In three dimensions, two metals A and B have the number density of free electrons in the ratio NA : NB = 1 : 3. The ratio of their Fermi temperatures TfA : TfB is:

Among the various materials related to electronics, the energy band gap is maximum in ________.

A cubic sample of edge length L is maintained at a temperature of 4 K. The speed of sound in the material of the sample is 5 × 103 m/s. The minimum value of L required to excite the lowest frequency phonon mode is closest to: