Electromagnetic Waves – Relationship with Photons

Question

An EM wave consists of photons. How are they generated?

It’s my understanding that a radio transceiver creates an oscillating voltage on a conductor matched with a ground; this device being an antenna. Do charged electrons move back and forth at high energy from the conductor to ground? In this process perhaps collide with each other, moving an electron to a higher energy orbital state, then lower state which causes a photon emission at some angle?

Answer 1

A radio wave is a special form of EM radiation.

In a thermal source, excited electrons "collide with each other, causing an electron to go to a higher energy state and then to a lower energy state, causing photon emission." That's right.

The same thing happens in the antenna rod. The differences with a thermal source are

• the electrons are accelerated synchronously in the same direction, which produces polarized radiation
• the oscillating intensity of the emitted photons depends on the power of the wave generator and the matching of the intended frequency with the length of the antenna rod
• each individual photon moves only a bit along the rod (see drift velocity) and collides many times with other electrons.

The consequence of your question is that a radio wave is an oscillating stream of photons with very different frequencies.