Research On The Electromagnetic Angular Momentum

Electromagnetic momentum and angular momentum are interesting and basic topics of classical electromagnetism.For static electromagnetic field,there are four kinds of equivalent methods to calculate the momentum.But for the angular momentum,the situation is much more complicated,we discussed about it.In addition,we analyzed the total angular momentum of a simple electromagnetic system from establishing it to stability and then removing the field in this work.We concluded that in the process of establishing a static electromagnetic field,part of the impulse moment provided by the external force is converted into the electromagnetic angular momentum which is stored in the field,and part of it is converted into the rotating mechanical angular momentum of the system.When the field is removed,the electromagnetic angular momentum converts into the mechanical angular momentum,and the total angular momentum of the system is conserved.In the unsteady electromagnetic field,electromagnetic angular momentum can be decomposed into electromagnetic spin angular momentum and orbital angular momentum.spin angular momentum is associated with polarization,and the orbit angular momentum is associated with helical phase fronts.Scientists provide a new set of conservation laws,helicity,spin angular momentum,Nij are the associated conservation quantities.they have the similar properties with electromagnetic energy,momentum,and stresses,helicity is conserved,transferred by the spin angular momentum,spin angular momentum is also conserved,transferred by the Nij,and Nij are conserved,transferred by the Nijk.