Cherenkov radiation Why the EM waves are constructive

[HARI A]

I was reading an article about Cherenkov radiation in wikipedia. If the electron moves slower than light the EM waves in the medium are destructive and if they travel faster than light waves are constructive .Why so?When the electron travels faster than light the radiations cannot interfere since they have equal direction and speed.(I think so).Please give me an explanation.

 

[Pseudo Epsilon]

id like to that as well.

 

[jtbell]

It might be instructive to study the analogous situation of a "sonic boom" produced by an airplane moving faster than the speed of sound. Note the diagrams (especially the one labeled "Mach cone angle") and animation:

https://en.wikipedia.org/wiki/Sonic_boom