I know that when a beam of x-rays strike a crystal (covalent network lattice) that they will be reflected off in layers so that the resulting wavefront is in phase with all other waves.

 

However, i have found 2 equations that are associated with this concept and am not sure which is the correct to use.

 

Theres: {d sin(theta) = n * (lambda)} and {n * (lambda) = 2d sin(theta)}

 

Can u tell me which is the appropriate equation and what the other one would be for.

 

btw. soz for not using symbols, I would if i knew how

[math]2dSin\theta = n \lambda[/math]

 

That's the bragg diffraction equation:

 

http://en.wikipedia.org/wiki/Bragg_diffraction

 

I'm not familiar with the one without 2 in it...

The one without the 2 in it looks like Fraunhofer diffraction (e.g. through a slit). Click on the diffraction link of the Wiki article Klaynos provided.

Thanks