Question

Charge Q is divided into two parts which are then kept some distance apart. The force between them will be maximum if the two parts are 

(a) Q/2 each 

(b) Q/4 and 3Q/4 

(c) Q/3 and 2Q/3 

(d) e and (Q - e), where e = electronic charge

Answer 1

Correct Answer is: (a) Q/2 each 

The force of interaction = F = k q(Q - q) / d².

For F to be maximum, dF/dq = 0 = (Q - 2q) k/d²

or q = Q/2.