An air-filled coaxial cable consists of a metal wire of diameter d surrounded by a thin metal sheath of diameter D. When the wire is charged, deduce expressions for the electric field E(r) and electric potential V(r) at a radial distance r (d/2 < r=””>< d/2)=”” from=”” the=”” central=”” axis.=”” hence=”” deduce=”” the=”” capacitance=”” per=”” unit=”” length=”” of=”” the=”” cable.=””>
The breakdown field strength of air is 3 Mv m-1. If d = 1 mm and D = 1cm, calculate the potential difference between wire and sheath at which electrical breakdown occurs.