Bragg's Law

The path difference of a ray deflecting against the crystal layer behind another ray that deflects off the one before

$$\text{Path Difference}=2d\sin (\theta )$$

If Path Difference = $n\lambda$ for the ray, you get constructive inteference

This defines our bragg condition

$$n\lambda =2d\sin (\theta )$$

Bragg’s Law Example Question