Photon Energy Formula

The quantum of electromagnetic radiation is known as photon. The phrase quantum means to the smallest elementary unit of quantity and one amount of electromagnetic energy is called photon.

A photon is characterized either by wavelength (λ) or an equivalent energy E.

The energy of a photon is inversely proportional to the wavelength of a photon.

The Photon energy formula is given by,

Photon energy formula


E = photon energy,

h = Planck’s constant (6.626×10−34 Js)

c = speed of the light and

λ = wavelength of the light.

Example 1

Determine the photon energy if the wavelength is 650nm.


Given parameters are

λ = 650nm

c = 3×108×108m/s

h = 6.626×10−34×10−34Js

Photon energy formula is given by,

E = hc / λ

E = 6.626×10−34 ×3×108 / 650×10−9

E = 19.878 x 1028 / 650×10−9

E = 0.030 x 10−17J

Example 2:

If the energy of a photon is 350×10−10J, determine the wavelength of that photon.


Given parameters are,

E = 350×10−10J

c = 3×108m/s

h = 6.626×10−34Js

Photon energy formula is given by,

E = hc / λ

λ = hc / E

 λ = 6.626×10−34×3×108 / 350×10−10

λ = 19.87 x 10-28 / 350 x 10−10

λ = 0.056 x 10-16 m


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