1. H

    Proca Equations and nonzero mass of photon

    Hi. I'm a 3rd year undergraduate and have to do a 15 page assignment about Proca equations and how those lead to an effective mass of photon that isn't zero. I don't even know where to begin. Can anyone recommend me something about this issue?
  2. E

    Non-zero divergence

    Hello! I was wondering if there is any configuration of ordinary magnets that can produce a field for which the divergence is non zero? and how would this configuration look like?