Oscillating Charge: How Does it Create Electromagnetic Radiation?

[shamsheerc]

Hi,

In high school physics we are taught that when a charge oscillates it results in electromagnetic radiation. Then we are taught that electromagnetic radiation is a wave with the electric field oscillating in one plane and the magnetic field oscillating in a plane perpendicular to it. So if hypothetically I have a minute charged particle and it is in simple harmonic motion, then does one oscillation create one wave (one photon?)? Or is it a continuous oscillation that creates a wave? How does this work?

Could someone please clarify this and introduce me to concepts that will further help me understand how vibrating charges create radiation?


Thanks,
Shamsheer

 

[vanhees71]

An oscillating charge does not create one photon. In fact it is pretty difficult to produce really one single photon. Nowadays this can be done very effectively with non-linear crystals using the so-called parametric down conversion. There you fire with a laser into a crystal, which (sometimes) produces a pair of photons, which are "entangled". Then, triggering to those events by measuring one of these photons, one has for sure one single photon to do experiments with.

What you get by an oscillating charge, e.g., a current in a simple dipole antenna are classical electromagnetic waves. Quantum mechanically those are socalled coherent states, for which the photon number is not a fixed quantity, but it's a superposition of a lot of photon-number states (including the vacuum, i.e., the zero-photon state). The photon number in such a states is distributed according to a Poisson distribution.

 

[shamsheerc]

Thanks for the reply. I guess I need more theory about quantum physics to understand this better.