Title: Optical Angular Momentum in Classical Electrodynamics,
Abstract: Invoking Maxwell's classical equations in conjunction with expressions for
the electromagnetic (EM) energy, momentum, force, and torque, we use a few
simple examples to demonstrate the nature of the EM angular momentum. The
energy and the angular momentum of an EM field will be shown to have an
intimate relationship; a source radiating EM angular momentum will, of
necessity, pick up an equal but opposite amount of mechanical angular momentum;
and the spin and orbital angular momenta of the EM field, when absorbed by a
small particle, will be seen to elicit different responses from the particle.