Note on Electromagnetic Induction

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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

  1. Inverter
    An inverter is an electronic appliance which stores electric current when electricity is supplied. It is very popular in our daily life, as it is used as the source of electric current during the time of load shedding. It changes the flow of alternating current into direct current stored in the batteries connected to it. When the electric supply is turned off, the stored direct current in the battery is changed into the alternating current by the device. It can be conveniently used in our daily works.

  2. Battery Charger
    In the present days, the battery chargers are used in many electric appliances. The appliances are also supplied with batteries that store direct current. It changes the alternating current that is supplied in the batteries into direct current which helps to run the electronic devices. It is also called recharger. There are different types of charger with the different system. The system disconnects the electric circuit when the device is fully charged.

  3. Solar Battery
    Solar battery is an electric device that changes light energy into electrical energy. It is also called a solar panel which may be fixed or movable. A solar panel is the group of solar cells. It stores the electrical energy in a storing cell i.e. lead acid battery. The stored electrical energy can be used for different purposes as a source of electricity.

  4. Adapter
    An adapter is an electric device that is used to run radio and other electrical appliances which need less voltage to work. It changes the voltage of A.C. supply into D.C. voltage. In it, a knob is used to adjust the required voltage for the electric appliance to be run.

  1. Electric current flowing through a conductor produces a magnetic field around it.
  2. The magnetic flux through the surface of the coil increases either if the magnet or the coil is moved closer to one another due to the increase in the number of magnetic flux through the surface of the coil.
  3. The magnetic flux decreases when they have moved away from each other.
  4. Whenever there is a change in the magnetic flux linked with a closed coil, an e.m.f. is induced in the wire of the coil; this phenomenon is called electromagnetic induction and the current induced by this method is called induced current.
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