12.2.Magnetic Phenomena and Their Interpretation 231 Variable D.C. power supply Primary FIGURE 12.6.A ring-shaped solenoid with primary and secondary windings.The magnetic flux lines are indicated by a dashed circle.Note that a current can flow in the secondary circuit only if the current (and therefore the magnetic flux) Secondary in the primary winding changes with time.An on-off switch in the primary cir- cuit may serve this purpose.A flux meter is an ampmeter without retracting Flux meter springs. ing),then the magnetization (measured in the secondary winding with a flux meter)rises slowly at first and then more rapidly,as shown in Figure 12.7(dashed line).Finally,M levels off and reaches a constant value,called the saturation magnetization,Ms.When H is reduced to zero,the magnetization retains a positive value, called the remanent magnetization,or remanence,M.It is this re- tained magnetization which is utilized in permanent magnets.The remanent magnetization can be removed by reversing the magnetic M H FIGURE 12.7.Schematic representation of a hysteresis loop of a ferromagnetic material. The dashed curve is for a newly cast piece of iron (called virgin iron).Compare to Figure 11.29.ing), then the magnetization (measured in the secondary winding with a flux meter) rises slowly at first and then more rapidly, as shown in Figure 12.7 (dashed line). Finally, M levels off and reaches a constant value, called the saturation magnetization, Ms. When H is reduced to zero, the magnetization retains a positive value, called the remanent magnetization, or remanence, Mr. It is this re￾tained magnetization which is utilized in permanent magnets. The remanent magnetization can be removed by reversing the magnetic 12.2 • Magnetic Phenomena and Their Interpretation 231 Variable D.C. power supply Primary Secondary Flux meter S A FIGURE 12.6. A ring-shaped solenoid with primary and secondary windings. The magnetic flux lines are indicated by a dashed circle. Note that a current can flow in the secondary circuit only if the current (and therefore the magnetic flux) in the primary winding changes with time. An on–off switch in the primary cir￾cuit may serve this purpose. A flux meter is an ampmeter without retracting springs. Mr Hc M Ms H FIGURE 12.7. Schematic representation of a hysteresis loop of a ferromagnetic material. The dashed curve is for a newly cast piece of iron (called virgin iron). Compare to Figure 11.29