Electricity
Information on how electric current works and details about circuit, voltage and electricity generation.
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The generator works on the remarkably simple principle that every time a wire is moved through the 'lines of force' which surround a magnet a voltage is set up in the wire and a current of electricity will flow through it, providing the ends are joined. A simple generator is a coil of wire rotating between two magnets arranged with unlike poles (a north and a south) facing each other. The current produced by the rotating coil is not steady. It is greatest when the coil is cutting straight across the lines of force (1). No current is produced when the coil is moving along the lines of force (2).
Generators
Electricity for lighting, heating, etc., is generated by what are called generators. These machines make use of the fact that when a wire moves through a magnetic field a current is set up, or induced, in the wire. In a generator the wires are arranged in a circle around a rotating shaft called the armature. The current is taken from the wires through slip rings on the shaft which make contact with two fixed carbon brushes. As the wires rotate they move downwards through the magnetic field and then upwards. This means that the direction of the induced current keeps changing - it is an alternating current. In the United States, the power supply mains use current that alternates sixty times a second: it is said to be a 60 cycles per second supply. In Britain, 50 cycles per second are used.
Direct current can be obtained by fitting a commutator instead of slip rings. This device keeps reversing the current to automatically compensate for the natural reversals. Machines of this type are called dynamos.
A practical generator has several coils placed like the spokes of a wheel to minimize the current fluctuations. They are wound on an iron core which helps to concentrate the magnetic lines of force they cut. In the diagram the iron core has been removed for clarity. The magnetic field is produced by two electromagnets (field windings).
