Three photodiodes `D_1 , D_2 ` and `D_3` are made of semiconductors having
band gaps of ` 2.5 eV , 2 eV` and 3 eV , respectively . Which one will be able to detect light of wavelength ` 6000 Å ` ?

Explanation

Given wavelength of light `lamda = 6000 Å = 6000 xx 10^(-10) m`
Energy of the light photon
`E = (hc)/(lamda) = (6.6 xx 10^(-34) xx 3 xx 10^(8))/(6000 xx 10^(-10) xx 1.6 xx 10^(-19)) eV = 2.06 eV`
The incident radiation which is detected by the photodiode havin genergy should be greated than the band-gap. So, it is only valid for diode `D_(2)`. Then, diode `D_(2)` will detect this radiation