Frank-Tamm formula
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The Frank-Tamm formula yields the amount of Cherenkov radiation emitted as a charge particle moves through a medium at superluminal velocity.
When a charged particle moves faster than the speed of light in a medium, it can emit a photon while conservating energy and momentum, this process can be viewed as a decay.
[edit] Equation
The Energy emitted per unit length (travelled by the particle) per unit frequency is:
,
where μ and n(ω) are the permeability and index of refraction of the medium, q is the electric charge of the particle, v is the speed of the particle, c is the speed of light in vacuum, and ω is the angular frequency of radiation.
The total amounted of energy radiated per unit length is:
This integral is done over the frequencies which the particle's speed v is greater than speed of light of the media 
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