Introduction to Electrodynamics · Problem 8.19

Electromagnetic Waves — David J. Griffiths

Physics · electromagnetic-angular-momentum

Problem

Suppose you had an electric charge

q_e

and a magnetic monopole

q_m

. The field of the electric charge is

\mathbf{E} = \frac{1}{4\pi\epsilon_0}\frac{q_e}{r^2}\hat{r}

(of course), and the field of the magnetic monopole is

\mathbf{B} = \frac{\mu_0}{4\pi}\frac{q_m}{r^2}\hat{r}.

Find the total angular momentum stored in the fields, if the two charges are separated by a distance

d

. [Answer:

(\mu_0/4\pi)q_e q_m