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Unit wise Important Questions for CBSE Board Exam
Subject- Physics (Class- XII)
UNIT-I
Q1.
Define the dielectric constant of a medium on the basis of force, electric field and the capacitance?
Q2.
Define dipole, dipole moment and its unit. Also find the electric field due to a dipole on axial and equatorial line.
Q3.
Find an expression for torque acting on an electric dipole placed in a uniform electric field. What is the net force
on the dipole?
Q4.
Find an expression for P.E. of dipole. State the condition for stable and unstable equilibrium.
Q5.
Define electrostatic potential and derive an expression for electric potential at a point due to point charge.
Q6.
Define electrostatic potential energy for two charge system and find an expression for it.
Q7.
State and prove Gauss’s theorem and find the expression for electric field due to
a.
Infinitely long and uniformly charged conductor
b.
Infinitely thin and uniformly charged sheet
c.
Uniformly charged spherical shell
Q8.
Define capacitance and derive an expression for a parallel plate capacitor when the gap between plates is
(a)
fully filled by a dielectric medium
(b)
Partially filled by a dielectric medium
What is the effect on capacitance it the dielectric slab is replaced by conducting slab.
Q9.
Derive an expression for the energy stored in a parallel plate capacitor and also find the energy density. Where
and in which form the energy is stored in a parallel plate capacitor?
Q10. Give principle, construction and working of Vande Graff’s generator. Why the apparatus is enclosed in a steel
chamber?
UNIT-II
Q1.
Define drift velocity and derive an expression for it. What are the factors on which it depends?
Q2.
Define current density. Derive a relation between drift velocity and current flowing through a conductor.
Q3.
State and prove Ohm’s law. What is the effect of temperature on resistance?
Q4.
Define resistivity. What are the factors on which it depends?
Q5.
Define EMF, terminal potential and internal resistance of a cell. Derive a relation between them.
Q6.
Explain grouping of cells (of different e.m.f and internal resistance) in a parallel combination.
Q7.
State Kirchhoff’s laws. Derive the condition for a Wheatstone bridge to be balanced using Kirchhoff’s laws.
Q8.
What is principle of Meter Bridge? How will you find the resistance of a given wire using it? Find the shift in
the balance point when the two resistors in the two gaps are interchanged?
Q9.
Give the principle of a potentiometer and will you use it (a) To compare the e.m.f of two cells and
(b) To find the internal resistance of a primary cell.
How the sensitivity of a potentiometer is increased?
Q10.
A student determining the internal resistance of cell found that the deflection in galvanometer in only in one
direction when jock is moved from one end to another end of potentiometer wire. What may be the two
possible faults for one side deflection?
UNIT-III
Q1.
State Biot- Savart law and find an expression for magnetic filed
(a) At the centre of a circular loop also draw the pattern of magnetic field lines
(b) At the axis of the circular loop.
Q2.
State and prove Ampere’s circuital law and find the magnetic field
(a) Inside a long solenoid
(b) Inside a toroid
(c) Due to an infinitely along straight conductor for r>a and r<a. Also draw the graph for r v/s B
Q3.
Find the force on a straight conductor placed in a uniform magnetic field.
Q4.
Find the expression for the force per unit length acting between two infinitely long straight and parallel
current carrying conductors and hence define one ampere. Also draw the field’s pattern.
Q5.
Derive an expression the torque acting on a rectangular coil suspended freely in a uniform magnetic field.
Q6.
Give principle, construction and working of a moving coil galvanometer with the help of neat and clean
diagram. What is the effect of radial magnetic field?
Q7.
Define current and voltage sensitivity of a galvanometer. State the factors affecting the sensitivity.
Q8.
How will you convert a galvanometer into ammeter and voltmeter for a given range?
Q9.
State the principle, construction and working of a cyclotron. Find the cyclotron frequency and maximum
kinetic energy of ions. Why can’t electron be accelerated in a cyclotron?
Q10.
Name and define the 3 elements required to specify Earth’s magnetic field at a given place. Draw a labelled
diagram to identify these elements.
Q11.
Distinguish between dia, para and ferro magnetic substances in terms of susceptibility, magnetic
permeability, coercivity, behavior in magnetic fields and temperature. Draw the field lines due to an external
magnetic field near a (a) diamagnetic, (b) paramagnetic substance.
Q12.
What are permanent magnets? What is an efficient way of preparing permanent magnets? Write two
characteristic properties of materials which are required to select them for permanent magnets.
Q13.
Define magnetic dipole moment and show that an atom acts as a magnetic dipole.
Q14.
Distinguish the magnetic properties of dia-, para- and ferromagnetic substances in terms of a) susceptibility,
b) magnetic permeability and c) coercivity. Give one example of each of these materials.
Draw the field lines due to an external magnetic field near a i) diamagnetic and a ii) paramagnetic surface.
UNIT IV
Q1.
Define mutual inductance and give its SI unit. Derive expression for the mutual inductance of two long coaxial
solenoids of same length wound one over the other.
Q2.
A coil of number of turns Nand area A is rotated at a constant angular speed ω, in a uniform magnetic field B
and connected to a resistor R. Deduce expressions for maximum e.m.f induced in the coil and the maximum
power dissipated.
Q3.
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.
Q4.
A conducting rod of length l is moved in a magnetic field of magnitude B with velocity v such that the
arrangement is mutually perpendicular. Prove that the e.m.f induced in the coil is lεl = Blv.
Q5.
How are eddy currents produced? Give two applications of eddy currents. Suggest two methods in which the
effect of eddy currents may be minimized.
Q6.
Show that energy stored in an inductor L when a current I0 is established through it is 1/2LI02.
Q7.
With the help of a neat and labelled diagram, explain the principle, construction and working of an AC
generator. A circular coil of N turns and of radius R is kept normal to a magnetic field given by B = B 0cosωt.
Deduce an expression for e.m.f induced in this coil. State the rule which helps to detect the direction of the
induced current.
Q8.
Explain with the help of a labelled diagram, the underlying principle and working of a step –up transformer.
Why cannot such a device be used to step up D.C. voltage? Mention two reasons for energy losses in an
actual transformer.
Q9.
What is a phasor? Draw phasor diagrams showing phase relationship between voltage and current in an ac
circuit containing a) pure inductor only and b) pure capacitor only. Also show graphs of V and I versus time t.
Q10. State the condition under which the phenomenon of resonance occurs in a series LCR circuit. Plot a graph
showing variation of current with frequency of ac source in a series LCR circuit.
Q11. Prove that an ideal inductor/ideal capacitor does not dissipate power in an ac circuit.
Q12. Derive an expression for the impedance and phase difference of an ac circuit consisting of L, C and R in series.
An ac source of voltage V = Vm sinωt, is applied across a series LCR circuit. Draw the phasor diagram for the
circuit when a) the capacitive reactance exceeds the inductive reactance and b) the inductive reactance
exceeds capacitive reactance.
UNIT-V
Q1.
What is meant by the transverse nature of EMW? Draw a diagram showing the propagation of an EM wave
along (a) X-Direction (b) Z- direction, indicating clearly the directions of oscillating electric and magnetic fields
associated with it.
Q2.
Give four characteristics of EM waves. Write the expression for velocity of EMW in terms of permittivity and
permeability of the medium. Give the frequency range and any two uses of the followingsGamma rays, X-rays, UV rays, IR, Micro waves and radio waves.
Q3.
What is the source of EM waves? Which physical if any has the same value for waves belonging to the
different parts of the EM spectrum?
UNIT-VI
Q1.
Derive mirror formula for a concave mirror and convex mirror.
Q2.
Derive an expression for lateral shift and normal shift. On what factors these depend.
Q3.
Define TIR and write the conditions for TIR. Derive a relation between critical angle and the refractive index
of the medium. Also explain the working of isosceles prism and optical fiber.
Q4.
Derive the following relation for a real image formed by a convex refracting surface when the object is placed
in rarer medium. Also write the assumptions and sign convention used.
2
v

1
u

2  1
R
Q5.
Derive the lens maker’s formula. Also write the assumptions and sign convention used.
Q6.
Derive the lens formula for convex lend and concave lens.
Q7.
Derive the relation for equivalent focal length or power when two thin lenses are placed in contact to each
other. In which condition the lens combination will act as a plane glass sheet.
Q8.
Derive the following relations for a prism-
(i)
(ii)
(iii)
i e  A  
  (  1)A
(A   m )
sin
2
 
sin A / 2
Where the symbols have their usual meanings.
Q9.
Draw a ray diagram to show the image formation in refracting type astronomical telescope in the near point
adjustment (when image is formed at LDDV i.e. D=25cm). Derive an expression for its magnifying power. Why
the diameter of objective of telescope should be large.
Q10. Draw a ray diagram to show the image formation in refracting type astronomical telescope in the normal
adjustment (when image is formed at infinity). Derive an expression for its magnifying power. How does the
magnifying power get affected on increasing the aperture of the objective lens and why?
Q11. Draw a ray diagram to show the image formation a compound microscope. Explain briefly the working.
Derive an expression for its magnifying power. Why the diameter of objective of microscope should be small.
Q12. Draw a labelled diagram of a reflecting type telescope. State two advantages of this telescope over refracting
type telescope.
Q13. Define resolving power of compound microscope. How does the resolving power of a compound microscope
change when-(a) Refractive index of medium between the object and objective lens increases (b) Wavelength
of the light used is increased (c) decreasing the diameter of objective (iv) increasing the focal length of its
objective.
Q14. Define the resolving power of astronomical telescope. Write the expression for it and state, on what factors it
depends
Q15. Define wave front. State Huygens principle and verify Snell’s law.
Q16. State Huygens principle and prove the laws of reflection on the basis of wave theory.
Q17. What do you mean by interference of light? Explain in brief the Young’s double slit experiment.
Q18. What are the coherent sources? Write the conditions for the sustained interference pattern. Also draw the
intensity v/s path difference curve.
Q19. Find the conditions for constructive and destructive interference. How does the intensity depend on the
width of slit?
Q20. Find the expression for the fringe width. What is the effect on the fringe width if the whole apparatus (YDSE)
is completely immersed in a liquid of refractive index μ?
Q21. What do you mean by diffraction of light and state the condition for the diffraction? Obtain the conditions for
secondary maxima and minima. Also draw the intensity distribution curve.
Q22. Prove that the width of central maxima is twice the width of the secondary maxima. How does the width of
central maxima depend on the width of the slit?
Q23. State Brewster’s law and prove that the reflected and refracted rays are mutually perpendicular at the angle
of polarization.
Q24. State law of Malus and draw an intensity V/s angle between the plane of transmission of polarizer and
analyzer.
Q25. What are the Polaroids? How are they constructed? Mention their important applications.
Q26. Explain Polarization of light. Give any one method to produce plane polarized light.