# What is Cherenkov radiation? [duplicate]

What is Cherenkov radiation? I came across this concept when I was learning SR. Why can't particles moving at speed of excess of speed of light in the medium. Why it does not violate the limitation is speed?

• Have a look at How can a particle in a medium ever travel faster than light? and see if it answers your question. If not, prehaps you could edit your question to be more specific about what you are asking. – John Rennie Feb 10 '19 at 6:08
• @JohnRennie please upvote the question so that i can enter the chat rooms (I know these types of comments are accepted but what to do I want to get into h bhar):/ – user221098 Feb 10 '19 at 7:28
• It is the sonic boom equivalent (airplanes going faster thant he speed of sound in the air.) hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel.html – anna v Feb 10 '19 at 14:40

In certain phases of nuclear research and technology, a luminous glow may be observed where high- energy particles are moving through transparent matter. This is known as Cherenkov radiation, and is the result of particles moving through matter at speed in excess of the speed of light in that medium. This does not constitute a violation of limitation is the speed of physical bodies to values less than $$c$$ for in relativity the speed is light always and invariably means its speed in a vacuum. Since the index of refraction of water is about $$\frac{3}{4}$$, light travels at about $$2.25 \times10^8 \,\rm m\,s^{-1}$$ in water and Cherenkov radiation would be produced by particles having a velocity greater than this value. However, all such speeds would be less than $$c$$ which is not $$2.25\times 10^8 \,\rm m\,s^{-1}$$ but $$3.00\times 10^8\,\rm m\,s^{-1}$$.