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?
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
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?
54. When a charge is brought from infinity along the perpendicular bisector of a dipole, the work done is
55. An a-particle is accelerated through a potential difference of 104 V. The gain in kinetic energy of the a-particle is
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
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