Electromagnetic radiation is emitted when a charged particle moves through a med

Question

Electromagnetic radiation is emitted when a charged particle moves through a medium faster than the local speed of light. This radiation is known as Cerenkov radiation. Cerenkov radiation is found in many interesting places such as particle detectors and nuclear reactors and can even be seen by astronauts when cosmic rays traverse their eyes. It should be stressed that the particle is never going faster than the speed of light in vacuum (or c) Just faster than the speed of light in the material (which is always less than c). The creation of Cerenkov radiation occurs in much the same way that a sonic boom is created when a plane is moving faster than the speed of sound in the air. The various wavefronts that propagate in the material add coherently to create an effective shock wave. In this problem, you will become familiar with this type of radiation and learn how to use its properties to get information about the particles that created it. What is the threshold velocity v_threshold (water) (i.e.. the minimum velocity) for creating Cerenkov light from a charged particle as it travels through water (which has an index of refraction of n = 1.33)? Express your answer as a multiple of c to three significant figures. What is the threshold velocity v_threshold (ethanol) for creating Cerenkov light from a charged particle as it travels through ethanol (which has an index of refraction of n = 1.36)? Express your answer as a multiple of c to three significant figures. Which of the following best explains why neutrally charged particles can't give off Cerenkov radiation?

Explanation / Answer

(a) threshold velocity is just (1/n) c so . (1/1.33) c = 0.752 c . (b) (1/1.36) c = 0.735 c . (c) Neutral particles don't interact with theelectromagnetic fields of the medium.

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