direction. The magnetic field around the winding is constantly
in motion. Figure 14-4 shows the magnetic field during
one cycle. Notice that the north and south poles of the
magnetic field reverse when the flow of current reverses.
Another property of electricity is important to the
operation of a transformer. When a magnetic field moves
across a wire, a voltage is induced into the wire, Figure
14-5. If the wire forms a complete circuit, current will
flow in the wire. If a second coil of wire is placed in a
moving magnetic field, then a voltage will be induced in
this second coil, Figure 14-6. This phenomenon is callec
mutual induction. Alternating current in one winding
produces a moving magnetic field that induces a voltag~
in a second winding. Electrical energy is converted into'
magnetic field and then converted back into electrica
energy in a second winding. The trick is to do this witt
little or no loss of energy.
The magnetic field loses strength quickly in air
therefore, a special steel core is used. The core is com
posed of thin sheets of a silicon-steel alloy. The mag
netic field is concentrated in the core, and energy losse
are reduced to a minimum. Figure 14-6 shows the tw<
windings separated. Most transformers have one wind
ing placed directly over the other to further reduce th(
loss of energy, as shown in Figure 14-7.