The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 1.24 ~m is incident on it. The band gap (in eV ) for the semiconductor is

Step-by-step solution

Conductivity increases when photon energy band gap energy E_g . The threshold wavelength = 1.24 m gives the minimum photon energy equal to E_g . Using E( in eV ) = 1.24 ( in m) : E_g = 1.24 1.24 = 1 eV