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Q & A: Does a photon have momentum?

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Most recent answer: 09/10/2012
Q:
photon have zero rest mass how can it possiable its momemtum
- pintukumaryadav (age 18)
purnia bihar india
A:
Yes it does.  Although the photon has zero rest mass, it does have energy.   From the relativistic relationships among Energy, Mass, and Momentum,    E2 = (Moc2)2  +  (pc)2,  if the rest mass is zero then the momentum is give by p = E/c.  Consider a photon bouncing directly back from a small mirror.   It is observed by direct experimental measurement that if a laser beam is reflected from a mirror, the mirror will recoil with the same amount of momentum that the photon had (minus a tiny amount do the slight wavelength shift in the recoiling photon).
Even in classical electromagnetic theory a traveling wave caries energy and momentum in the same ratio.

LeeH

(published on 09/10/2012)

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