b) A coaxial cable is constructed from a central cylindrical conductor of radius a carrying current I and a concentric conducting cylindrical shell with inner radius b and outer CONFIDENTIAL 202304/BSC107A radius c with a current of I in the opposite direction (Figure 2). Assume that the currents are distributed uniformly over the cross sections of each conductor. i. Derive an expression for the magnitude and direction of the magnetic field at point ac. [2 marks] iv. What is the advantage of using the coaxial cable as compared to a long straight wire? [2 marks] Figure 2