Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: CZARCAR on 27/11/2011 13:15:15

Title: ?e=mc2 & massless photons?
Post by: CZARCAR on 27/11/2011 13:15:15
i dont get it. if mass=0, then photon has no energy?
Title: ?e=mc2 & massless photons?
Post by: JP 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.
Title: ?e=mc2 & massless photons?
Post by: CZARCAR on 27/11/2011 17:20:22
thanx