Electricity and Magnetism
Interrelation between Electricity and Magnetism
The theory that electric current flowing through a conductor produces a magnetic field around it was discovered by Oersted, in 1819 AD. This showed that magnetism can be generated through electricity. After the discovery of this theory, scientists are dealing with the problem of how to bring about the reverse effect i.e. how to produce electricity from magnetism. After a series of experiments, in 1831 AD Michael Faraday, it was discovered that it was possible to obtain electric current in a circuit from a magnetic field.
Magnetic Flux and Its Variation
The magnetic lines of force start from the North Pole of the magnet and enter the South Pole externally. Internally, these lines of force move from the South Pole to the North Pole. Hence, the magnetic lines of force are always closed. Let’s suppose, a bar magnet is placed at rest facing the North Pole towards a coil. Some magnetic lines of force will pass through the coil while going from its North Pole to South Pole. The number of lines of force passing through the surface of the coil is a measure of lines of force through this surface as shown in figure (a).
The number of magnetic lines of force passing through the surface held perpendicular to these lines of force is said to be magnetic flux through a surface.
The magnetic flux through the surface of the coil increases either if the magnet or the coil is moved closer to one another as shown in figure (a). This is because the number of magnetic flux through the surface of the coil increases in this case. Similarly, it decreases when they have moved away from each other as shown in figure (b).
Some Electric Appliances