PHY592 Lattice Vibration

Lattice disturbance in solid with large wavelength, lambda >>a can be represented by elastic travelling waves with wavevector, q and frequency (omega).

• True

• False

Periodic boundary condition means that any wave in this e^ikr is required to have the same value for a position r and it has r+L. Spacing between allowed point in k-space can be represents as?

• L/2pi

• 2pi/L

• pi/2L

• 2pi/a

The Debye sphere in the Debye Model shows that

 $\omega=Vs.q$  . Physical meaning of Debye Sphere can be explain as below statement except?

• The radius of the sphere is q and is related to the Debye sphere frequency

• The Debye sphere contains no vibrational states in solid

• No vibrational states exist outsides the Debye sphere

Which physicist found and stated that the heat capacity of many solid elements is about 3r and also the specific heat capacity of any solid multiply by its atomic weights is a constant with an approximate value of 25Jmol^-1K^-1?

• Debye

• Einstein

• Dulong& Petit

• Hookes

Einstein Model assume that atoms vibrate with certain constant frequency as in simple harmonic motion

• True

• False

As referred to above figure ,Choose the correct statement below related to energy and momentum for the dispersion diagram.

• only momentum is conserved, while energy is not conserved

• only energy is conserved, while momentum is not conserved

• Both energy and momentum is not conserved

• Both energy and momentum is conserved

What is normal modes?

• A single motion where particle move at different frequency

• A periodic collective motion where all particles move at the same frequency

• A periodic collective motion where all particles move at the different frequency

Monoataomic lattice is the one with same type of atom

• True

• False

The diatomic lattice...

• in which the unit cell is either composed of two same atom

• in which the unit cell is either composed of two different atoms

In optical branch, all atoms in the unit cell moves in phase with each other (at q=0)

• True

• False