If a newly discovered particle X moves with a speed equal to the speed of light in vacuum, then which of the following must be true?
A. The rest mass of X is zero
B. The spin of X equals the spin of a photon
C. The charge of X is carried on its surface
D. X does not spin
E. X cannot be detected
(GR8677 #68)
Solution:
Relativistic Energy: E2 = p2c2 + m02c4
If the particle moves with v = c, de Broglie relation: E = hf = pc
E2 = E2 + m02c4
m02c4 = E2 − E2 = 0
m0 = 0
Answer: A
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