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## Homework Statement

A long straight wire of radius a and resistance per unit length R carries a constant current I. Find the Poynting vector N = E × H at the surface of the wire and give

a sketch showing the directions of the current, the electric field E, the magnetic field

H, and N. Integrate the Poynting vector over the surface of a length l of the wire and comment on your result

## Homework Equations

## The Attempt at a Solution

##\integral{H\dot dl}=I_{free}##

##H(2\pi r)=I##

##H|_a=\frac{I}{2\pi a} \hat{\theta}##

E outside the wire will be ##E=-\frac{\lambda}{2\pi\epsilon r } \hat{r}##

I don't know if this is the same as the E field at the surface? Also I don't know how to get ##\lambda## in terms of I and R

then ##S=E\cross H ##

Many thanks