# Angular momentum and EM wave

Is there any sense in saying that circularly polarized EM waves have angular momentum?

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Yes. Electromagnetic waves carry energy and momentum, and can carry angular momentum.

A linearly polarized wave packet doesn't carry any angular momentum (measured about an axis through its center -- a linearly polarized wave packet moving past you off to one side has angular momentum about an axis located where you are, just as a baseball flying past you does.)

A circularly polarized wave packet does carry angular momentum about its center ("spin" as opposed to "orbital" angular momentum, roughly).

Hi @Igor, the best way to count the angular momentum is in terms of photons. A photon carries the energy $E=hf=\hbar \omega$ and if it is circularly polarized, the angular momentum in the direction of motion (around this axis) is $\pm\hbar =\pm h/2\pi$. So the ratio of energy and angular momentum of the photon - and the same for a big electromagnetic wave - is $\omega=2\pi f$. – Luboš Motl Mar 11 '11 at 19:32