# How do you calculate the energy of a photon with an electromagnetic wave of wavelength 420 nm?

Jun 6, 2017

The energy of a photon of frequency $\nu$ is given by,

$E = h \nu$ where $h$ is the Planck's constant.

Also, we have the general relationship for waves,

$\nu l a m \mathrm{da} = c$ where $l a m \mathrm{da}$ is the wavelength and $c$ is the speed of the wave.

This gives, $\nu = \frac{c}{l a m \mathrm{da}}$

Plugging it into the expression for energy,

$E = h \frac{c}{l a m \mathrm{da}}$

Thus, plugging in the numerical values,

$E = 4.73 \cdot {10}^{- 19} J$ Or $E = 2.95 e V$