# Photon Energy Formula

TheÂ quantumÂ ofÂ electromagneticÂ radiationÂ isÂ knownÂ asÂ aÂ photon.Â TheÂ phraseÂ quantumÂ meansÂ toÂ theÂ smallestÂ elementaryÂ unitÂ ofÂ quantity andÂ oneÂ amountÂ ofÂ electromagnetic energyÂ isÂ calledÂ aÂ photon.

A photon is characterized either by wavelength (Î») 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,

$$\begin{array}{l}E = \frac{hc}{\lambda}\end{array}$$

Where

E = photon energy,

h = Planck’s constant (6.626Ã—10âˆ’34 Js)

c = speed of the light and

Î» = wavelength of the light.

Example 1

Determine the photon energy if the wavelength is 650nm.

Solution:

Given parameters are

Î» = 650nm

c = 3Ã—108Ã—108m/s

h = 6.626Ã—10âˆ’34Ã—10âˆ’34Js

Photon energy formula is given by,

E = hc / Î»

E = 6.626Ã—10âˆ’34 Ã—3Ã—108 / 650Ã—10âˆ’9

E = 19.878 x 1028 / 650Ã—10âˆ’9

E = 0.030 x 10âˆ’17J

Example 2:

If the energy of a photon is 350Ã—10âˆ’10J, determine the wavelength of that photon.

Solution:

Given parameters are,

E = 350Ã—10âˆ’10J

c = 3Ã—108m/s

h = 6.626Ã—10âˆ’34Js

Photon energy formula is given by,

E = hc / Î»

Î» = hc / E

Â Î»Â = 6.626Ã—10âˆ’34Ã—3Ã—108 / 350Ã—10âˆ’10

Î» = 19.87 x 10-28 / 350 x 10âˆ’10

Î» = 0.056 x 10-16 m