For this problem we can use 2 equations. (1) - E = mC² E = Energy of photon (J) m = Mass of photon (kg) (1.67x10⁻²⁷ kg) C = speed of light (3 x 10⁸ m/s)
(2) - E = hf E = Energy of photon (J) h = plank's constant (6.63 × 10⁻³⁴J s) f = frequency of the photon (Hz)
(1) = (2) hence, mC² = fh
by rearranging, f = mC² / h f = 1.67x10⁻²⁷ kg * (3 x 10⁸ m/s)² / (6.63 × 10⁻³⁴J s) f = 2.27 x 10²³ Hz
