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Hope someone can enlighten me on the following questions:

  1. In a double-slit experiment with photon, how is the photon gun aimed?

  2. If the photon gun is set up to aim at the barrier space between the two slits, is it wrong to assume the photon to hit this space consistently during each release of the photon?

  3. If the photon gun is aimed at the barrier space between the two slits, and if the distance between the slits are significantly bigger than the width of the photon gun, what would the results be like on the detector plate behind the two slits?

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  • $\begingroup$ Idk about 1 and 3, but for #2, the beam is not narrow enough that one photon will follow right behind the other. And also, the whole point of the experiment is to demonstrate particle-wave duality. If you see them more as waves, (just about) anywhere you aim some will go through, but depending on angle you might not get the interference pattern you were looking for. $\endgroup$
    – M Barbosa
    Commented Jun 12, 2016 at 1:53
  • $\begingroup$ Don't forget that even behind any sharp edge you will detect a intensity distribution patten. To see this pattern clearly one has to use a point like source and from monocromatic light. So there is an area there length gets reflected or absorbed, an area there the light gets uninfluenced and an area between there the light gets deflected in such a way, it produces fringes aka intensity distributions. $\endgroup$ Commented Jun 12, 2016 at 6:43

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The diagrams that typically figure in textbooks and pop-sci books have the transverse scale massively exaggerated. The slits for a optical wavelength version of the experiment are typically less than a millimeter apart and on order of a tenth of a millimeter or less in width.

This means that they are separated by less than the natural width of the incident beam and in a naive understanding you would naturally expect some photon to pass through each slit.

The demo version that I use in class has slits about 0.1 mm in width separated by about 0.25 mm center-to-center; the cheap laser we use to illuminate them has a spot around 2 mm in diameter, so it easily covers both slits (or several if I use a part of the apparatus where there are more present).

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