The figure shows the reflection of a plane wave by two neighbouring atoms on the surface of a crystal. The depicted waves are actually de-Broglie wave of electrons accelerated from rest by a potential difference of V volt. Neglect relativistic effects and take mass and charge of an electron to be m and e respectively. Calculate `phi` for the case of a constructive interference.

Answer

`phi = sin^(-1) ((nh)/(dsqrt(2 meV)))`