This is a question directly from a homework sheet, however I can\'t find any dec

Question

This is a question directly from a homework sheet, however I can't find any decent answers online so hopefully someone can help!

In single slit diffraction, why is the central maximum double the width of the other bands and the brightest?

I understand vaguely that it is something to do with Fresnel zones, but I'm quite confused. Instead of making another question, I think this question also fits in with the above:

Why does the intensity of light bands decrease away from the central maximum in single slit diffraction?

Thanks!

Explanation / Answer

A more physical way of restating Ron's answer: in diffraction theory you are adding up Huygens wavelets over the aperture with appropriate phase factors. The central fringe is the only one where the entire aperture is adding in phase, i.e. constructively. The next fringe will have 2/3 adding constructively and 1/3 destructively, then after that 3/5 - 2/5, etc. The farther out you go in fringes, the more of the aperture is just cancelling itself.

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