Question

Two small diameter 10gm dielectric balls can slide freely on a vertical channel. Each carry a negative charge of 1μC. Find the separation between the balls if the lower ball is restrained from moving.

(a) 0.5

(b) 0.4

(c) 0.3

(d) 0.2

I have been asked this question in unit test.

My question comes from Coulomb Law in division Electrostatic Fields of Electromagnetic Theory

Answer 1

Correct answer is (c) 0.3

Best explanation: F = mg = 10 X 10^-3 X 9.81 = 9.81 X 10^-2 N.

On calculating r by substituting charges, we get r = 0.3m.