1 Consider two coils placed close to each other, as shown in Figure 10.1. If you apply an AC voltage to the first (or primary) coil, the alternating current flowing through the coil creates a fluctuating magnetic field that surrounds the coil. As the strength and polarity of this magnetic field changes, it induces an alternating current and a corresponding AC voltage in the second (or secondary) coil. The AC signal induced in the secondary coil is at the same frequency as the AC signal applied to the primary coil.
Both transformer coils are usually wound around a core made of a magnetic material such as iron or ferrite to increase the strength of the magnetic field.
2 A transformer is used only with alternating currents. A fluctuating magnetic field (such as that generated by alternating current flowing through a primary coil) is required to induce current in a secondary ...