Question

Two charges of magnitude $5nC$ and $-2nC$, one placed at points $(2cm,0,0)$ and $(xcm,0,0)$ in a region of space, where there is no other external field. If the electrostatic potential energy of the system is $-0.5\mu J$. The value of $x$ is :

• A. $20cm$
• B. $80cm$
• C. $4cm$
• D. $16cm$

Answer 1

The correct option is A $20cm$

Potential energy of system
$U=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r}$
$0.5\times {10}^{-6}=\frac{9\times {10}^9\times 5\times {10}^{-9}\times (-2)\times {10}^{-9}}{(x-2)\times {10}^{-2}}\Rightarrow x=20cm$
$\Rightarrow$ $x=20cm$