We were talking about X-ray diffraction from crystal lattices in class
yesterday. The interference that shows the maxima comes from reflection
from the different planes if I read / understand correctly. So one of my
bright students asks "why" is it called diffraction? Thin film
interference is not called diffraction and yet it is interference due to
reflections.
I had no answer. Why is it called diffraction? Or is my understanding of
the process flawed?