Homework Help: Particle model of light

1. Apr 3, 2009

pillanoid

1. The problem statement, all variables and given/known data

If the two slits in a two-slit interference experiment were so far apart that their diffraction patterns did not overlap, would the pattern displayed be consistent with a particle model of light?

2. Relevant equations

3. The attempt at a solution

I said that it would not, since there would be diffraction of each individual slit's pattern (meaning each would look like a bunch of concentric circles).
My professor said that it would be consistent with the particle model of light, but I couldn't really understand his explanation.
It's my understanding that in the particle model of light, the light from each slit would then just be a concentrated thing of light without diffraction, so I may be wrong there, but either way, can someone please explain this?

2. Apr 3, 2009

turin

No. The essence of the particle nature of light is manifested in interactions, i.e. hitting the screen.1 The motion of a photon, including passage through a slit, is governed by the wave equation (Maxwell's equations).

1 Particle behavior also modifies the vacuum, but since this is in the intro phys forum, that is probably too advanced to discuss here.

3. Apr 4, 2009

pillanoid

Oh, okay. So in the particle model of light, each photon will act as a particle, and the path it takes is determined by the wave equation (which I'm guessing involves some uncertainty principle or something like that?). The resulting diffraction (the concentric circle pattern) is due to the fact that there are so many photons, and each follows its own path. Or at least would be the case if the particle model were true. Is that what you meant?

4. Apr 4, 2009

turin

Not exactly. The manifestation of wave or particle behavior is determined by circumstance. EM radiation containing a single photon's worth of energy still obeys Maxwell's equations, and it has no definite photon composition. This radiation collapses to a photon at the moment when it hits the screen.

5. Apr 4, 2009

pillanoid

Is that the particle model or what "actually" happens?

6. Apr 5, 2009

turin

Hmm. Interesting point. I would say that the term "model" should not really be used here. Alternatively, I would say that light can be modelled as particles, but then it will be difficult to describe many optical phenomena, e.g. diffraction. I would say that light does not have particle and wave models, but rather particle and wave descriptions, and the appropriate description depends on circumstance. For unobstructed light in a vacuum, either description is just as appropriate. When you start complicating the system in which you want to describe the light (e.g. by putting double slits and a screen in the path), then one or the other description starts to become more appropriate, depending on which property you are trying to determine.

7. Apr 5, 2009

pillanoid

all right, thanks!