Question

What is the energy of a photon of light of wavelength 0.645 µm?

Answer 1

The energy of a photon is given by:\[E=h \nu \]where E is energy; h is Planck's constant; and ν is frequency. Your problem is in terms of wavelength, but you can handle that because we also know that:\[c=\lambda \nu \]where c is the speed of light; and λ is the wavelength. Now you should be able to write an equation relating energy to wavelength by using the two equations above.

Pay close attention to units, especially the units of Planck's constant.