Photon energy refers to the energy carried by an individual photon. This energy is directly proportional to the frequency of the photon and thus, inversely proportional to its wavelength.

where h is the Planck’s constant given by h = 6.62607015 x 10⁻³⁴ J/Hz (or J.s).

In terms of the wavelength, λ we can rewrite the above equation as,

Here c is the speed of light in vacuum given by c ≈ 2.99792458 x 10⁸ m/s = 2.99792458 x 10¹⁷ nm/s.

Now to convert energy in electron volts (eV), we need to convert the planck’s constant to eV.s. So, h can be written in eV.s by dividing it by the charge of electron in eV, i.e, 1.6 x 10^-19 C.

So,

On solving, we get,

Substituting the values of h and c in the above equation for energy, E we get the energy in eV as

On simplifying, we get,