The Debye model correctly predicts the low temperature dependence of the heat capacity, which is proportional to T^3 the Debye T 3 law. Just like the Einstein model , it also recovers the Dulong–Petit law at high temperatures.
Q. What is the basic assumption of Debye theory?
In contrast to the Einstein theory of specific heat, which assumes that each atom has the same vibrational frequency, Debye postulated that there is a continuous range of frequencies that cuts off at a maximum frequency νD, which is characteristic of a particular solid.
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Q. What are the basic assumptions on which Debye theory is based?
1) The atomic displacements are considered to be a system of transverse and longitudinal elastic waves within a continuous uniform solid. 2) All the waves are assumed to have normal velocity that are appropriate to longitudinal and transverse waves in the solid.
Q. What is the theory of specific heat capacity?
Informally, it is the amount of energy that must be added, in the form of heat, to one unit of mass of the substance in order to cause an increase of one unit in temperature. The SI unit of specific heat capacity is joule per kelvin per kilogram, J⋅kg−1⋅K−1.
Q. What is the unit of Debye temperature?
The Debye temperature indicates the approximate temperature limit below which quantum effects may be observed. At temperatures T ≫ θD the specific heat of a crystal consisting of atoms of one type at constant volume is Cr = 6 cal (°C. mole)-1, which agrees with Dulong and Petit’s law.
Q. What is the Debye cutoff frequency?
The Debye frequency cut occurs when the wavelength of the phonon frequency reaches the size of the smallest unit of the lattice which is the length of the unit cell.
Q. Are phonons heat?
At each frequency, quantum mechanics principles dictate that the vibrational energy must be a multiple of a basic amount of energy, called a quantum, that is proportional to the frequency. Physicists call these basic levels of energy phonons. In a sense, then, “phonon” is just a fancy word for a particle of heat.
Q. What is acoustic branch?
The acoustical branch is qualitatively similar to the dispersion relation for a monatomic lattice, but the optical branch represents a completely different form of wave motion. For acoustical branch (in the long wavelength limit) the displacement of both atoms has the same amplitude, direction and phase.
