Text: [SOLID STATE] "A sound quantum. The energy of a phonon is hv, where h is Planck's constant and v the frequency of vibration of the sound wave. The phonon is thus analogous to the photon, a light quantum. The concept of a phonon as a packet of sound waves, the wave packet having particle-like aspects, is particularly convenient in the theory of the thermal conductivity of insulators, where one may speak of a phonon gas, collisions between phonons, and a phonon mean free path. In the theory of the properties of superfluid helium, the quanta of longitudinal sound waves in the liquid helium are called phonons. " The quantized lattice vibration, or phonon, which can be interpreted as a quantized sound wave since it travels through a quantum solid or fluid, or through nuclear matter, in the same manner as sound goes through air. (3)

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Source: 3