When a charged particle travels faster than the speed of light in a certain medium, then there is a release of energy in the form of "shock waves". For light, these shock waves are the Cerenkov radiation of which you ask. Perhaps it goes without saying that in a vacuum, no such radiation is possible, because n%26gt;1 for v%26gt;c.
For n=1.52, the speed of light is c (vacuum)/n (index of refraction).
V (light) in crown glass is = 1.97 E 8 m/s = .658c
We need our electron to have this velocity, and need to account for the relativistic mass...
m=m(rest)/SQRT((1-(v^2/c^2)) =
1.33m(rest) = 1.21E-30 kg
K.E. = 1/2 mv^2 = 2.36 E-14 J = 147keV (to three sig. figs.)
-Fred
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