M.C.Q : Electrostatics ( 11 to 20)

LEVEL – I

11. Find the charge on an iron particle of mass 2.24 mg, if 0.02 % of electrons are removed from it.

(A) -0.01996

(B) 0.01996 C

(C) 0.02 C

(D) 2.0 C

12. A thick shell with inner radius R and outer radius 3R has a uniform charge density σ c/m3 . It has a spherical cavity of radius R as shown in the figure. The electric field at the centre of the cavity is

(A) zero.

(B) 2σR/εo

(C) 3σR/4εo

(D) 7σR/12εo

13. The electric potential energy of a uniformly charged thin spherical shell of radius R having a total charge Q is ‘

(A) Q2/4πεoR

(B) Q2/6πεoR

(C) Q2/ 8πεoR

(D) Q2/16πεoR

14. Two small metallic spheres each of mass ‘m’ are suspended together with strings of length ‘l’ and placed together. When a quantum of charge ‘q’ is transferred to each the strings make an angle of 90° with each other. The value of ‘q’ is

(A) l √(πεomg)

(B) l √(2πεomg)

(C) l √(4πεomg)

(D) l √(8πεomg)

15. Two concentric spheres of radii R and r have similar charges with equal surface density (σ). The electric potential at their common centre is

(A) σ/εo

(B) (σ/εo)(R-r)

(C) (σ/εo)(R+r)

(D) none of the above

16. Two connected charges of +q and -q respectively are at a fixed distance AB apart in a non uniform electric field whose lines of force are shown in the figure. The resultant effect on the two charges is

(A) a torque in the plane of the paper and no resultant force

(B) a resultant force in the plane of the paper and no torque

(C) a torque normal to the plane of the paper and no resultant force

(D) a torque normal to the plane of the paper and a resultant force in the plane of the paper

17. An electron is accelerating in gravity free region in the absence of an electric field. It will lose its energy in form of

(A) thermal energy

(B) loss in gravitational potential energy

(C) electromagnetic radiations

(D) none of the above

18. A charge +10-9 C is located at the origin in free space and another charge Q at (2, 0, 0). If the X-component of the electric field at (3, 1, 1) is zero. The value of Q is

(A) + 2.4 × 10-10 C

(B) – 6.2 × 10-20 C

(C) – 4.3 × 10-10C

(D) – 1.2 × 10-20 C

19. The figure shows an infinite line charge of density σ C/m. The work done by the electrostatic force on a `unit charge, when it is moved along the path ABC, is (plane of the curve ABC contains the line charge)

(A) zero.

(B) (-σ/2πεo)ln2

(C) (σ/2πεo)ln3

(D) (-σ/2πεo)ln3

20. A charge ‘Q’ is placed at the centre of a hemispherical surface of radius ‘R’. The flux of electric field due to charge ‘Q’, through the surface of hemisphere is

(A) Q/4εo

(B) Q/4πεo

(C) Q/2εo

(D) Q/2πεo

ANSWER:

11. B   12. D   13. C   14. D   15. C   16. D   17. C   18. C   19. D   20. C  

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