1. The problem statement, all variables and given/known data A circular disk of radius r and thickness d is made of material with resistivity p . Show that the resistance between points a and b (Fig. attached)is independent of r and is given by R=πp /2d 2. Relevant equations R= p L / A where L and A are length and section area respectively . 3. The attempt at a solution I tried to use differential equations , but I always end up with ∞ or some indeterminate forms .