This is probably extremely basic physics that I don't know, but I'm still going to ask:

Say in hydrogen, according to the Bohr model the electron is "really" orbiting the proton, and as a consequence would have to continuously emit radiation thus losing kinetic energy and should then fall towards the proton. So this is obviously not correct, except that I don't know/understand why it's circular motion necessarily mean it has to emit radiation... ?


From Maxwells equations we know that accelerated charged particles emit em waves.

This can be seen from the electromagnetic wave equation, where a second derivative of the electric field is involved. If the second time derivative of the charge density is nonzero, also the second time derivative of the electric field is non vanishing and electromagnetic waves are formed. A circular motion is a accelerated motion (towards the center of the circle) and therefore it should emit em waves.

Note that in Bohr's model the fact that electrons on quantized trajectories do not emit radiation is an postulate.

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  • $\begingroup$ I actually knew this and forgot. As for now I knew the answer is Maxwell, but I didn't see it by looking at the equations. Easier to ask here than to derive from his equations myself, although I might have worked it out who knows... :-P Thank you. $\endgroup$ – user76568 Oct 9 '14 at 15:18
  • $\begingroup$ I have to admit that Bohr's postulate makes a lot of sense... $\endgroup$ – user76568 Oct 9 '14 at 15:24
  • $\begingroup$ It does? For me it always sound like " I don't know why so i postulate it", but maybe I am wrong... $\endgroup$ – Noldig Oct 9 '14 at 20:54

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