If the photon (as a quantum of the electromagnetic field) has no defined(?) amplitude, how does (or where from?) the electromagnetic wave's amplitude appear?
The formulation of the question is not quite precise, but the main idea is if we cannot define the single photon's amplitude, since $E=hf$ only (are there any other equations?), how can we talk about an amplitude of an EM wave, which is carried via photons (EM quanta)?
