7.1 Electromotive Force 303 Problem 7.4 Suppose the conductivity of the material separating the cylinders in Ex. 7.2 is not uniform; specifically, σ(s) =k/s, for some constant k. Find the re- sistance between the cylinders. [Hint: Because σ is a function of position, Eq. 7.5 does not hold, the charge density is not zero in the resistive medium, and E does not go like 1/s. But we do know that for steady currents I is the same across each cylindrical surface. Take it from there.]

7.1 Electromotive Force 303 Problem 7.4 Suppose the conductivity of the material separating the cylinders in Ex. 7.2 is not uniform; specifically, σ(s) =k/s, for some constant k. Find the re- sistance between the cylinders. [Hint: Because σ is a function of position, Eq. 7.5 does not hold, the charge density is not zero in the resistive medium, and E does not go like 1/s. But we do know that for steady currents I is the same across each cylindrical surface. Take it from there.]