Photon Energy Formula

Photon Energy Formula

A photon is defined as the quantum of electromagnetic radiation. The term quantum refers to the smallest elemental unit of a quantity. Hence, one quantum of electromagnetic energy is known as a 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,


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

= 19.878 x 1028 / 650×10−9

= 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

So, λ = hc / E

   = 6.626×10−34×3×108 / 350×10−10

= 19.87 x 10-28 / 350 x 10−10

= 0.056 x 10-16 m


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