Question

Point charges create equipotential lines that are circular around the charge (in the plane of the paper). What is the potential energy, in nJ, of a 1 nC charge located 0.93 m from a 2 nC charge ?

Answer 1

The potential energy of a pair of point charges is given by:

$U=k\frac{q_1q_2}{r}$

In this case we have that the distance between the charges is 0.93 m and the charges are 1 nC and 2 nC; plugging these values we have:

$\begin{gathered} U=(9\times10^9)\frac{(1\times10^{-9})(2\times10^{-9})}{(0.93)} \\ U=19.35\times10^{-9} \end{gathered}$

Therefore, the potential energy is 19.35 nJ