Focusing light

[johann]

I would like to know what happens to light as it focuses through a lens.

If the example of looking at a blue star through a telescope is taken.

 

Would it be correct to say all of the following?

The density of the photons increases

The frequency remains the same

The amplitude of the light increases

 

Thanks in advance for answering my questions

 

regards

Johann

[swansont]

Yes, that would be correct.

[dragonstar57]

the density of the individual photons would remain the same

[swansont]

the density of the individual photons would remain the same

 

?

 

The photons will be concentrated. What is "density of an individual photon" supposed to mean?

[dragonstar57]

?

 

The photons will be concentrated. What is "density of an individual photon" supposed to mean?

a photon is a particle no?

the individual particles remain the same.

just because there closer together, doesn't change the individual photons.

the overall density goes up but not the density of the individual photons.

Edited October 7, 2010 by cipher510

[darkenlighten]

I think saying the density of photons increases is misleading or just incorrect. The intensity increases, which is possibly what you guys mean. In a particle model the energy of each photon stays the same, but the amount coming in increases. In a wave model, the amplitude increases (constructive interference) and the frequency stays the same. That's the way I see it.

[Klaynos]

Photons/unit area increases. I don't think it makes much sense to talk about an individual photon having a density though... even trying to give them a tokenistic size is hard enough.

[dragonstar57]

Photons/unit area increases. I don't think it makes much sense to talk about an individual photon having a density though... even trying to give them a tokenistic size is hard enough.

but they must have density right?

even if its hard to figure out?

[swansont]

but they must have density right?

even if its hard to figure out?

 

An individual photon does not have a density. You can talk about the density of an ensemble of photons; that would be a number density.

[Cap'n Refsmmat]

but they must have density right?

even if its hard to figure out?

Density is mass per unit volume, and photons have no mass. At least in the classical sense.

[Mr Skeptic]

How about an energy density then?

[Klaynos]

http://www.scienceforums.net/topic/27337-does-a-photon-have-physical-volume-or-geometrical-size/

 

Volume is a bugger when it comes to photons...