William W. answered • 09/14/19

Experienced Tutor and Retired Engineer

Photon energy is calculated using Planck's postulate which is written as E = hf, where E is photon energy in Joules; h is Planck's constant (6.626x10^-34 Joule seconds); and f is the frequency of the light in hertz.

The frequency of 280 GHz is 280x10^9 Hz.= 280x10^9 sec^-1

So E = (6.626x10^-34 Joule seconds)(280x10^9 sec^-1) = 1,855x10^-22 joules, Rounding this to 2 sig figs gives E = 1.9x10-22 joules