# How do you calculate the frequency and wavelength of an absorbed or emitted photon?

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The energy absorbed or emmited by the photon is related to the photon frequency. Hence, the evaluation of the frequency of a photon can be done by means of the following equation, such that:

`E = f*h`

"E" represents the energy of the photon and "f" represents the frequency of the photon. If the frequency is calculated, then it is possible to find out the wavelength of the photon, such that:

`f = c/lambda`

"`lambda` " represents the wavelength, "`f` " represents the freqeuncy and "`c` " represents the velocity of light.

The equation that expresses the relation between photon energy, frequency, wavelength and atomic state transitions is the following, such that:

`Delta E = E_f - E_i = (-13.6 eV) (Z^2)/(n_f^2) - -13.6 eV) (Z^2)/(n_i^2)`

Z expresses the number of protons, `n_f` expresses the final state of energy and `n_i ` expresses the initial state of energy.