Assignment:
What is meant by the terms: (i) normal mode and (ii) phonon. Explain why phonons obey Planck-Bose/Einstein statistics. What is the difference between an acoustic mode, and optic mode?
Quantized lattice vibrations are called phonons. When a phonon propagetes to a crystal lattice the atomic oscillators excited and vibrate as per the propagation of phons in the lattice. there is a relation called dispersion relation , connecting teh frequency and veleocity of propagation of teh phonons. the phonons creates two modes of vibrations, optic and accoustic. In between these two modes of vibrations there is a region wher no sound waves are propagated, and such a lattice acts as a bandpass mechanical filter. This problem is illustrated.