# Electromagnetic waves physics

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A long  straight wire of length l, radius of cross section r has resistance R. If it carries a current I ,what is the poynting vector on its surface?

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by (46.2k points)

Electric field in wire,

$E=\frac{V}{L}=\frac{IR}{L}$ (V=IR, ohm's Law)

and,

$H=\frac{I}{2\pi a}$ (current distributed along surface of wire)

$S=EH=\frac{I^2R}{2\pi aL}$

by (31 points)
Plz explain what is H. Actually I understood only that first step. Rest l didn't understand.Can u plz explain ?

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