Question

Two charges $4q$ and $q$ are placed $30\text{cm}$ apart. At what point, the value of electric field will be zero?

• A. $10\text{cm}$ away from $q$ and between the charges.
• B. $20\text{cm}$ away from $q$ and between the charges.
• C. $15\text{cm}$ away from $q$ and between the charges.
• D. $25\text{cm}$ away from $q$ and between the charges.

Answer 1

The correct option is A $10\text{cm}$ away from $q$ and between the charges.

At equilibrium, net field at point $P$ is zero.

$E_1-E_2=0$

$\Rightarrow \frac{k\left(4q\right)}{(x\times {10}^{-2}{)}^2}=\frac{kq}{\left[\right(30-x)\times {10}^{-2}{]}^2}$

On solving this, we get, $x=20\text{cm}$

Therefore, net electric field is zero at $(30-x)\text{cm}=(30-20)\text{cm}=10\text{cm}$ away from $q$ and between the charges.