelectric emission.
70. Explain with graph, the effect of (a) intensity of light on photoelectric current, (b) potential on
photoelectric current, and (c) frequency of incident radiation on stopping potential.
71. Derive the expression for the de Broglie wavelength.
72. Describe Rutherford’s model of the atom? Give its limitation.
73. State Bohr’s postulates for explaining the spectrum of hydrogen atoms. State the drawbacks of Bohr’s
atomic theory.
74. Using Bohr’s postulates, derive an expression for the radii of the permitted orbits in the hydrogen
atom. Also obtain an expression for the total energy of an electron in the nth orbit of an atom. What does
negative value of this energy signify? What is Bohr’s radius?
75. Define activity of a substance. What are the units of activity?
76. Define binding energy and B.E per nucleon. Draw a curve between mass number and average binding energy.
Give the salient features of the curve.
77. Use the law of radioactive disintegration. Using this law, show that the radioactive decay is exponential in
nature?
78. What do you mean by half life and mean life of a radioactive substance? Deduce the relation between them.
79. What is moderator? Explain, why is heavy water used as a moderator in a thermal nuclear reaction?
80. The formation of the energy bands in solids. On the basis of energy band diagrams, distinguish between
(a) a conductor, (b) an insulator and (c) a semiconductor.
81. What are extrinsic semiconductors? Mention their two types.
82. What is p-n junction? Explain with the help of a diagram, how (a) depletion layer, and (b) potential
barrier is formed in a p-n junction diode. Give the circuit symbol for a p-n junction diode.
83. Explain the action of a p-n junction diode in (a) forward bias arrangement and (b) reverse bias
arrangement? Draw its V-I characteristics.
84. Draw a circuit diagram to study the input and output characteristics of an n-p-n transistor in common
emitter configuration. Show these characteristics graphically. Explain how (a) input resistance (b) output
resistance and (c) current amplification factor of the transistor are calculated by using these
characteristics.
85. Explain, with the help of a labeled circuit diagram, the use of n-p-n transistor as a common emitter
amplifier. Write expressions for the various gains of a common emitter amplifier.
86. What is Zener diode? Give its symbol. (b) Sketch and Explain the I-V characteristics of Zener diode. (c)
Explain the use of a Zener diode as a voltage regulator.
87. What is rectifier? Explain, with the help of a circuit diagram, how a p-n junction diode can be used as (a)
half-wave rectifier (b) full-wave rectifier. Draw the input and output waveforms for both.
88. . What is communication system? Describe briefly the major constituents of a communication system
with the help of a block diagram.
89. What do you meant by (a)Ground wave propagation (b)Space wave propagation (c)Sky wave propagation
90. Sky waves are not used in transmitting T.V signals. Why? State two factors by which the range of
transmission of T.V signals can be increased.
91. What is Modulation? What is the need of Modulation in communication systems?
92. Draw the block diagram for production and detection of modulated signal.
93. Give the advantages of Frequency modulation over amplitude modulation.
94. Deduce an expression for the distance up to which the T.V signals can directly be received from a T.V
tower of height h.
95. Write an expression for the maximum line of sight (LOS) distance between two antennas for space
wave propagation.
96. An electron and alpha particle have the same de-Broglie wavelength associated with them. How are their kinetic
energies related to each other?
97. Derive the formula for spherical refracting surface for travelling from denser to the rarer.
98. 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.
99. How does the angle of minimum deviation of glass prism of r.i 1.5 changes, if it is immersed in a liquid of r.i 1.3?
100. Define resistivity. How the resistivity vary with temperature. Write the formula for temperature coefficient of
resistance.