In a straight coaxial cable, the central conductor and the outer conductor transport equal currents in opposite directions. The magnetic field vanishes

Step-by-step solution

By Ampere's circuital law, the line integral of the magnetic field around any closed loop is proportional to the net current enclosed by the loop: B d l = ₀ I_ enclosed For a straight coaxial cable, consider a circular Amperian loop of radius r outside the cable ( r > R_ outer ). The central conductor carries a current I in one direction, and the outer conductor carries an equal current I in the opposite direction. The net current enclosed by the Amperian loop outside the cable is: I_ enclosed = I - I = 0 Substitut