- #1
Physgeek64
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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