June 16th, 2010, 01:53 AM  #1 
Member Joined: Aug 2008 Posts: 44 Thanks: 0  Sine?
I'm (most likely) missing something ... picture: Shouldn't $\displaystyle \sin\theta=\displaystyle{\frac{d}{\frac{\Delta}{2} }}$? Last edited by skipjack; February 28th, 2018 at 03:33 PM. 
June 16th, 2010, 08:45 AM  #2 
Member Joined: Jun 2010 Posts: 36 Thanks: 0  Re: Sine?
? is the angle of incidence of xray on the crystal with respect to the surface of the crystal. To find the path difference, between two rays, you have drawn a perpendicular from one ray to the other ray. Let A be the top layer and D be the bottom layer of the crystal. Let AB and AC be the normals to the other ray. From the figure you can see that angle BAD is equal to ?. ?D = the path difference = ?/2 = ADsin? = dsin?.

June 16th, 2010, 09:47 AM  #3 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Sine? 
June 17th, 2010, 04:50 AM  #4  
Member Joined: Aug 2008 Posts: 44 Thanks: 0  Re: Sine? Quote:
PS: Aswoods, I first thought this was from some other textbook! Last edited by skipjack; February 28th, 2018 at 03:36 PM.  
June 17th, 2010, 06:51 AM  #5 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Sine?
The wave front is not horizontal. So the tiny segment between the top of the dashed line and the upper horizontal line is not part of the path difference.


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