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No of possible normal modes of vibration equal to no of unit cells in crystal

Answer»

In physics, a phonon is a collective excitationin a periodic, elastic arrangement of ATOMS or molecules in condensed matter, like solidsand some liquids. Often designated a quasiparticle,[1] it represents an excited statein the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.

Phonons PLAY a major role in many of the physical properties of condensed matter, like THERMAL conductivity and electrical conductivity. The study of phonons is an important part of condensed matter physics.

The concept of phonons was INTRODUCED in 1932 by Soviet physicist Igor Tamm. The name phonon comes from the Greek word φωνή (phonē), which translates to sound or VOICE because long-wavelength phonons give rise to sound. The name is based on the word photon.

Shorter-wavelength higher-frequency phonons are responsible for the majority of the thermal capacity of solids.


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