Question

Two concentric spherical shells of radii (a) and (1.2 a) have charges (+ q) and ( -2q) respectively. At what distance from centres the numerical value of potential will be same as that of centre

A) 2.5a
B) 3a
C) 2a
D) 1.5a

Answer 1

Answer:

Superimposing the potentials (and omitting K and Q)

V = -2 / 1.2 a + 1 /a) = (-2 a + 1.2 a) / 1.2 a^2 = -.8 / (1.2 a)

Vi = -1 / (1.5 a)    at the center of the spheres

Outside the spheres

Vo =  -1 / R  since the net charge is -Q

Thus R = 1.5 a