50. The force between two charges separated by a distance d in air is 10 N. When the charges are placed same distance apart in a medium of dielectric constant Cr, the force between them is 2 N. What is the value of Cr?

A.0.5

B.20

C.5

D. none of above

51. Two small spheres, each carrying a charge Q, placed d metres apart repel each other with a force F. If one of the spheres is taken around the other one in a circular path of radius r, the work done will be

A. zero

B. F x

C.Fxr

D. F/27c

52. Two charges +3 AC and -12 AC are separated by a distance of 0.4 m. Where should a third charge of +3 AC be placed from +3 AC so that it experiences zero force?

A. 0.4 m

B. 0.2 m

C. 0.3 m

D. 0.1 m

53. For a dipole electric field varies as

A.2

B.73

C.71

D. T-4

54. When a charge is brought from infinity along the perpendicular bisector of a dipole, the work done is

A. positive

B. negative

C. zero

D. none of above

55. An a-particle is accelerated through a potential difference of 104 V. The gain in kinetic energy of the a-particle is

A. 2 x 10-4 eV

B.2 x 104J

C. 2 x 104 eV

D. none of above The electric potential at a point in air

56. due to a point charge is 9 V. If air is replaced by a medium of relative permittivity 3, then electric potential at that point will be

A. 27 V

B. 3 V

C. 18 V

D. 36 V

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