What is meant by electromagnetic angular momentum? Can an electric field alone (magnetic field = 0) have any kind of momentum?

Question

Needed to understand this. Was studying classical mechanics from Goldstein when this popped up. It stated: "... in an isolated system of moving charges it [some generalisation of P or L ] is the sum of the mechanical angular momentum and electromagnetic "angular momentum" of the field that is conserved."

Thank you

Answer 1

Q1. In the standard theory the total angular momentum of the field is ${\bf r} \times {\bf P} $, where $\bf P$ is the Poynting vector. Note that this depends on whatever origin of the coordinate system you choose.

Q2. No, as the Poynting vector vanishes in this case.