![](c01_fig17.jpg)
Figure 1.17(a) A bar magnet creates a dipolar field with north and south poles. (b) A dipolar field can also be produced by electric currents flowing through a coil of metallic wire, as shown for this battery-powered electromagnet. (c) Earth’s magnetic field, which is approximately dipolar above Earth’s surface, is produced by electric currents flowing in the liquid-metal outer core, which are powered by convection.