A laser produces 22.0 mW of light. In 3.00 hr, the laser emits 4.53*10^20 photons. What is the wavelength of the laser?

Energy of a photon can be calculated from the product of the Planck's constant and the frequency of the light. We can calculate the wavelength from the frequency that we can obtain. We do as follows:

E = hv

22000 (3) (3600) = 6.26x10^-34 (v)

v = 3.7955x10^41

wavelength = c/v = 3x10^8 / (3.7955x10^41) = 7.90x10^-34 m