Neap U4 2012 AOS 2 question 2 d help pls (I typed the question up below)

[PB]

Young modified his experiment by reducing the intensity of the incident light so that only one photon
was between the slits and the photographic plate at a time, and was still able to produce an
interference pattern.
Explain how this modification provided confirmation of the wave particle duality of light.

Answer:An individual photon/particle cannot cancel itself out or destructively interfere with itself, so
a particle model cannot be used to explain the destructive interference. 1 mark
Interference can only be explained by a wave model so this is evidence for the wavelike
nature of light. 1 mark

I think this answer is a bit dodgy? It seems like it is just answering what the NORMAL young's experiment proves, not the modified one! (cus there is no interference happening in this experiment at all since only one photon was between the screen and slits)
I am not sure how to answer this question, other than the fact that individual corpuscles display diffraction behaviour (a wave property), thus the double model duality.
Cheers.

[Alwin]

I think this answer is a bit dodgy? It seems like it is just answering what the NORMAL young's experiment proves, not the modified one! (cus there is no interference happening in this experiment at all since only one photon was between the screen and slits)
I am not sure how to answer this question, other than the fact that individual corpuscles display diffraction behaviour (a wave property), thus the double model duality.
Cheers.

Actually if you read the question carefully it tells you that interference still occurs when there is only one photon between the screen and the slits.

I don't think that it is in the study design specifically (hence the exam question tells you that it was "still able to produce an interference pattern") but most schools teach it anyways and do a quick run through of the various theories as to why and how a single photon can interfere with itself. If you've never heard of theses (remarkably interesting theories) post again, but I'll just answer your question here.

As you can see, a single photon still produces an interference pattern (wave model) and is the same as the original Young's Double Slit Experiment (shocking everyone basically). So, the same reasoning can be used aka just copy from your cheat sheet why YDS experiment supported the wave model.

So no, it's not dodgy at all

[PB]

I understand that the same spacing pattern occurs, but how can it be due to interference patterns if there is only one photon? I thought interference only occurs when two light sources clash with each other to constructively or destructively interact.
From what I have learnt, the same pattern occurs because of some weird probability distribution concept where the photon is most likely to land where the normal experiment predicts a bright fringe would appear.

[Alwin]

I understand that the same spacing pattern occurs, but how can it be due to interference patterns if there is only one photon? I thought interference only occurs when two light sources clash with each other to constructively or destructively interact.
From what I have learnt, the same pattern occurs because of some weird probability distribution concept where the photon is most likely to land where the normal experiment predicts a bright fringe would appear.

we have someone who's interested in how things work in physics. WOOOO

Okay, so there are a variety of theories:
1. The most accepted theory to date is:
The appearance of interference built up from individual photons could seemingly be explained by assuming that a single photon has its own associated wavefront that passes through both slits, and that the single photon will show up on the detector screen according to the net probability values resulting from the co-incidence of the two probability waves coming by way of the two slits.
This is akin (if you like) to quantum mechanics/chaos where a single particle can be in one place, the other, or both at the same time. (Schrödinger's cat if you like big bang theory)
Nevertheless, the key idea is that the single photon acts as a wave and interferes both constructively and destructively with itself, something the particle model does not explain.

2. Pilot theory
This one states that each electron KNOWS where to diffract to... it is also based on wave theory (and like 4 other extra dimensions irrc)

3. The theory whose name has escaped me
The photons propagate as waves and act as if there are other photons in the space between slits and screen. So, the waves will "interfere" causing the photons to strike the screen slowing building up a pattern of light and dark

something I found amusing on google

OH AND THIS LINE IS WRONG SORRY

I am not sure how to answer this question, other than the fact that individual corpuscles display diffraction behaviour (a wave property), thus the double model duality.
Cheers.

Corpuscles == particles. You're basically saying that particles hitting the slits will diffract which is true. It will look something like this where there are two bands (but not perfect because the particles will diffract slightly when they hit the edges):


The phrase that examiners are looking for is "constructive interference" and "destructive interference"!!! This is wave behaviour only, not particle


If you're really interested, a quick google came up with this: http://physicsworld.com/cws/article/news/2011/jun/03/the-secret-lives-of-photons-revealed

Theres probs much, much more out there

[PB]

           Isn't diffraction an intrinsic wave property? Unless, (if i understand correctly) you are saying that because particles have been proven to have a deBroglie wavelength, diffraction behaviour is no longer limited to waves but also particles. Thus, my argument is invalid.

[lzxnl]

           Isn't diffraction an intrinsic wave property? Unless, (if i understand correctly) you are saying that because particles have been proven to have a deBroglie wavelength, diffraction behaviour is no longer limited to waves but also particles. Thus, my argument is invalid.

You've answered your own question effectively. As particles have a wavelength, diffraction can also occur with particles when they behave as waves.

[PB]

Yeh true, I was saying that my previous argument - that diffraction behaviour is specific to waves - is invalid, not the particle diffraction one lols.
But yeh, on the other hand, I was thinking if the fact that the light particles can diffract so much is another way that the modified double slit experiment proves the wave particle duality.