File:Poynting vector coaxial cable.svg

English: Poynting vector in a coaxial cable, as well as the fields it is derived from. Poynting vector shows the direction and rate of energy flow (red arrows into the page). The inner and outer conductors are shown in gray, and the dielectric is shown in white. Current in the inner conductor is flowing into the page. Current in the outer conductor is flowing out of the page. No electric field exists inside the conductors, so the Poynting vector in the gray areas is zero. The magnetic fields of inner and outer conductors cancel outside of the cable, so the Poynting vector outside the cable is also zero. This means that the energy flow is confined to the dielectric region between the conductors.