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Summarizing Energy in Electromagnetic Waves

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.


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


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

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