Question

The electrostatic force between two charges of $10\,\mu C$ and $20\,\mu C$ at a distance of $2m$ is to be halved. This can be effected by

• A. reducing both charges by 50%
• B. reducing both charges and their separation, each by 50%
• C. by doubling one of the charges and doubling the separation between them
• D. by doubling both charges as well their separation.

Answer 1

Answer: (C)

by doubling one of the charges and doubling the separation between them

Answer 2

Here, F = $k \frac{q_1q_2}{d^2}$ and F' = $k \frac{(2q_1)q_2}{(2d)^2} = \frac{1}{2}\frac{k q_1 q_2}{d^2} \, i.e.$ F' = $\frac{F}{2}$