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A certain charge Q is divided into two parts q and (Q − q). How should the charges Q and q be divided so that (Q − q) placed at a certain distance apart experience maximum electrostatic repulsion ?

1. Q = q/2
2. Q = 2q
3. Q = 4q
4. Q = 3q

Correct answer: Q = 2q

Solution

To achieve maximum electrostatic repulsion between the two charges, the force between them, which is proportional to the product of the charges, should be maximized. The optimal division occurs when one charge is twice the other, leading to the relationship Q = 2q, which maximizes the product Q(Q - q) at a fixed total charge.

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