Answer
$ V _r = - 6.81 \times 10^{-4} V$
Work Step by Step
We have the equation:
$ V _r = - \frac{qr^2}{8\pi \epsilon R^3} $
We know that R=r, so we simplify:
$ V _r = - \frac{q}{8\pi \epsilon R} $
We substitute the known values to obtain:
$V_r=\frac{3.5\times10^{-15}}{8\pi(8.854\times10^{-12}(2.31\times10^{-2})}$
$ V _r = - 6.81 \times 10^{-4} V$
