Question

Determine the electrostatic potential energy of a system consisting of two charges $7\mu C$ and $-2\mu C$ (and with no external field) placed at $(-9cm.0.0)$ and $(9cm,0.0)$ respectively.

Answer 1

$\text{Step 1: Potential energy of system}$

For a system of two charges $q_1$ and $q_2$ separated at a distance $r$, Potential Energy is given by:

$U=\frac{1}{4\pi {\epsilon }_0}\times \frac{q_1{q}_2}{r}$

$\text{Step 2: Solving equation}$

From Figure, $r=18cm=0.18m$

$U=9\times {10}^9\times \frac{(7\times {10}^{-6}C)\times (-2\times {10}^{-6}C)}{0.18m}$

$\Rightarrow U=-0.7J$

Negative sign indicate that the interaction between the charges is attractive.

Hence, the potential energy of system is $-0.7J$