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Q & A: Momentum and energy of photons (and other particles)

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Most recent answer: 05/28/2010
Q:
If a photon has zero rest mass, then how it could have energy in terms of E=MC^2 (M is rest mass). If M is zero then E is also zero. Isn't it this way?
- Indrajit
New Delhi, India
A:
You wrote down only part of the full equation.  The correct relation between energy, mass and momentum is  E2 = (mc2)2 + (pc)2, where p is the momentum.   So for a zero rest-mass photon it becomes E =  pc.
No problem. 
Look at   for more information.

LeeH

(published on 05/28/2010)

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