Question

The intensity of radiation from a human body is maximum around a certain wavelength. A photon of this wavelength can just excite an electron from the valence to the conduction band of a semiconductor used in a night vision device. Assume that the black body radiation law holds for the human body. The band gap of such a semiconductor is close to
(A) 0.1 eV (B) 0.5 eV (C) 1.0 eV (D) 2.0 eV

Answer 1

The intensity of radiation from a human body is maximum at 12 micron wavelength

So,
f=c/l
f=3*10^8/12*10^-6
f=0.25*10^14

Energy=hf
=6.636*10^-34*0.25*10^14
=1.659*10^-20 J
=0.1 eV
(1 J=6.242*10^18eV)

so answer is a) 0.1 eV