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Polynting vectors vecS is defined as a v...

Polynting vectors `vecS` is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propogation. Mathematically, it is given by `vecS=1/(mu_0) vecExxvecB`. Show the nature of S vs t graph

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In em wage let `vecE` be varying along y-axis, `vecB` is along z-axis and propagation of wave be along x-axis.
Then `vecExxvecB` will tell the direction of propagation of energy flow in e.m. wave, along x-axis.
Let `vecE==E_0sin(omegat-kx) hatj`.
`vecB=B_0 sin(omegat-kx)hatk`
`vecS=1/(mu_0) (vecExxvecB)=1/(mu_0) E_0B_0 sin^2 (omegat-kx)[hatjxxhati]`
`=(E_0B_0)/(mu_0)sin^2(omegat-kx)hati`
The variation of `|vecS|` with time t will be as shown in fig,. By thick solide curve.
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