when a current flows in a coil, a magnetic flux is established;
when a magnetic flux cuts a coil of wire, an e.m.f. is induced in the coil.
The above effects are involved in the process of mutual induction, illustrated in Figure 14.1, in which a changing alternating current in one coil of wire (the primary winding) induces an e.m.f. in the second coil (the secondary winding). The general principle of operation is described below.
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