## Energy in Electromagnetic Waves Summary

- The energy carried by any wave is proportional to its amplitude squared. For electromagnetic waves, this means intensity can be expressed as
\({I}_{\text{ave}}=\cfrac{{\mathrm{c\epsilon }}_{0}{E}_{0}^{2}}{2},\)

where \({I}_{\text{ave}}\) is the average intensity in \({\text{W/m}}^{2}\), and \({E}_{0}\) is the maximum electric field strength of a continuous sinusoidal wave.

- This can also be expressed in terms of the maximum magnetic field strength \({B}_{0}\) as
\({I}_{\text{ave}}=\cfrac{{\text{cB}}_{0}^{2}}{{2\mu }_{0}}\)

and in terms of both electric and magnetic fields as

\({I}_{\text{ave}}=\cfrac{{E}_{0}{B}_{0}}{{2\mu }_{0}}.\)

- The three expressions for \({I}_{\text{ave}}\) are all equivalent.

## Glossary

### maximum field strength

the maximum amplitude an electromagnetic wave can reach, representing the maximum amount of electric force and/or magnetic flux that the wave can exert

### intensity

the power of an electric or magnetic field per unit area, for example, Watts per square meter