# SCC Education

## Electrostatics test paper

TEST PAPER……………..CLASS - XII PHYSICS

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
capacitance?[2]

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