# Radiation of an accelerating charge

1. Aug 3, 2014

### HAMJOOP

Suppose a point charge is accelerating uniformly. It emits EM radiation.

If an observer is co-moving with the point charge, the point charge remains at rest in his/her frame.
So I guess it does not radiate relative to the co-moving frame.

But someone told me that acceleration is absolute (something like that), and therefore the charge iis still radiating in the co-moving frame. So which one is correct ?

2. Aug 3, 2014

Staff Emeritus
It radiates. And one can tell one is in an accelerating frame because one feels a force.

3. Aug 5, 2014

### Jano L.

This is a confusing topic, because there is no generally agreed meaning to the word "EM radiation" with respect to non-inertial frame of reference. EM field and EM radiation are in practice always talked about in the context of inertial frame, because there they are quite well understood with Maxwell's equations and the Lorentz force formula.

The formula that gives the component of EM field we call EM radiation (the part falling off as $1/r$) says the field in an inertial frame is the higher the higher the acceleration of the charged particle in that same frame. There is no such formula generally known for non-inertial frames. It surely can be derived and perhaps has already been published in some obscure paper of textbook, but it is not generally acknowledged. This is partly because description in non-inertial frames is difficult, and partly because the focus has traditionally been on description in inertial frame, which is quite successful and often sufficient. For example, it is sufficient to describe radiation of an antenna or of the Sun in the frame of the Earth, because that is where we live. Corresponding description of EM field in the frame of some oscillating electron does not seem too useful.

But it is interesting project to do so anyway. As soon as we jump into accelerated frame of reference, everything changes. Maxwell's equations are not longer valid, non-electromagnetic forces appear etc. One way to find out how things are to be described and talked about in non-inertial frame is to calculate everything in inertial frame and use transformation between the two frames. This is complicated and demanding task. I do not think there has been much success in understanding electromagnetic theory in non-inertial frames, but I could be wrong.

4. Aug 5, 2014

### vanhees71

In the current issue of Am. J. Physics there's a paper by Griffiths et al on the em. field of the uniformly accelerating point particle. It's highly non trivial, as is worked out there in detail.

5. Aug 5, 2014

### WannabeNewton

Do you happen to have a link to the paper? Thanks.

6. Aug 6, 2014