### Dynamo

A dynamo is a device that converts mechanical energy into electrical energy. The structure of a simple dynamo. 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. This induces a voltage within the coil.

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.  It has typical sinusoidal-shaped alternating voltage generated in the dynamo coil. The height of the sinusoidal wave, which represents the strength of the voltage induced in the coil, depends on the strength of the magnetic field, the number of loops in the coil, and the speed at which the coil rotates .

The spinning coil of the dynamo is connected to the circuit that it powers using a commutator  The commutator consists of two half-cylinders of smooth conducting material that are separated by a small gap. Each half-cylinder is permanently attached to one end of the rotating coil, and the commutator rotates with the coil. Two stationary brushes, usually made of carbon, press against the spinning commutator. The brushes act as the terminals (outputs) of the dynamo.

In addition to acting as the terminals of the electricity-generating coil, the commutator performs another very important function. It keeps the dynamo’s generated voltage from alternating between positive and negative. Each brush slides along the two halves of the commutator, switching halves the instant the voltage in the coil reverses polarity.

This ensures that the voltage produced by the dynamo is no longer fluctuating between positive and negative, but is instead always positive. This type of voltage is called direct voltage, and is shown by the curve . This process, where alternating voltage is converted to direct voltage, is called rectification .

##### Working of Dynamo

Faraday’s law of electromagnetic induction – is a basic law of electromagnetism predicting how change in magnetic field will interact with an electric circuit to produce an electromotive force (EMF)—a phenomenon called electromagnetic induction. To be completely accurate, if the magnetic flux through a coil is changed, a voltage will be produced. This voltage is known as the induced emf. The magnetic flux is a measure of the number of magnetic field lines passing through an area.

A dynamo consists of rotating knob, permanent magnet and wire coils. The rotating knob is placed against the rim of the Tyre. So when the wheel rotates it rotates the knob which rotates the magnet which is surrounded by the coil. When the magnet rotates its magnetic flux through the coil starts varying which induces emf in the coil according to Faraday’s law of electromagnetic induction. The induced voltage is used to power headlights in front of the cycle.