Electromagnetic Induction

Law of Electromagnetic Induction (EMI) states that a changing magnetic flux linked with a coil can generate an electromotive force and thus, electric current in the coil. Magnetic flux linked with a coil can be changed either by a relative motion between the coil and the source of magnetism or by varying the magnitude of a current producing the magnetic field. Faraday’s law of induction states that the change in flux linked with the coil is responsible for inducing emf in it. Magnetic flux of a given area is defined as the number of field lines crossing that area. Lenz’s law gives the direction of induced current in the coil. The 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. If area of a conductor placed in uniform magnetic field changes with time, the flux linked with the conductor also changes. This induces a current and hence, an emf in the conductor known as motional emf. The concept of induced current due to changing magnetic field goes well for bulk pieces of conductors. When they are placed in a changing magnetic field, induced current is produced in them. Their pattern 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 the property of a conductor due to which a change in current flowing through it induces a current in the nearby conductor. Inductance is of two types, 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. AC generator is a device used to covert mechanical energy into electrical energy. It works on the principle of electromagnetic induction i.e., when flux linked with a coil changes an emf is induced in the coil. For commercial purposes, hydro-electric and thermal generators are used. In hydro-electric generators, the mechanical energy required to rotate the generator armature is provided by falling water from height whereas in thermal generators, high pressure steam is used to rotate the generator armature.

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