If a semiconductor photodiode can detect a photon with a maximum wavelength of 400 nm, then its band gap energy is
Planck's constant $\mathrm{h}=6.63 \times 10^{-34} \mathrm{~J} . \mathrm{s}$.
Speed of light $\mathrm{c}=3 \times 10^8 \mathrm{~m} / \mathrm{s}$
