Q 12-14-023NEETJEE MainMedium
Three photodiodes $D_1$, $D_2$ and $D_3$ are made of semiconductors with band gaps $2.5$ eV, $2.0$ eV and $1.4$ eV respectively. Light of wavelength $600$ nm falls on each. Which of them can detect it? ($hc = 1240$ eV nm)
Answer: (C) $D_2$ and $D_3$ only
Photon energy $= \dfrac{1240}{600} \approx 2.07$ eV.
A photodiode detects light only if the photon energy is at least the band gap. $2.07$ eV exceeds $2.0$ eV and $1.4$ eV but not $2.5$ eV, so only $D_2$ and $D_3$ respond.
Solution by Sreeraj P, M.Sc Physics