Classical Physics


Spin Tensor of Electromagnetic Waves

Authors: Radi I. Khrapko

In the frame of the standard electrodynamics, a torque is calculated, which acts from a circularly polarized electromagnetic beam with a plane phase front on an absorbing surface. And a moment of momentum flux in the same beam is calculated in the frame of the same electrodynamics. It is found that this torque is twice more than the moment of momentum flux. We have inferred that the calculation of the electromagnetic angular momentum flux in the beam is incorrect. Namely, this calculation takes only a moment of momentum into account as an angular momentum, and does not take account of spin. An analysis of the field theory foundations of the electrodynamics confirms this inference. Some changes in the field theory allow obtaining an electrodynamics' spin tensor, which accompanies the Maxwell energy-momentum tensor. Using this spin tensor for the beam yields the equality between the torque and the angular momentum flux. In this way, the electrodynamics is completed by a spin tensor. A criticism of an AOP reviewer and my answer are presented.

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[v1] 1 Oct 2008

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