In the last 5 minutes, where Prof took the example of a 1-D crystal. He drew the E-k diagram for that sample and said that diffraction occur at all the the point where wave vector touches the bragg plane or brillouin zone. But in this case the wave vector is not any external EM wave or electron wave rather it is the wave vectors of electrons confined in crystal. How did he used the result derived for a beam falling on sample for the electrons confined in the crystal? This is very confusing, can some one explain it?
