INDUCTANCE Inductance is the ability to induce an electromagnetic current. Mutual inductance is the induction of one device upon another. The current passing through one set of coils can transmit energy to a second coil next to it. This is what happens in a transformer, although transformers are more efficient. The cause of the induction is the rate of change of the current through one device acting on another. The equation for this is seen in figure 135:
Figure 135
The larger the mutual inductance, the more effective is the induction between the two. The units for mutual inductance are the Henry, which is ohm-seconds. Transformers are efficient inductors so there is a large mutual inductance. Electric dryers have too high a mutual inductance so there is counter-winding of the coils that cancel out the magnetic field produced. Self-inductance can also occur. When the current through a coil changes, it creates a magnetic field and flux, inducing a counter emf as is required by Lenz’s law. The induced emf is related to the geometry of the device as well as the rate of change of the current. Any device that can self-induct is called an inductor. Induction always opposes the changes in current. This means that there is opposition to rapid change within an
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