physbod

Well, yes, but doesn't the frequency of the EM wave determine the energy of each photon (E=hf)? So when the power decreases, what are we talking about here....fewer photons per second? I think the original query was talking about how, if at all, the physical amplitude/extent of the electric and magnetic field changes, if at all, and how can it be measured, if at all? I just can't visualise this and would really like to know!