I have been driving myself crazy trying to figure out this problem, for a while now. I just can't get the right answer. should the number of turns be multiplied or divided by the radius? Please help me out. Two circular coils, concentric and lying in the same plane, produce magnetic fields such that the net magnetic field is zero at the center. The number of turns and radius are 5 and 10.00 cm for the inner coil, and 3 and 13.8 cm for the outer coil. What is the magnitude and direction (positive for counterclockwise, negative for clockwise) of the outer current if the inner current is 2.00 A and counterclockwise ?