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Question: A charge \(Q\) is divided into two parts of \(q\)and\(Q - q\). If the coulomb repulsion between them...

A charge QQ is divided into two parts of qqandQ−qQ - q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of Qq\frac{Q}{q} should be

A

2

B

1/21/2

C

4

D

1/41/4

Answer

2

Explanation

Solution

Let separation between two parts be r

⇒ F=k.q(Q−q)r2F = k.q\frac{(Q - q)}{r^{2}}

For F to be maximum

dFdq=0\frac{dF}{dq} = 0 ⇒ Qq=21\frac{Q}{q} = \frac{2}{1}