A coaxial resistor of length l consists of two concentric cylinders. The inner cylinder has radius a and is made of a material with conductivity 1, and the outer cylinder, extending between r = a and r = b, is made of a material with conductivity 2. If the two ends of the resistor are capped with conducting plates, show that the resistance between the two ends is R = l / [1a2 + 2 (b2 – a2))].|