Question

Calculate the amount of work done required in moving $5\times {10}^{20}$ electrons across two points of a wire with a potential difference of $8V$.

Answer 1

Given:
Potential difference, $V=8V$
No. of electrons, $n=5\times {10}^{20}$
Magnitude of charge on an electron, $e=1.6\times {10}^{-19}C$

So total charge that has to be moved is:
$Q=ne$
$Q=5\times {10}^{20}\times 1.6\times {10}^{-19}C$
$Q=80C$

Work done in moving this amount of charge,
$W=VQ$
$W=8V\times 80C$
$W=640J$