If?

[Stumblebum]

I hope I'm in the right section. More questions for the astute members of this forum.

 

If a light particle(photon) has no mass then does that affect the famous equation E=mc²? or can a massless photon release energy?

 

If a photon has mass and is absorbed (lost) is there a release of energy equivalent to its mass?

 

If c=0 can there be any energy? or do things have to be in motion for the equation to work?

[Klaynos]

The equation you have quoted is for a particle at rest, as this cannot be achived with a photon you want the full form of the equation:

 

E²=(m₀c²)²+(pc)²

[CPL.Luke]

also a photons energy is E=hf or energy is equal to planks constant (h) times the frequency (f). A photon doesn't have any rest mass or m_0 . if you insist however you can apply a relativistic mass to the photon. In which case you just take the energy value from e=hf and divide it by c^2. This value is of virtually no importance though so most physicists will just use energy (in fact relativistic mass is barely used at all now for anything).

 

 

if a photon is absorbed by something it transfers its energy to that adam, usually in the form of heat but its possible to make it work for propulsion as well

 

If C was equal to 0 then there wouldn't really be any energy. However there is no accepted theory in physics (by accepted I mean like quantum mechanics accepted) that allows the speed of light to change.

[swansont]

If a photon has mass and is absorbed (lost) is there a release of energy equivalent to its mass?

 

Yes. The most striking example of this is pair production' date=' where a particle and its antiparticle are created from a photon. The minimum photon energy that can undergo pair production has an energy of 2mc[sup']2[/sup]

[ElijahJones]

Light appears to move more slowly through certain crystals. If photons have no mass how can their path be altered by gravity? Answer, its not gravity warps space and time and light is just following equivalent of a "straight" line. I'm glad someone pointed out that E=mc^2 is for a particle at rest because it explains nothing. But looking at this thread reminded me that I have never seen a good derivation of the formula or an explanation of its context. I think I'll try Wikipedia and see what they have. They claim E-mc^2 is the basis for the bomb. It must have something to do with binding energies.

[Asimov Pupil]

the two things that scrape my butt are a sander about yea high and the formula [math]E^2=(mc^2)^2+(pc)^2[/math]. how does that formula work for a particle with no mass? p is momentum right? and isn't the formula for momentum p=mv? so there is still no energy.

[5614]

Because we use the equation p=h/lambda or momentum = plank's constant divide by wavelength.