Lenz' Law describes the direction in which induced voltage
causes current to run around a loop: the voltage pushes
the current in the direction which will oppose
the change in magnetic flux through the loop.
In other words, Lenz' Law states that induced currents
try to maintain the original magnetic flux through a loop
of wire (even though they don't quite make it).
Most electrical generators turn mechanical energy
into a voltage via magnetic induction.
Lenz' Law shows why the voltage produced by such
generators alternates sign.
The maximum voltage produced by a generator of
area A rotating in a magnetic field B
at a rate of w radians per second is
V(max) = N * A * B * w
where N is the number of turns in the rotating loop.
Note that the angular velocity w (radians/second)
is related to the
period P (seconds) and frequency f (1/second)
of rotation as follows:
w = 2*pi*f = ------
Also note that the maximum voltage V(max) is 1.41 times
larger than the RMS voltage; people usually use the RMS
voltage to describe ordinary wiring, such as 120-volt circuits
in the home.