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The Challenge: Generate electricity

A generator 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.

magnetic field around a bar 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.

The simplest 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.

This method 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.