Question

Derive Poynting vector expression for a straight wire of resistance R carrying a current I having length L.

Answer 1

Since,

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)

so, magnitude of poynting vector, $\overrightarrow{s}.$

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