Momentum of a single photon

[PaulS1950]

What is the momentum of a single photon?

Is there a way to demonstrate the momentum?

Say using a cylinder with a diameter of "D" filled with a gas of known mass/density with a height of say H=D/6.

If photons from some source, that can be measured, are directed into the cylinder with the outside of the beam of light at the tangent of the inside edge in several places along the perimeter of the cylinder will it, over time, move the gas into circulation around the cylinder?

[insane_alien]

the momentum of a photon is given by plancks constant divided by the wavelength (? been a while may be wrong on this).

 

this is tiny. really tiny.

 

but if you had a relatively powerful laser, say 100kW you could probably get some gasses moving, but really, the fact that lasers heat things up is testament to their momentum.

[Sisyphus]

The momentum of a single photon is directly proportional to its frequency. It has a magnitude equal to planck's constant divided by its wavelength.

 

If I understand the experiment correctly, then I think the gas would indeed slowly rotate.

[swansont]

Individual atoms will recoil upon absorption or emission of a photon. You can slow them down or speed them up if you shine a near-resonant laser on them.

[Airbrush]

If a photon has zero mass, then how can it have momentum? Zero times anything is zero.

Edited April 20, 2010 by Airbrush

[Icefire]

If a photon has zero mass, then how can it have momentum? Zero times anything is zero.

 

The general assumption is that a Photon has zero mass, tho more likely it's mass is difficult to detect.

[Mr Skeptic]

Zero times anything is zero.

 

Nope. Try zero times infinity.

[Cap'n Refsmmat]

Nope. Try zero times infinity.

 

Indeterminate forms don't count.

 

(Or, in other words, using infinity is cheating. )

[swansont]

If a photon has zero mass, then how can it have momentum? Zero times anything is zero.

 

p = mv is a classical notion.