The wavelength of a beam of light is 1.20 cm. what is the energy of one photon of this radiation?

Photon energy is the energy carried by a single photon with a certain wavelength and frequency. These terms are related by an equation.

E = hv

where h is the Planck's constant (6.626 x 10-34 J s), v is the frequency which is related to the wavelength by:

λv = c where λ is the wavelength and c is the speed of light (3.00 x 108 m/s)

Therefore, the energy equation

E = hc / λ

E = (6.626 x 10-34 J s) (3.00 x 10^8 m/s) / 0.0120 m = 1.657 x 10^-23 J