The energy e of an electron in the conduction band of a metal is related to its wave vector k by: e = a sinº ka, where a is a constant and a is the atomic lattice spacing. if a = 2 x 10-10 m then the fermi wave vector is 2.618 x 100 m-1 and fermi energy is 1 ev. determine the effective mass of conduction electrons at the fermi level. (1) (b) a thin, pure (intrinsic) semiconductor is found to transmit light in the infra-red, but as the frequency of the light is increased, the semiconductor suddenly becomes absorptive. suggest a reason for this phenomena. (c) derive an equation for the conductivity of an intrinsic semiconductor, using con- cepts such as the fermi level, the band-gap, mobility, carrier density and fermi- dirac distribution. assume a constant density of states for electrons and holes.