Interference of light.

  • #1
If we use a white light in Young's Double slit Experiment, instead of monochromatic light,What will happen?What could be observed on the screen?
[URL]http://C:\Documents[/URL] and Settings\Aditya\My Documents\My Pictures/untitled
 
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  • #2
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Coherent white light will cause interference but it will not be well defined!!Because there will not be distinct dark areas of zero intensity!!
 
  • #3
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when light passes through the slits and causes interference, what exactly is interfering with what?
 
  • #4
olivermsun
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Do you mean: why are the dark and light fringes called an "interference pattern"?
 
  • #5
sophiecentaur
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Fringes with white light tend to be limited to a central bright, white maximum and a fairly well defined minimum on either side. However, because the successive maxima do not coincide, you get blurred fringes of different colours and the pattern gets pretty diffuse with rainbow-coloured fringes, rather than a distinct black / white pattern.
 
  • #6
Drakkith
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when light passes through the slits and causes interference, what exactly is interfering with what?
The light is interferring with itself and with other photons (the particle that makes up light). This interference makes it so that there are areas that are much less probable for the light to strike, and will cause clear interference patterns where more light hits certain spots and less light hits others.
 
  • #7
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No one understands the "what" of light. maybe someday someone will but not right now.

Interference is the name of a phenomena. A phenomena that can be described in mathematical terms. For some experiments it is observed that light obeys that mathematics. So one of the behaviours of light is that it can exhibit interference.

There are some videos on the web of R P Feynman giving an explanation of QED. In which he makes the disticinction between understanding how something will behave and understanding what that something is.

http://vega.org.uk/video/programme/45 Feynman's book The strange theory of light and matter is worth reading too I expect your library has it.
 
  • #8
olivermsun
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when light passes through the slits and causes interference, what exactly is interfering with what?
The "simplistic" answer is that the light (viewed as waves) travels a slightly different length depending on which part of the slit it passed through and what angle it takes to the wall. Thus the light arrives at the wall as a combination of slightly different phases. The slit is important because it only allows a small "range" of paths and you can actually make out a pattern.

Don't know how much this explanation helps though, which is why I asked earlier for clarification on your question.
 
  • #9
Thanks for the video. but I;m still confused about what would be the observations on the screen.
 
  • #10
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I would expect to see coloured bands aranged symetrically about a white central line.

More accurately the superposition of what I'd see if the light is split up into numerous narrow bands of single colours of light. I'd expect to see rainbow stripes with some dark areas.

This picture http://www.britannica.com/EBchecked/media/37362/Spectrum-of-white-light-by-a-diffraction-grating [Broken] shows white light after passing through a diffraction grating.

and elsewhere on this forum https://www.physicsforums.com/showpost.php?p=2000164&postcount=4
===

As to the videos.. they explain the principles behind how to calculate with single photons. Once you have the result for a single photon accounting for its particular frequency, you can work out the result for lots and lots of photons of the same frequency. You then repeat for every(!) frequency that you will see as a part of the white light.
 
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  • #11
Thanks NOPoke!
 
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  • #12
sophiecentaur
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The light is interferring with itself and with other photons (the particle that makes up light). This interference makes it so that there are areas that are much less probable for the light to strike, and will cause clear interference patterns where more light hits certain spots and less light hits others.
Why talk of photons "interfering"?
If you want to describe what's happening, in the most straightforward way, you need to talk in terms of waves. If you really want to make a thing of it then you would need to talk in terms of probability densities for each photon and how each one affects the other one. Surprise, surprise, you get exactly the same Maths out of this approach as you do when, , treating the phenomenon as a wave phenomenon.

If you were trying to describe how you get interference in a ripple tank (exactly the same maths) you would not (would you?), in your wildest dreams. try to talk about particles so why try to introduce photons here?

Is it because you think that it is, somehow, 'better Physics'? It can't really be better because it is infinitely more long winded and gets the same result. You just have to LIVE WITH duality, I'm afraid.
 

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