Electromagnetic Induction

•    Law of Electromagnetic Induction (EMI) states that an electromotive force can be generated in a coil by changing magnetic flux linked with the coil, thus, producing an electric current in the coil. There are two ways of changing magnetic flux linked with a coil. First, providing a relative motion between the coil and the source of magnetism; second, by varying the magnitude of a current producing the magnetic field.


•    Magnetic flux of a given area is defined as the number of field lines crossing that area. Faraday’s law of induction relates the change in flux and induced emf. Faraday’s law of induction states that the change in flux linked with the coil is responsible for inducing emf in it.


                                             

•    The direction of induced current in the coil is given by Lenz’s law. The Lenz’s law states that the direction of induced emf and hence that of induced current in the coil is such that it always opposes the change in the flux that produces it. Lenz’s law is consistent with the law of conservation of energy.

•    Motional emf in a conductor is induced as a result of induced current in it. A current is induced in the conductor if area of the conductor placed in uniform magnetic field changes with time. With the changing area, the flux linked with the conductor also changes inducing an electric current in it.
The pattern of induced current in conductors resembles the swirling eddies in water and hence such currents are called eddy currents. Eddy currents are used in magnetic braking systems and induction furnaces.


•    Inductance is defined as the property of a conductor due to which a change in current flowing through it induces a current in the nearby conductor. There are two types of inductance - mutual inductance and self-inductance.
Self inductance is defined as the induction of a voltage in a current carrying wire when the current in the wire itself is changing.
Mutual inductance is the induction of voltage in a secondary coil due to the magnetic field generated by in primary coil.


•    A device called AC generator works on the principle of electromagnetic induction. An AC generator is used to covert mechanical energy into electrical energy.
Hydro-electric and thermal generators are used for commercial purpose. In hydro-electric generators, falling water from a height is used to provide the mechanical energy required to rotate the generator armature whereas high pressure steam is used to rotate the generator armature in thermal generators,

 

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