# How can I calculate the wavelength from energy?

##### 1 Answer
Jul 11, 2014

To calculate the wavelength, you need to know either the frequency or the energy of the radiation.

Wavelength from frequency

You can find the relation between wavelength and frequency at

http://socratic.org/questions/how-are-wavelength-and-frequency-of-a-wave-related

For example, what is the wavelength of a radio wave with a frequency of
590 kHz?

fλ = c

λ = c/f = (2.998 × 10⁸"m·s⁻¹")/(590 × 10³"s⁻¹") = 508 m

Wavelength from energy

The formula is

E = (hc)/λ or λ = (hc)/E, where $h$ is Planck's constant.

For example, what is the wavelength of a photon that has an energy of
3.36 × 10⁻¹⁹ J?

λ = (hc)/E = (6.626 × 10⁻³⁴"J·s" × 2.998 × 10⁸"m·s⁻¹")/(3.36 × 10⁻¹⁹"J") = 5.91 × 10⁻⁷ m =
591 nm