Question

Two charges of magnitude $5\, nC$ and $-2\, nC$, one placed at points $(2\, cm, 0,\, 0)$ and $(x \,cm, 0, 0)$ 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. $20\, cm$
• B. $80\, cm$
• C. $4\, cm$
• D. $16\, cm$

Answer 1

Answer: (A)

$20\, cm$

Answer 2

Potential energy of system $U=\frac{1}{4\pi\varepsilon_{0}} \frac{q_{1}q_{2}}{r}$ $0.5\times10^{-6}=\frac{9\times10^{9}\times5\times10^{-9}\times\left(-2\right)\times10^{-9}}{\left(x-2\right)\times10^{-2}}$ $\Rightarrow x=20 \, cm$