# Homework Help: X-ray diffraction

1. Feb 11, 2014

### dawud

1. The problem statement, all variables and given/known data

It's got a diagram in it so I have just attached a picture of it.

2. Relevant equations

nλ=2dsinθ

3. The attempt at a solution

I've really got no idea how to proceed with this one. I think you have to consider the effect of the thin film as well. Any ideas?

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2. Feb 11, 2014

### haruspex

From a quick reading up on the subject (of which previously I was blissfully ignorant), I would say that the incoming and outgoing beams must make the same angle to the planes in the crystal. Since it's powdered, the planes will be at every angle, but diffraction is only going to observed in those crystals with planes at the bisecting angle. So given the geometry of the source, sample and observed interference, you can deduce the angle of the crystal planes responsible.
Having done that, you can compute the plane spacing.

3. Feb 11, 2014

### BvU

3. But you can make some assumptions. You have a $\lambda$, there are 2 $\theta$s. If n= 1, what is d for each of these ?

Once again, even quick replies cross. But there is a starting point.

4. Feb 11, 2014

### dawud

Thanks a lot guys! I've got it now!