Name: Eric D.
Accelerating free electrons radiate electromagnetic waves. A free electron undergoing uniform circular motion is accelerating, but its speed is constant. Does it radiate electromagnetic waves?
Yes. This is how synchrotrons make x rays. The energy radiated decreases the electron's speed.
Accelerating electron has momentum, whether it is linear momentum in the case of linear motion or angular momentum in the case of orbital motion. It radiates electromagnetic waves in both cases. However, that does not apply to electrons at the atomic level. Bohr made the ad hoc assumption that an electron in a hydrogen atom did not radiate energy and spiral into the nucleus. At the time this was revolutionary to say the least, but it was necessary to explain the spectrum of the hydrogen atom.
Yes. it certainly does. Centripetal acceleration is just as real as
acceleration which changes speed as you can check the next time you take a
ride in your car.
In fact, this is a problem when accelerating electrons to very high energies
and is the reason for linear accelerators such as the two mile long linear
accelerator at the Stanford Linear Accelerator Center (SLAC) near Stanford
University. There is also radiation as the electrons are accelerated in a
straight line, but much less than in a standard circular accelerator where
the particles go around many times while being accelerated
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
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Update: June 2012