1. Apr 12, 2012

### blokeice

If you get an electron going faster than the local speed of light i know that it starts emitting light, but why does it do this?, furthermore, In a theoretical material with an infinite index of defraction (a.k.a light is stopped within it), wouldn't that cause the system to quickly go to near absolute zero?

2. Apr 12, 2012

3. Apr 12, 2012

### Bob S

The best derivation of Cerenkov radiation by a fast charged particle I have seen is the semi-classical derivation in Schilff Quantum Mechanics (2nd Edition) pages 267-271. Schiff derives the classical E and H fields, and the resulting Poynting vector P = E X H. He then gets the number of quanta radiated per unit path length in frequency interval ω to ω+dω:
$$dN=\frac{1}{137}\left(1-\frac{c^2}{n^2v^2} \right)\frac{d\omega}{c} \text{ photons per unit length}$$ which becomes for infinite index of refraction
$$dN=\frac{1}{137}\frac{d\omega}{c} \text{ photons per unit length}$$
So the total number of quanta depends on wnat interval the frequency interval dω covers. Normally, the index of refraction is n ≤1 for wavelengths less than ~ 1000 Angstroms (UV).