# Calculating the Magnetic Component of a Photon

I've been trying to figure this out for some time. I have found some formulae on other sites that claim to allow me to calculate the magnetic component of a photon, but I have seen so many variants of the formulae that I'm skeptical about their reliability.

I am aware that a photon is an electromagnetic wave and it consists of an electric field and a magnetic field that are perpendicular to each other. Considering that they propagate each other, it would be that at certain times, the wave would be entirely electric and at other times, it would be entirely magnetic.

Would it then be possible to calculate the magnetic field strength (B-field) of the electromagnetic wave at the point of maximum amplitude (i.e. when the wave is entirely magnetic)?

• In an electromagnetical wave in vacuum the electric and magnetic components are in phase, not out of phase. Furthermore, as coherent light waves are coherent states of photons you can extract the information (if you are only interested in mean values) from formula for classical light waves. – Sebastian Riese May 31 '15 at 16:36
• "Considering that they propagate each other, it would be that at certain times, the wave would be entirely electric and at other times, it would be entirely magnetic." You are right with your thoughts but not in accordance with the modern teaching. See the links in this answer physics.stackexchange.com/questions/152758/… – HolgerFiedler May 31 '15 at 18:05
• From what I see in the pic, it looks like the two waves are out of phase with each other. Wouldn't this mean that there would be a point where it would have a maximum magnetic field strength? – ashiswin Jun 1 '15 at 2:42

Remember that if the electric and magnetic field components are perpendicular and in phase, then you can always calculate the magnetic induction component as $|\vec{B}| = \frac{1}{v}|\vec{E}|$; where $v$ is the speed of the wave, and is given by $v = \frac{1}{\sqrt{\epsilon\mu}}$, where $\epsilon$ and $\mu$ are the relative permittivity and permeability of the medium.