19.2. The Electric Generator http://www.ck12.org
magnetic field lines), the flux through the loop begins to increase. This is analogous to moving the north pole of a
magnet toward the loop. The induced current, therefore, reverses direction, producing magnetic field lines opposing
the permanent magnet field, again obeying Lenz’s law.
We can see, then, that every half-turn of the loop reverses the direction of the induced current. Electric generators
typically producealternating current(AC). Most of the alternating current produced in the United States has a
frequency 60 Hz. That is, the induced current reverses direction twice each cycle or 120 times per second. In
Europe, the standard frequency is 50 Hz.
Generating alternating current is much more energy efficient (and therefore cheaper) than using direct current.
However, many electrical devices require DC voltages and currents in order to operate. Power transformers are
used to solve this problem.