Re: [Phys-l] Cerenkov radiation

[John Denker <jsd@av8n.com>]

On 07/10/2009 10:32 AM, Bill Nettles wrote:
> We were talking about the blue glow of swimming-pool reactors in
> class today and the question was raised: Where does the energy for
> the photons in Cerenkov radiation come from, the particles' kinetic
> energy, the particles' mass, the internal energy of the medium,
> elsewhere?

Kinetic energy.  It has to be, since all the other items
mentioned are constant.

It's just like any other "radiation reaction" force.  Examples
include synchrotron radiation.  No work is done on or by the
bending magnets, since they are constant.  As the particle goes
around it radiates, doing work against the EM field ... but 
meanwhile the EM field is doing work against the charge, as it 
must, to maintain energy balance. 


Quantifying the radiation reaction force is tricky.  It's the
sort of thing Feynman liked to argue with Wheeler about.