College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 71

Two coplanar and concentric circular loops of wire carry currents of I 1 = 5.00 A and I 2 = 3.00 A in opposite directions as in Figure P19.65. (a) If r 1 = 12.0 cm and r 2 = 9.00 cm, what are (a) the magnitude and (b) the direction of the net magnetic field at the center of the two loops (c) Let r 1 remain fixed at 12.0 cm and let r 2 be a variable. Determine the value of r 2 such that the net field at the center of the loop is zero.