And here they consider that there is no moment of momentum. https://susy.page/2015/09/20/hidden_momentum It can be translate by google-translate. I really don’t understand anything about Poynting vectors, but please tell me that https://susy.page/2015/09/20/hidden_momentum is mistaking.
The Poynting vector, the vector multiplication of E and H, represents EM power flow with the dimensions of watts/square meter. As a power flow there must be a source and that defines something about the E and H, they must both come from the same source. It is possible to have E and H from different sources, in which case the E X H product is not a real Poynting vector, it is a pseudo vector with no real meaning. When we do have a real Poynting vector, from relativity theory the equivalence of mass and energy means the energy flow has a (hidden) momentum. The pseudo vector does not have hidden momentum since it does not represent energy flow. The article you refer to with radial E field and circular H field has the pseudo vector so it did not need the long winded to approach to reach its (correct) conclusion, it is obvious right from the start. (There is a real Poynting vector with radial E field and circular H field within a coaxial cable, and that meets the requirement that E and H come from the same source.) My point about hidden momentum is not the Poynting vector, but the consideration that charge Q in a vector magnetic potential A has a (hidden) momentum Q* A. Because in any pratical experiment the forces are so small it may need a superconducting conductor to be used to obtain observable results. Smudge
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