Alternating current (AC)

AC means that the electric current (voltage) is changed both in direction and in magnitude as a function of time. Sinusoidal type is the most common.

In generator (dynamo) the relative orientation of the magnet and the loop is changed leading to change in magnetic flux. Note the two affects of change in rotational speed to the induced current.

Sinusoidal signal is produced by a loop rotating at constant angular is speed in a uniform magnetic field. The magneitude varies between peak values, r.m.s. value being the effective value.

In the AC circuit the power dissipated (to heat etc) in the resistor varies as a function of time, since the current varies. If the mean power over one cycle was equal to the resistor placed in the DC circuit, the DC current would be equal to the r.m.s. value of the AC current.

Hence, if a resistor of 50 ohm is placed in DC circuit it produces heat at the rate of 50 W when 1 A current flowing. In an AC circuit the same 50 W is produced by the same resistor if approximately 1,4 A in peak value is flowing.