(a) Classify as conductor, semiconductor or insulator: copper (bands overlap), silicon (Eg = 1.1 eV), diamond (Eg = 5.5 eV). (b) Why does a silicon chip conduct better when heated, while a copper wire conducts worse? Solution: (a) Copper: conductor. Silicon: semiconductor. Diamond: insulator. (b) Heating gives more silicon electrons enough energy to jump the 1.1 eV gap → more carriers → better conduction (negative temperature coefficient). In copper, heating increases lattice vibrations that scatter the already-free electrons → higher resistance (positive temperature coefficient).