15. In BZ(I) of the ID monatomic lattice (a) the number of normal modes is equal...
15. In BZ(I) of the ID monatomic lattice (a) the number of normal modes is equal to the number of the allowed values of (b) the group velocity increases with increasing a (c) the vibrational motions of the atoms are equivalent (a) , and -correspond to the same normal mode 16. A transverse elastic wave is travelling in a continuous medium in 1D. For this wave (a) the velocity depends on Young's modulus (b) the density of states is constant (c) the dispersion relation is sinusoidal (d) all of the above 17. For a wave travelling in 3D in an elastic medium (a) each wavenumber corresponds to 3 vibrational modes (b) the density of states is nonlinear in w (c) the number of vibrational modes increases with the dimensions of the crystal (d) all of the above 18. A longitudinal elastic wave is travelling at velocity 4.45 x 103 m/s in a crystal of density 3.8 g/cm. The Young's modulus for this crystal is (a) 7.53 x 107 kg/m 2 (b) 7.53 x 100 kg/m s?