Question

A charge of 4 µC is to be divided into two. The distance between the two divided charges is constant. The magnitude of the divided charges so that the force between them is maximum, will be: 

Options

• 1 µC and 3 µC

• 2 µC and 2 µC

• 0 and 4 µC

• 1.5 µC and 2.5 µC

Answer 1

2 µC and 2 µC

Explanation:

Let r be the separation between the two divided charges.

the force between two charges according to Coulomb's law,

F = `("Kq"(4 -"q"))/"r"^2`

For F to be maximum

`"dF"/"dq"= "K"/"r"^2[4-2"q"] = 0`

⇒ q = 2