The energy contained in a photon is given by the formula E = hf, where h is the Planck constant and f is the frequency of the photon. Since h = 4.110−15 eVs, f = E/h = 1.0103 eV / (4.110−15 eVs) = 2.11017s-1. Note: if the Planck constant is provided in J*s is suffices to divide by the elementary charge to obtain the value used here.