일반물리학 2 — Magnetic Fields Due to Currents: Problem 56

56 In Fig. 29-60, two concentric circular loops of wire carrying current in the same direction lie in the same plane. Loop 1 has radius 1.50 cm and carries 4.00 mA. Loop 2 has radius 2.50 cm and carries 6.00 mA. Loop 2 is to be rotated about a diameter while the net magnetic field set up by the two loops at their common center is measured. (a) Through what angle must loop 2 be rotated so that the magnitude of that net field is 200 nT? (b) What is the least possible magnitude of the net field?