We all know, Bragg's law , [tex]n\lambda=2dsin\theta[/tex](adsbygoogle = window.adsbygoogle || []).push({});

where [tex]2dsin\theta=path difference[/tex].

In the derivation of the path difference we take the two incident rays to be parallel which is perfect BUT we takereflectedrays also to be parallel.How can this be since the reflected rays have toMEETfor superposition to take place.

This is the same as in FRAUNHOFER diffraction, where we CAN take parallel rays due to the distance being effectively infinity or due to the use of LENS.

But we are not using a lens nor is the distance supposed to be very large(infinity) in the experimental methods of Xray diffraction ( rotating crystal, powder photograph etc.).

So, how is it that this formula works?

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# Bragg's law

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