(Multiple Choice)

(1)

A metal is a good conductor because the valence energy band for electrons is 

(a) Completely full. 

(b) Full, but there is only a small gap to a higher empty band. 

(c) Partly full. 

(d) Empty. 

(e) None of these is correct.

(2)

Insulators are poor conductors of electricity because 

(a) There is a small energy gap between the valence band and the next higher band where electrons can exist. 

(b) There is a large energy gap between the full valence band and the next higher band where electrons can exist. 

(c) The valence band has a few vacancies for electrons. 

(d) The valence band is only partly full. 

(e) None of these is correct.

(3) True or false: 

(a) Solids that are good electrical conductors are usually good heat conductors. 

(b) The classical free-electron theory adequately explains the heat capacity of metals. 

(c) At T = 0, the Fermi factor is either 1 or 0. 

(d) The Fermi energy is the average energy of an electron in a solid. 

(e) The contact potential between two metals is proportional to the difference in the work functions of the two metals. 

(f) At T = 0, an intrinsic semiconductor is an insulator. 

(g) Semiconductors conduct current in one direction only.