Momentum density vector of a plane em wave

  • Thread starter aftershock
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  • #1
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Homework Statement



Show that in vacuum the magnitude of the momentum density
vector of a plane electromagnetic wave is equal to the energy density
divided by the speed of light, c.

Homework Equations



[itex]\vec{S}[/itex] = [itex]\vec{E}[/itex]x[itex]\vec{H}[/itex]

The Attempt at a Solution



This doesn't seem too hard if you know what a momentum density vector is, so if this should be in the introductory section I apologize but it is a hw question from an upper division course.

The only thing I'm really looking for is how to find/ what is a momentum density vector. I have no idea how to go about finding it.
 

Answers and Replies

  • #2
dextercioby
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Do you know how the 16 components of the energy-momentum tensor look like ?
 

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