If E=MC^2, where E = energy, M=mass, C=speed of light, how can photons have energy if they are massless?
(M=zero) x C^2 = zero
2007-03-17 12:51:16 · 6 answers · asked by Raymond 2 in Science & Mathematics ➔ Physics
The full expression for the total enegy of a particle is as follows:
E = √((mc²)² + (pc)²)
where p is the momentum of the particle. If m = 0, then this becomes
E = pc
For massless particles, p = (hf)/c, where h is Planck's (reduced) constant, f is frequency, and c is the speed of light. Thus, for massless particles:
E = hf
so that the energy of light is proportional to its frequency, which is why x-rays carry more energy than infrared light, even though both are travelling at the speed of light.
2007-03-17 13:41:43 · answer #1 · answered by Scythian1950 7 · 0⤊ 1⤋
It's called 'relativistic energy' anf it's given by Planks constant times the photons frequency.
Doug
2007-03-17 20:40:32 · answer #2 · answered by doug_donaghue 7 · 0⤊ 1⤋
Because the equation means everything is energy. The faster the energy travels, the denser it gets. Even light.
2007-03-17 22:19:42 · answer #3 · answered by free_to_dream27 2 · 1⤊ 1⤋
because you use a different formula to calculate the energy of a photon,
E = hf
where f is their ferquency and h is planks constant 6.6*10^-34
and light does have a frequency.
The problem you aksed there about light having mass gave rise to guantum theory
2007-03-17 20:06:26 · answer #4 · answered by ? 2 · 3⤊ 1⤋
Check out this website, it should answer all of your questions
http://www.desy.de/user/projects/Physics/ParticleAndNuclear/photon_mass.html
2007-03-17 20:05:01 · answer #5 · answered by Tim 2 · 0⤊ 1⤋
'cuz they are always in motion and their energy is kinetic?
2007-03-17 20:06:27 · answer #6 · answered by Anonymous · 1⤊ 3⤋