?e=mc2 & massless photons?

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Offline CZARCAR

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?e=mc2 & massless photons?
« on: 27/11/2011 13:15:15 »
i dont get it. if mass=0, then photon has no energy?

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Offline JP

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?e=mc2 & massless photons?
« Reply #1 on: 27/11/2011 13:29:23 »
That's only the correct equation when you're calculating the energy of something that is sitting still.  Light always moves at light speed, so the correct equation in that case is:

E2=(mc2)2+(pc)2,

where p is momentum.  A photon has no mass (m=0), but it has momentum, (p≠0).  Therefore, it has energy.

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Offline CZARCAR

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?e=mc2 & massless photons?
« Reply #2 on: 27/11/2011 17:20:22 »
thanx