Bragg's law
1.33 λ path difference · I = 6% of maximumScattering geometry
Reflected waves
Intensity against angleclick to set θ
Bragg's law
X-rays reflect weakly from each plane of atoms in a crystal. The beam reflected from one plane down travels an extra distance 2d sin θ, so all the reflections add up in phase only when .
The intensity plot shows the interference of N planes, with . A real crystal has millions of planes, which is why diffraction peaks are so sharp.