# Formula: Photon Energy    Wavelength

## Photon energy

Unit
Photon energy is the energy of a single photon (light particle). You can calculate it using the wavelength of light $$\lambda$$. For example, if the light has the wavelength $$\lambda = 550 \, \mathrm{nm}$$, then the energy of a photon is: \begin{align} W_{\text p} &= 6.6 \cdot 10^{-34} \, \mathrm{Js} ~\cdot~ \frac{ 3 \cdot 10^{8} \, \frac{\mathrm m}{\mathrm s} }{ 550 \cdot 10^{-9} \, \mathrm{m} } \\\\ &= 3.6 \cdot 10^{-19} \, \mathrm{J} \end{align}

## Wavelength

Unit
Wavelength of the electromagnetic radiation. Radio waves, for example, have a long wavelength. X-rays, for example, have a short wavelength.

## Planck's Constant

Unit
Planck's constant is a physical constant from quantum mechanics and has the value: $$h ~=~ 6.626 \, 070 \, 15 \,\cdot\, 10^{-34} \, \mathrm{Js}$$

## Speed of light

Unit
Speed of light (in vacuum) is a physical constant and has the value: $$c ~=~ 3 \cdot 10^8 \, \frac{\mathrm m}{\mathrm s}$$

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