Understanding the Paradox of Photon Momentum: Electromagnetic Force Revealed

[scilover89]

Momentum can be categorised under electromagnet force, and electromagnetic force carrier is photon. But photon have momentum. Isn't this paradoxical?

 

[Antiphon]

The classical electromagnetic field has momentum. The photon is the
quanum mechanical minimum unit of this field, and it also carries this
momentum.

There is no paradox.

 

[Sterj]

Mhh, how can it carry momentum if it has mass of zero? Momentum is p=m*v. Or is here the meaning of the quantum mechanical operator?

 

[Antiphon]

According to E=mc^2, energy and mass are eqivalent in this case.

Moving energy must carry momentum. It does not require the
presence of a classical mass.

A compressed spring is a little heavier than a loose one. If they move at
the same speed, the compressed one has more momentum.

 

[jtbell]

Mhh, how can it carry momentum if it has mass of zero? Momentum is p=m*v.

No, in relativity theory it's possible for a particle to have momentum and energy even though it has zero mass. The general relationship between mass, energy and momentum is

E^2 = (pc)^2 + (mc^2)^2

Set m = 0 and you have E = pc which in fact has been verified for electromagnetic radiation.

 

[Sterj]

So for photons this equation can be written as:
E^2=(pc)^2

 

[Antiphon]

So for photons this equation can be written as:
E^2=(pc)^2

Yes. E=hf, p=f/h where h is Planck's constant, when you are talking about
photons. For classical fields, momentum/m^2=ExH/c^2, energy/m^2=ExH.

 

[Strafespar]

Yeah, you are thinking in terms of classical physics.

 

[ansgar]

Yeah, you are thinking in terms of classical physics.

5 year old thread