The problem statement, all variables and given/known data I'm given an infinite cylinder with radius a. There's a uniformal current density j flowing in the cylinder in the z direction. I'm asked to find the magnetic field in the following ways -Ampere's law -Magnetic potential and then use it to calculate the magnetic field. The attempt at a solution Calculating the magnetic field by Ampere's law wasn't a problem. I got stuck on the second part a little. The attempt is in the file below. Help ASAP will be very much appreciated since I have to hand this homework tomorrow. Thank you!