1. The problem statement, all variables and given/known data A long copper rod 8 cm in diameter has an off-center cylindrical hole 4 cm in diameter down its full length. This conductor carries a current of 900 amps flowing in the direction “into the paper.” What is the direction, and strength in tesla, of the magnetic field at the point P that lies on the axis of the outer cylinder? (To clarify, point P is in the center of the big cylinder, and the small cut-out cylinder is tangent to the edge of the big cylinder and touches point P at the top). 2. Relevant equations B(r) = mu*I / 2pi*r 3. The attempt at a solution I used superposition of currents, saying that the cut out cylinder is equivalent to a cylinder carrying 900 A out of the page superposed on the big cylinder carrying 900 A into the page. The magnetic field due to the small superposed cylinder is mu*900 / (2pi*0.02) = 9*10^11 T. I didn't know how to handle the magnetic field from the big cylinder, however, since point P is at the center, which means r=0. Any ideas?