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Saturday, 27 June 2015

Electrostatics test paper

                            TEST PAPER……………..CLASS - XII PHYSICS
  Electrostatics,class 12, physics test paper ,important questions ,point charge,quepotential surface,

1. Force of attraction between two point electric charges placed at a distance d in a
medium is F. What distance apart should these be kept in the same medium, so that
force between them becomes F/3?[1]

2. The distance of the field point on the equatorial plane of a small electric dipole is
halved. By what factor will the electric filed due to the dipole change?[1]

3. Draw one equipotential surface (1) In a uniform electric field (2) For a point change.

4. If the amount of electric flux entering and leaving a closed surface are 1and 2
respectively. What is the electric charge inside the surface?[2]

5. Derive an expression for the total work done in rotating an electric dipole through an
angle in a uniform electric field?[3]

6. If C1 = 3pF and C2 = 2pF, calculate the equivalent capacitance of the given network
between points A & B?[3]

7prove that energy stored per unit volume in a capacitor is given by 2 1
2 o E , whereE is the electric field of the capacitor?[3]

8. (a) An air capacitor is given a charge of 2C raising its potential to 200 V. If on
inserting a dielectric medium, its potential falls to 50 V, what is the dielectric
constant of the medium?
(b) A conducting stab of thickness‘t’ is introduced without touching between the
plates of a parallel plate capacitor separated by a distance d (t<d). Derive an
expression for the capacitance of a capacitor?[5]

9. The Plates of a charged capacitor are connected by a voltmeter. If the plates of
the capacitor are moved further apart. What will be the effect on the reading of
the voltmeter?[1]

10. What is the function of dielectric in a capacitor? [1]

11. A steam of electrons travelling with speed ms at right angles to a uniform
electric field E is deflected in a circular path of radius r. Prove that ………………………

12. The distance between the plates of a parallel plate capacitor is d. A metal plate
of thickness (d/2) is placed between the plates. What will be the effect on the

13. Keeping the voltage of the charging source constant. What would be the percentage
change in the energy stored in a parallel plate capacitor if the separation between its
plates were to be decreased by 10%?[3]

14. Two identical plane metallic surfaces A and B are kept parallel to each other in air
separated by a distance of 1.0 cm as shown in the figure. Surface A is given a positive
potential of 10V and the outer surface of B is earthed.
(a) What is the magnitude and direction of uniform electric field between point Y
and Z? What is the work done in moving a change of 20 c from point X to Y?
(b) Can we have non-zero electric potential in the space, where electric field
strength is zero?[3]

15. Figure (a) and (b) shows the field lines of a single positive and negative changes
(a) Give the signs of the potential difference : Vp Vq and VB -- VA
(b) Give the sign of the work done by the field in moving a small positive change
from Q to P.
(c) Give the sign of the work done by the field in external agency in moving a

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