How generator/dynamo produces electricity?

A simple dynamo is a device that converts mechanical energy into electrical energy. A coil made of conducting wire is positioned between the North and South poles of two permanent magnets. When the coil is stationary, no voltage is induced. But when the coil is rotated it experiences a changing magnetic field. rotating magnet (rotor) which distorts and cuts through the magnetic lines of flux of the stator. When the rotor cuts through lines of magnetic flux it makes electricity.

For the first half of a rotation the left side of the coil swings by the North pole of the left magnet and for the second half of the rotation it swings by the South pole of the right magnet. As a result, for the first half the coil generates a voltage with one polarity (either positive or negative) and for the second half the voltage has the opposite polarity. This type of voltage − one that switches between positive and negative − is called alternating voltage