What is the mass of a photon if e=MC(2)?

Question

OK, so, if E=MC squared (and I am sure it does!), then I have never understood how a photon can be massless if it has energy?

Answer 1

Photons do not have mass but we sometimes talk about their "effective mass" when discussing problems such as scattering problems. Photons do have momentum so sometimes it is easier to think of them as a point mass to work out scattering angles etc.

The energy of a photon is hv where h is plank's constant and v is the frequency, and its effective mass is, from E= M*C^2, equal to hv / c^2.

The equation E=M*C^2 descibes how mass and energy can be interchanged. The photon has energy that can be converted into mass, but that does not mean it has mass. Think of it like a currency exchange ratio; you can change $100 into euro, but that does not mean you had any euro to begin with.

Answer 2

Photons are massless but carry energy and momentum.

The equation to work out the energy a photon carries is-:

Energy = Planck Constant * Frequency

i.e. the greater the frequency the more energy it has.

Answer 3

Photons have wave-partical duality, so depending on the situatuion, they can me massless, or not. Another way of getting around problems by us phyicists :oD

Answer 4

This question usually comes up in the context of wondering whether photons are really "massless," since, after all, they have nonzero energy. The problem is simply that people are using two different definitions of mass. The overwhelming consensus among physicists today is to say that photons are massless. However, it is possible to assign a "relativistic mass" to a photon which depends upon its wavelength.

From my own understanind.. mass and energy are just relative at high speeds energy can become mass.  Hence why it would be impossible to go faster than the speed of light... you would just get heavier and heavier the more enegry you out in... according to Einstein that is.