Question

A charge Q is divided into two parts of q and Q – q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of Q/q should be ______.

Options

• 2 : 1

• 1/2

• 4 : 1

• 1/4

Answer 1

A charge Q is divided into two parts of q and Q – q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of Q/q should be 2 : 1.

Explanation:

Let separation between two parts be r, then

F = `("k"."q"("Q"-"q"))/"r"`,
For F to be maximum `"dF"/"dq"` = 0 then `"Q"/"q" = 2/1` = 2 : 1