Question

Let a total charge 2 Q be distributed in a sphere of radius R, with the charge density given by ρ(r) = kr, where r is the distance from the centre. Two charges A and B, of –Q each, are placed on diametrically opposite points, at equal distance, a from the centre. If A and B do not experience any force, then : 

(1)   a = 8^–1/4 R

(2)   a = 2^–1/4 R 

(3)   a = 3R/2^{-1/ 4} 

(4)    a = R/√3

Answer 1

Correct option (1) a = 8^–1/4 R

Explanation:

Total charge = 2 Q

Charging density ρ = kr

Radius = R