A long cylindrical wire of radius R and conductivity σ, lying along the z-axis, carries a uniform axial current density I. The Poynting vector on the surface of the wire is (in the following \(\widehat{\boldsymbol{\rho}}\) and \(\widehat{\varphi}\) denote the unit vectors along the radial and azimuthal directions respectively)
1
\(\frac{I^2 R}{2 \sigma} \widehat{\boldsymbol{\rho}}\)
2
\(-\frac{I^2 R}{2 \sigma} \widehat{\boldsymbol{\rho}}\)
3
\(-\frac{I^2 \pi R}{4 \sigma} \widehat{\varphi}\)
4
\(\frac{I^2 \pi R}{4 \sigma} \widehat{\boldsymbol{\varphi}}\)