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# Double/Single slit diffraction Watch

1. I'm writing a report on diffraction and a little confused on the conditions for a minimum/maximum given for single and double slit diffraction.

I know for single slit diffraction, conditions for minima are given by , and that the equation for maximum for double slit diffraction is given by , but aren't these the same equations? So why do they give different results i.e. maxima for one, and minima for the other?

And for single slit diffraction, wouldn't give the conditions for maxima as well as for minima?
2. The equation normally given for the double slit case is

y is the fringe separation. That is, the distance between two adjacent bright or dark fringes on a screen a distance d from the sources. The sources are a distance a apart. There is no "n" in the formula.

The single slit equation is for an angle and is usually given as

(or just theta if the angle is very small)

and is the angular position of the n th minimum. The equation is derived for destructive interference where the path difference is half a wavelength. Hence the lambda / 2 in your formula.
Here a is the width of the single slit.
There is no "d" in the formula.

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Updated: April 16, 2013
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