a) Calculate the momentum of a photon that has a wavelength of 4.2m. b) Below is the band structure of a semiconductor material that has 275meV direct band gaps at the Lpoint in momentum space. The interatomic spacing in the directions for this material is 0.53 nm. Indicate the absorption of a 4.2m photon on the diagram below. Show that such an interband electronic transition in this material will have very little change in momentum when displayed on this band diagram