Question

A +40 μC point charge is placed 32 cm from an identical +40 μC charge. How much work would be required for an external force to move a +0.70 μC test charge from a point midway between them to a point 13 cm closer to either of the charges?

Answer 1

Electric potential due to point charge is given by

V=KQ/r

Work done  for an external force to move a +0.70 μC test charge is

$W=q\left ( V_{2}-V_{1} \right )$

$W=(0.7\times 10^{-6})(9\times 10^{9})(40\times 10^{-6})\left ( \left [ \frac{1}{(0.16-0.13)}+\frac{1}{0.16+0.13} \right ]-\left [ \frac{1}{0.16}+\frac{1}{0.16} \right ] \right )$

W=6.12 Joules