1) Draw LA, TA, LO and TO phonons propagating along a one-dimensional diatomic chain (unit cell parameter, $a$), and with wavevectors $k= \pi/4a$.
2) Propose at least one approach to excite TO phonons at the edge of the 1$^{st}$ Brillouin zone using photons.
3) You decide to microwave food in a ceramic plate. After a few minutes of irradiation, you notice that the plate is hotter than the food. How is that possible? (Hint: Your explanation may require a discussion involving a phonon dispersion diagram).
