Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thebrain13 on 03/11/2006 05:26:31
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I have three questions about this experiment.
Number one, what happens if you have only one slit, is there no interference pattern, just a blob which dims as you get farther from the slit?
Question number two is, how does constructive and destructive interference work? I understand the idea of adding troughs and crests together, but I dont understand how it makes sense in the context of using light, instead of using, for example, sound.
And for question number three, granted my assumption for question number one is correct, is my interpretation correct in saying that if you cover up one slit, that allows light to go places it otherwise couldn't if I leaft both open?
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1. There is an interference pattern. Look at this:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/sinslitd.html#c1
or this:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraungeo.html#c1
2. What is different with sound? Is the same concept, the only difference is the fact with sound you have longitudinal waves, with light you have trasversal waves, as in the case of waves on a liquid surface; so you can think of these, instead of light, if you prefer.
3. Yes, because the interference pattern is different. This figure should help you understand:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/dslit.html#c1
and especially this, which compare single slit, double slit and five slits diffractions:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/mulslid.html#c2
Diffraction and Interference, with light, electrons, atoms, are very fascinating topics.
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Let me rephrase my question to, if there is no slit, just openness. Is there still an interference pattern?
If so why?
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There is an interference pattern, just the results look exactly what you would expect if you weren't thinking about interference at all... A uniform distribution of light or whatever distribution your light source would produce.
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Let me rephrase my question to, if there is no slit, just openness. Is there still an interference pattern?
If so why?
An opennes is just a slit of different dimension.
Single Slit Diffraction for Different Slit Widths:
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The propagation of waves, whether through a large open window or a tiny pinhole, is controlled by Huygen's principle, which states that at any moment, each element in an existing wavefront becomes like a new radiator emitting waves anew, the total action of all of which creates the next step in the wave's propagation. The issue of phase becomes central in this matter. If you have one small loudspeaker giving a tone of say 200 Hz, the wavelength is quite a bit larger than the dimensions of the speaker, so that the wave radiates in basically all directions. (This may be dipolar, but that detail can be ignored at the moment). If you have a whole outdoor wall covered with such loudspeakers, and they all emit the same sound IN PHASE, the picture is quixte different: Each speaker tries to emit in all directions, but except for directions directly ahead, the emissions of the speakers cancel each other out, because the path lengths are all different, so, that the result is plane waves marching directly away from the wall in a collimated beam. Exactly the same sort of thing happens when light reaches an open window: At that moment, the whole wavefront is like a wall of tiny speakers all in phase, and as such, the all conspire to project the next wavefront straight through the window, and on and on until they hit the opposite wall and cast a classical image of the window opening upon it. If, however, the window is shrunk down to a tiny hole which is about the width of a wavelengty of light or smaller, that effectively shuts off all the "speakers" except one, which now radiates as does the isolated loudspeaker: over a broad range of directions, so that the light will not hit the opposite wall as a dot, but as a spread out glow covering a large area.