The Challenge: Generate electricity
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is simply a device that converts mechanical energy (itself derived from
coal, oil, natural gas, wind, water, nuclear reactions or other sources)
into electrical energy. Here, we describe how to use readily available materials
to make a simple generator. Although it will only be powerful enough to
light a small torch bulb, it works on the same basic principles as the power
station generators that supply domestic electricity.
How a Generator Works
When an electric current
flows through a wire, it generates a three-dimensional magnetic force field
around the wire, similar to that surrounding a bar magnet. Magnets are also
surrounded by a similar three-dimensional field. This can be "seen"
in two dimensions if iron filings are sprinkled on a sheet of paper placed
over the magnet. The filings align themselves along the lines of magnetic
force surrounding the magnet.
Two-dimensional representation of the magnetic field around a bar magnet. The arrows indicate
the direction of the lines of magnetic force. The N (north) and S (south)
indicate the poles of the magnet, where the lines of force are focused.
The north pole of the magnet will repel the north pole of a compass or
another bar magnet, while its south pole will attract the north pole of
a compass or another bar magnet.
generator consists of just a coil of wire and a bar magnet. When you push
the magnet through the middle of the coil, an electric current is produced
in the wire. The current flows in one direction as the magnet is pushed
in, and in the other direction as the magnet is removed. In other words,
an alternating current is produced. If you hold the magnet absolutely still
inside the coil, no current is generated at all. Another way of producing
the current would be for the magnet to be rotated inside the coil, or for
the coil to be rotated round the magnet.
of generating electricity, called induction, was discovered by Michael Faraday
in 1831. He found that the stronger the magnets were, the more turns of
wire in the coil, and the quicker the motion of the magnet or coil, the
greater the voltage produced. Faraday also observed that it was more efficient
if the coil was wound around a metal core, as this helped to concentrate
the magnetic field.
The Rough Science generators