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What is intensity

  1. Jul 24, 2014 #1
    Definition/Summary

    Intensity of radiation = power per area perpendicular to the radiation. It is a vector, parallel to the radiation.

    Intensity of radiation = energy density times velocity (therefore sometimes called energy flux).

    It is measured in watts per square metre ([itex]Wm^{-2}[/itex])

    Equations

    For a surface perpendicular to the radiation:

    [itex]I\ =\ P/area[/itex]

    For a general surface, with normal [itex]\hat{\mathbf{n}}[/itex]:

    [tex]P\ =\ \int_S \mathbf{I}\cdot\hat{\mathbf{n}}\,dS[/tex]

    Extended explanation

    Power per area = energy density times velocity:

    Power = energy per time (measured in [itex]W\ =\ Js^{-1}[/itex]).

    Power per area = energy per area per time = energy density (ie, per volume) times velocity.

    So intensity = power per area = energy density times velocity.

    * This entry is from our old Library feature. If you know who wrote it, please let us know so we can attribute a writer. Thanks!
     
  2. jcsd
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