# Do frame dependent charges radiate?

1. May 10, 2014

### jartsa

Let's say there's an electric current in a neutral loop of wire. Then we change to a frame where the loop is moving. That makes the loop an electric dipole, for us.

Then somebody shakes one side of the loop, the positive side for example.

Do we observe EM-waves?

Here's a picture of the loop moving to the right:
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Last edited: May 10, 2014
2. May 10, 2014

### UltrafastPED

While the loop is being shaken it is not in any inertial reference frame.

And yes, it will radiate EM waves, but it is much more effective to modify the current than to shake the loop.

3. May 10, 2014

### ghwellsjr

Why not? He specifically said, "we change to a frame where the loop is moving". Would you say the loop is in the inertial reference frame in which it is moving but then when someone shakes one side of the loop it some how exits that and all other inertial reference frames? This doesn't make any sense to me. Please elaborate.

4. May 10, 2014

### UltrafastPED

... and then somebody shakes it. Shaking requires a force; if it feels a force it is not in an inertial reference frame.

5. May 10, 2014

### DrGreg

I think ghwellsjr is objecting to the phrase "not in any inertial reference frame" when you really mean "not at rest relative to any inertial reference frame".

6. May 10, 2014

### ghwellsjr

Before somebody shakes it, is it in the inertial reference frame in which the OP said it is moving?

7. May 10, 2014

### vanhees71

I think it's a bit misleading to say "something is in a inertial or non-inertial reference frame". The question is whether you describe a situation within an inertial or a non-inertial reference frame or to put it more physically whether the observer is in an inertial frame ("inertial observer") or accelerated relative to the class of inertial frames ("accelerated observer").

As described by the OP the circuit is always considered to be observed from an "inertial observer". I'd keep it in the reference frame, where it is initially at rest and then shaken. Of course, when it is shaken it will radiate em. waves. This is so because you have effectively accelerated charge distributions even if the wire is overall neutral due to relativistic effects of currents and charges.