Electron Volt to Joule Conversion Example Problem

Worked Chemistry Problems

Blue glass globe filled with bright plasma lines.
Blue glass globe filled with bright plasma lines. Getty Images/Clive Streeter

This example problem demonstrates how to convert electron volts to joules.

When working with energy values typical for the atomic scale, the joule is too large of a unit to be effective. An electron volt is a unit of energy suited to energies involved in atomic studies. The electron volt is defined as the total amount of kinetic energy gained by an unbound electron as it is accelerated through a potential difference of one volt.

The conversion factor is 1 electron volt (eV) = 1.602 x 10-19 J


A red photon with a wavelength of 621 nm has 2 eV of energy. What is this energy in joules?


x J = 2 eV x 1.602 x 10-19 J/ 1 eV
x J = 3.204 x 10-19 J


The energy of a 621 nm photon is 3.204 x 10-19 J.