Question

Human eye requires 10 ^-17 J of energy to see an object. Calculate the number of photons required to generate the required energy. The wavelength of photon is 550 nm.

Answer 1

$$\begin{gathered} Energy=Nh\nu =Nh\frac{C}{\lambda } \\ N=\frac{E\lambda }{hC}=\frac{{10}^{-17}\times 550\times {10}^{-9}}{6.626\times {10}^{-34}\times 3\times {10}^8}=27.67photons \end{gathered}$$