A dynamo is a device that converts mechanical energy into electrical energy. For example, power for bicycle lamps used to be provided by a type of dynamo in which a ribbed cylinder resting against the bike tire was made to rotate as the cyclist pedaled along.
The two main components of a dynamo are a system for producing a magnetic field (a stator) and a coil of conducting wire (an armature) that rotates in such a way that the wires continually cut through the magnetic field lines. The end product is an alternating current flowing through the wires. A third component, a commutator (a set of contacts mounted around the machine's rotating shaft) is often used to convert the alternating current into a direct current.
There is a close relationship between dynamos and electric motors. One converts movement into electric current; the other, electric current into movement. In fact, traction motors on modern electric locomotives are often used for both tasks.
English chemist and physicist Michael Faraday (1791-1867) was responsible for the invention of a whole range of electromagnetic rotary devices, and he produced the first dynamo, in 1831. American inventor Joseph HenTy (1797-1878) produced a similar prototype around the same time. These demonstration devices soon gave way, in 1832, to a more effective machine devised by a French instrument maker, Antoine-Hippolyte Pixii (1808- 1835). Working according to Faraday's, Pixii rotated a permanent magnet so that its poles passed by a piece of iron wrapped with wire; with each turn of the magnet, electricity passed along the wire.
