Special relativity and rest mass of a photon

[Lizwi]

1) How can get work done on a photon because work done = kinetic energy it depends on mass, but the rest mass of a photon is zero
2) From this equation E=PC , does this mean E of a photon is 0 because P must be zero since it depends on mass?

 

[clamtrox]

1) How can get work done on a photon because work done = kinetic energy it depends on mass, but the rest mass of a photon is zero
2) From this equation E=PC , does this mean E of a photon is 0 because P must be zero since it depends on mass?

Remember that classical mechanics does not work for things moving at the speed of light. You need to use special relativity instead. Just because something has zero mass doesn't mean that its momentum needs to be zero.

 

[granpa]

http://en.wikipedia.org/wiki/Larmor_formula

http://en.wikipedia.org/wiki/Abraham-Lorentz_force

http://en.wikipedia.org/wiki/Abraham-Lorentz-Dirac_force#Abraham.E2.80.93Lorentz.E2.80.93Dirac_Forcehttp://en.wikipedia.org/wiki/Electr...stored_in_an_electrostatic_field_distribution

 

[Mark M]

1) How can get work done on a photon because work done = kinetic energy it depends on mass, but the rest mass of a photon is zero
2) From this equation E=PC , does this mean E of a photon is 0 because P must be zero since it depends on mass?

Hi Liziwi,

The equation for finding the energy of a photon is
$$E= \frac{\hbar c}{\lambda }$$
Where E is energy, ${\hbar }$ is Planck's constant, $c$ is the speed of light, and ${\lambda }$ is the wavelength of the light.
Also, because E=mc², an observer in relative motion with a photon will perceive it as having relative mass.

 

[ZikZak]

Also, because E=mc², an observer in relative motion with a photon will perceive it as having relative mass.

Really? What experiment does he employ to perceive this "mass" of a photon?

 

[Mentz114]

... an observer in relative motion with a photon will perceive it as having relative mass.

All observers are always in motion wrt to light with speed c. Photons are massless.