1. The problem statement, all variables and given/known data 11. Two parallel conductors, 1.0 cm apart, each carry 10 A of current in opposite directions. What is the magnetic field strength at the midpoint between these wires? 2. Relevant equations B = μI/ 2πr 3. The attempt at a solution I know that the magnetic field is doubled because the currents are in opposite directions. Should r = 0.01 m or 0.005 m? Is the r the distance between the two wires? I thought that r is the perpendicular distance from the wire to the point of field measurement, so that would mean 0.005 m. I think the answer in my book is wrong, because it has r = 0.01 m. Please advise.