PHYSICS
(Electrostatic Force; Field; Field Strength – Dipole)
1. Two electric charges Q and 4Q are separated by a certain distance. If the electric intensity at Q is
E, then the electric intensity at the other charge is
1) 4E 2) E/4 3) E/2 4) 2E
6
2. A bob of a simple pendulum of mass 40 gram with a positive charge 4 10 C is oscillating with
a time period T1 . An electric field of intensity 3.6 104 NC 1 is applied vertically upwards.
T
Now the time period is T2 . If g 10ms 2 , the value of 2 is
T1
1) 0.16 2) 0.64 3) 1.25 4) 0.8
3. The vertices of an equilateral triangle lie on the circumference of a circle of radius 6 cm. Charges
each of 3C are placed at the vertices. If a charge of 1C is placed at the center of the circle, the
force acting on it is
1) 0.75 1013 N 2) 1.5 1013 N 3) 2.25 1013 N 4) zero
4. ‘n’ charges of Q; 4Q; 9Q; 16Q ……………..are placed at distances of 1; 2; 3; 4……… meter
from a point ‘O’ the origin on the same straight line along X-axis. The electric intensity due to the
charges at the origin ‘O’ is
Q Q nQ
1) 2) 3) Infinity 4)
4 0 n 2
4 0 n 4 0
5. In the figure, particles 1 and 2 are fixed in place, but particle 3 is free to move. If the net
q
electrostatic force on particle 3 due to the particles 1 and 2 is zero and L23 2( L12 ) , the ratio 1
q2
1) 2 2) 2.25 3) 2.25 4) 2
6. A particle of mass 2 Kg and charge 1 mC is projected vertically with a velocity 10 m/s. There is a
uniform horizontal electric field of 104 NC 1 . Then
1) the horizontal range of the particle is 10m 2) the time of flight of the particle is 2s
3) the maximum height reached is 5m 4) the horizontal range of the particle is
zero.
7. Two spherical conductors B and C having equal radii and carrying equal charges on them repel
each other with a force F when kept apart at some distance. A third spherical conductor, having
the same radius as that of B but uncharged, is brought in contact with B and then in contact with C
and finally removed away from both. The new force of repulsion between B and C is
1) F/4 2)3F/4 3)F/8 4) 3F/8
8. Let 0 denote the dimensional formula of the permittivity of vacuum. If M = mass, L = length,
T = time and A = electric current, then
1) 0 M 1L3T 4 A2 2) 0 M 1L2T 1 A2
3) 0 M 1L2T 1 A 4) 0 M 1L3T 2 A
9. Four charges equal to Q are placed at the four corners of a square and a charge ‘q’ is placed at
its center. If the system is in equilibrium, the value of ‘q’ is
Q
1) 1 2 2
4
2)
Q
4
1 2 2 Q
3) 1 2 2
2
4)
Q
2
1 2 2
10. Two point charges + 8q and - 2q are located at x = 0 and x = L respectively. The location of a
point on the x-axis at which the net electric field due to these two point charges is zero is
1) 2 L from x = 0 2) L/4 from x = 0 3) 8 L from x = 0 4) L from x = 0
11. Three positive charges of equal value ‘q’ are placed at the vertices of an equilateral triangle. The
resulting lines of force should be sketched as in
1) 2) 3) 4)
12. 2 Cand 6 C two charges are repelling each other with a force of 12 N . If each charge is given 2C
of charge, then the value of the force will be
1) 4 N (Attractive) 2) 4 N (Repulsive) 3) 8 N (Repulsive) 4) Zero
13. Two charges q 1 and q 2 are placed in vacuum at a distance d and the force acting between them is F
. If a medium of dielectric constant 4 is introduced around them, the force now will be
F F
(a) 4F (b) 2F (c) (d)
2 4
14. A sphere carrying charge 0.01 C is kept at rest without falling down, touching a wall by applying
an electric field 100 N/C. If the coefficient of friction between the sphere and the wall is 0.2, the
weight of the sphere is
1) 2 kg 2) 2 N 3) 20 N 4) 0.2 N
15. A charge of 1C is divided into two parts such that their charges are in the ratio of 2 : 3. These
two charges are kept at a distance 1m apart in vacuum. Then, the electric force between them in
newton is
1) 0.216 2) 0.00216 3) 0.0216 4) 2.16
16. If the force between two charged objects is to be left unchanged even though the charge on one of
the objects is halved keeping the other same, the original distance of separation ‘d’ should be
changed to
d
1) 2 d 2) d/2 3) 4) d
2
17. Two point charges q & 2q are placed at a certain distance apart. Where should a third point
charge be placed so that it is in equilibrium?
1) On the line joining the two charges to the right of 2q
2) On the line joining the two charges to the left of q
3) Between q & 2q
4) At any point on the right bisector of the line joining q & 2q
18. When 10 14 electrons are removed from a neutral metal sphere, the charge on the sphere becomes
(a) 16 C (b) 16 C
(c) 32 C (d) 32 C
q
19. Two point charges q & are situated at the origin and at the point (a,0,0) respectively. The
2
point along the X-axis where the electric field vanishes is
a 2a 2a
1) x 2) x 2a 3) x 4) x
2 2 1 2 1
20. The following figures show regular hexagons, with charges at the vertices. In which of the
following cases the electric field at the center is not zero?
1) 1 2) 2 3) 3 4) 4
21. Charges q; 2q; 3q and 4q are placed at the corners A, B, C and D of a square as shown in the
following figure. The direction of electric field at the center of the square is perpendicular to
1) AB 2) CB 3) BD 4) AC
22. A charge Q is fixed at a distance‘d’ in front of an infinite metal plate. The lines of force are
represented by
1) 2) 3) 4)
23. In the following four situations charged particles are at equal distance from the origin. Arrange
them according to the magnitude of the net electric field at origin greatest first
1) (i) > (ii) >(iii) > (iv) 2) (ii)>(i) > (iii) > (iv) 3) (i) > (iii) > (ii) > (iv) 4) (iv)>(iii
>(ii) > (i)
24. Five balls numbered (1 to 5) are suspended using separate threads. Pairs (1, 2) (2, 4) and (4, 1)
show electrostatic attraction, while pairs (2, 3), (4, 5) show repulsion. Therefore ball 1 must be
1) Neutral 2) Made of metal 3) Positively charged 4) Negatively charged
25. Charge Q is divided into two parts which are then kept some distance apart. The force between
them will be maximum if the two parts are
1) Q/2 each 2) Q/4 and 3Q/4
3) Q/3 and 2Q/3 4) e and (Q-e), where e=electronic charge
26. Five point charges each having magnitude ‘q’ are placed at the corner of hexagon as shown in the
figure. Net electric field at the centre ‘O’ is E . To get net electric field at ‘O’ be 6 E , charge
placed on the remaining sixth corner should be
1) 6q 2) -6q 3) 5q 4) -5q
27. Four charges are arranged at the corners of a square ABCD, as shown in the adjoining figure. The
force on the charge kept at the centre O is
1) zero 2) Along the diagonal AC
3) Along the diagonal BD 4) Perpendicular to side AB
28. Three charges are placed at the vertices of an equilateral triangle of side ‘a’ as shown in the figure.
The force experienced by the charge placed at the vertex A in a direction normal to BC is
1) Q 2 / (4 a 2 ) 2) Q 2 / (4 a 2 ) 3) Zero 4) Q 2 / (2 a 2 )
29. Charge Q is distributed to two different metallic spheres having radii R and 2R such that both
spheres have equal surface charge density. Then charge on the larger sphere is
1) 4Q/5 2) Q/5 3) 3Q/5 4) 5Q/4
30. The bob of a simple pendulum is hanging vertically down from a fixed identical bob by means of
a string of length ‘l’. If both bobs are charged with a charge ‘q’ each, time period of the pendulum
is (ignore the radii of the bobs)
l l l
2 2 2
q2 q2 l q2
g 2 g 2 2 g
1) l m 2) l m 3) g 4) l
