Electrical generators or dynamo are the machines used to convert mechanical energy into electrical energy.They are based on the principle of electromagnetic induction. This note explains about electromagnetic induction and Faraday's laws for electromagnetic induction.
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).
Whenever the magnetic flux linked with a closed circuit changes, an emf is induced in the circuit, called induced e.m.f. This phenomenon is called electromagnetic induction. The resulting current by electromagnetic induction is called induced current.
Faraday’s laws of electromagnetic induction or principle of electromagnetic induction
This law was propounded by an English physicist named Michael Faraday in 1831 AD. It is also called the principle of generators. It states that: -
∴ Induced e.m.f. \(\propto\) Rate of change of magnetic flux
Some Electric Appliances
Electrical generators or dynamo are the machines used to convert mechanical energy into electrical energy. They are based on the principle of electromagnetic induction. A dynamo is used to induce current in fewer amounts and a generator is used to induce electric current in large scale.
It should be noted that the name generator is actually a misnomer, as no energy is being generated by it but is only converted from one form to another. A generator or dynamo converts kinetic energy into electrical energy.
Faraday's laws of electromagnetic induction are: -
What is electromagnetic induction?
Whenever the magnetic flux linked with a closed circuit changes, an emf is induced in the circuit, called induced e.m.f. This phenomenon is called electromagnetic induction.
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