If pieces of copper and germanium are cooled from room temperature to $77 \ K$,their resistance will:

At $0 \ K$,a piece of germanium:

In a semiconductor,which of the following statements are correct?
$(i)$ There are no free electrons at $0\, K$.
$(ii)$ There are no free electrons at any temperature.
$(iii)$ The number of free electrons increases with temperature.
$(iv)$ The number of free electrons is less than that in a conductor.

State the conductivity of metals and resistivity of insulators.

$A$ pure semiconductor behaves slightly as a conductor at

Is the ionisation energy of an isolated free atom different from the ionisation energy for the atoms in a crystalline lattice?