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Question:
I have understood, that a charged particle, which is accelerated, will radiate electromagnetic energy. This happens even when the speed of the particle is constant, but the direction of its movement and hence its velocity is changing. So a charge with uniform speed traveling on a circular path will radiate energy (e.g. in a cyclotron). My question is, why does an electron in an orbital around the nucleus of an atom not radiate, unless it is moving form one orbital to another? I suspect, that this has something to do with the fact, that there are only a fixed number of possible orbitals for electrons in an atom. If the electron does not radiate energy when it is in an orbital, does that mean that it is not influenced by any forces? Otherwise it would be false to state, accelerated charges always radiate energy.



Replies:
"Classical" electrodynamics predicts that an accelerating charged particle emits radiation. On the macroscopic scale, this is/was true. However, Bohr, Planck, and other scientists at the time recognized that this behavior could not apply to atoms and molecules. The only resolution was that the "classical" law did not apply to atoms and molecules. This 'ad hoc' assertion led to the Bohr model for the hydrogen atom. His assertion that electrons could only exist in certain stable orbits conflicted with the existing classical model but agreed with the experimental result. So there is an intellectual choice: Revise the theoretical model, or, ignore the experimental result. In fact there is no choice. Science is based upon what can be observed and measured, or upon adherence to the model (dogma). For science only the former is ultimately acceptable.

Vince Calder



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