Halliday, Resnick & Walker — Magnetic Fields: Problem 58

58 Fig. 28-41a, two concentric coils, lying in the same plane, carry currents in opposite directions. The current in the larger coil 1 is fixed. Current \(i_2\) in coil 2 can be varied. Figure 28-41b gives the net magnetic moment of the two-coil system as a function of \(i_2\). The vertical axis scale is set by \(\mu_{net,s} = 2.0 \times 10^{-5} \text{ A} \cdot \text{m}^2\) and the horizontal axis scale is set by \(i_{2s} = 20.0 \text{ mA}\). If the current in coil 2 is then reversed, what is the magnitude of the net magnetic moment of the two-coil system when \(i_2 = 7.0 \text{ mA}\)?