NAME MRS NEHA URKUDE SUBJECT BASIC ELECTRICAL ENGINEERING

NAME : - MRS. NEHA URKUDE SUBJECT : - BASIC ELECTRICAL ENGINEERING TOPIC : - EMF

E. M. F INDUCTION

OBJECTIVES Define Induced E. M. F. State the types of Induced EM. F. Describe Dynamically Induced E. M. F. and Statically Induced E. M. F. Explain Self Inductance and its unit. Describe Mutual Inductance and its unit.

EXPERIMENT Observe an experiment: The experimental setup consists of a coil with several turns connected to a galvanometer. Since, there is no battery or power supply, no current flows through the coil.

EXPERIMENT Now hold a magnet near or inside the coil. No current flows through the coil. • Now move the magnet towards the coil. • It is observed that there is a deflection in the galvanometer in one direction and current flows across the coil.

EXPERIMENT If the magnet is moved away from the coil, the galvanometer again shows deflection but in the opposite direction. Thus, we can conclude that a changing magnetic field produces voltage in a coil, which causes the current to flow through the coil. In short, if the magnetic flux associated with a coil is changed, voltage is produced. This voltage is known as the Induced e. m. f.

EXPERIMENT

TYPES OF INDUCED E. M. F. The change of flux can be produced in two different ways: • The conductor or coil is moved in a stationary magnetic field in such a way that the flux, which links to it, changes in magnitude. The e. m. f. induced in this way is known as dynamically induced e. m. f. For example in Generators.

TYPES OF INDUCED E. M. F.

TYPES OF INDUCED E. M. F. The conductor or coil is stationary and the magnetic field is moving. Thus, the e. m. f. induced in this way is known as statically induced e. m. f. For example, in a Transformer.

TYPES OF INDUCED E. M. F.

DYNAMICALLY INDUCED E. M. F. Consider a conductor of length ‘l’ meters. It is moving at right angles to a uniform magnetic field of flux density ‘B’ tesla.

DYNAMICALLY INDUCED E. M. F. Let ‘v’ be the velocity of the conductor in meter per second. Area = l x dx Now if the conductor is moved by a distance ‘dx’ in ‘dt’ seconds, then the area swept by the conductor is l into

DYNAMICALLY INDUCED E. M. F. Thus, the change in flux : d. Ф = Flux density x Area swept = B x ldx According to Faraday’s laws of Electromagnetic Induction, magnitude of induced e. m. f. is given by:

DYNAMICALLY INDUCED E. M. F. Dynamically induced e. m. f: Now, if the conductor is moved at an angle θ to the magnetic field, then the velocity of the conductor will be:

DYNAMICALLY INDUCED E. M. F. Therefore, Dynamically induced e. m. f. : e = Blv sinθ

STATICALLY INDUCED E. M. F A statically induced e. m. f. is divided into two types: § Self-Induced E. M. F. § Mutually Induced E. M. F.

SELF-INDUCED E. M. F • The e. m. f. induced in a coil due to the change of flux linked with it is known as self-induced e. m. f. • Consider a coil of N turns carrying the current. Thus, a magnetic field is developed across the coil.

SELF-INDUCED E. M. F • When the current flowing in the coil is changed, the flux linked with the coil also changes. • Therefore, by Faraday’s laws, an e. m. f. is induced in the coil. • This is known as self-induced e. m. f. which is given as:

MUTUALLY INDUCED E. M. F. The e. m. f. induced in a coil due to the changing current in the neighboring coil is called mutually induced e. m. f. Consider two coils P and Q which are placed adjacent to each other. A part of magnetic flux produced by coil P links with coil Q. This flux is common to both the coils and is known as mutual flux.

MUTUALLY INDUCED E. M. F. When the current flowing in the coil P is changed, the mutual flux also changes. Thus e. m. f is induced in both the coils. The e. m. f. induced in coil P is known as self-induced e. m. f. and the e. m. f induced in coil Q is known as mutually-induced e. m. f which is given as:

SELF INDUCTANCE A large number of household appliances use magnets.

SELF INDUCTANCE These appliances use electromagnets which get activated and deactivated by electricity. When electric current flows through the wire, magnetic field is set up along the wire.

SELF INDUCTANCE

SELF INDUCTANCE • We know that whenever a magnetic flux linked with a coil is changed, an e. m. f. is induced in the circuit. It causes the current to flow through the coil. • The e. m. f. induced in a coil due to the change of flux linked with it is known as self-induced e. m. f.

SELF INDUCTANCE This e. m. f. opposes the change of current in the coil. Thus the property of a coil that opposes any change in the amount of current flowing through it is known as self-inductance or inductance.

SELF INDUCTANCE When the current in the coil increases, the selfinduced e. m. f. opposes the rise of current. I. e. the direction of self-induced e. m. f. is opposite to

SELF INDUCTANCE • Similarly, when the current in the coil decreases, the selfinduced e. m. f. opposes the decrease of current. I. e. the self -induced e. m. f. is in the same direction as the applied voltage. • Note that selfinduced e. m. f. does not prevent the current from changing; it only delays the change.

SELF INDUCTANCE • The self induced e. m. f. in the coil is given as: • The magnetic flux can be expressed as: • For a circuit, as long as the permeability ‘mu’ is constant, ratio of flux to current remains constant.

SELF INDUCTANCE Therefore, rate of change of flux

SELF INDUCTANCE • • L = self inductance or inductance of the coil Finally, • • The unit of inductance is Henry. A coil has an inductance of 1 henry, if an e. m. f. of 1 volt is induced in it, when the rate of change of current in the coil is 1 ampere per second.

MUTUAL INDUCTANCE • The e. m. f. induced in a coil due to the changing current in the neighboring coil is called mutually induced e. m. f. • Consider two coils P and Q which are placed adjacent to each other. When current I 1 flows

MUTUAL INDUCTANCE A part of this flux also links with coil Q. This flux is common to both the coils and is known as mutual flux.

MUTUAL INDUCTANCE • If current in coil P changes, the mutual flux also changes and thus e. m. f is induced in coil Q. • This e. m. f. is termed as mutually induced e. m. f. Similarly, change of current in coil

MUTUAL INDUCTANCE

MUTUAL INDUCTANCE As we know that, self induced e. m. f. is responsible for self inductance. Similarly, mutually induced e. m. f. is responsible for mutual inductance. The property of one coil due to which it opposes the change in the other coil is known as mutual inductance between two coils.

MUTUAL INDUCTANCE N 1 = number of turns of coil P N 2 = number of turns of coil Q I 1 = current flowing through coil P Ф 1 = flux produced due to I 1 Ф 2 = flux linking with coil Q According to Faraday’s law, the induced e. m. f. in coil Q is given as:

MUTUAL INDUCTANCE • Now, • Permeability of surroundings is assumed to be constant and hence Ф 2 upon I 1 is constant. • Therefore, rate of change of Ф 2

MUTUAL INDUCTANCE Thus,

MUTUAL INDUCTANCE • M = mutual inductance between two coils. • The unit of inductance is Henry. • A coil has mutual inductance of 1 henry, if current changes at the rate of 1 ampere per second in one coil and induces an e. m. f. of 1 V in the other coil.

SUMMARY Defined Induced E. M. F. Stated the types of Induced EM. F. Described Dynamically Induced E. M. F. and Statically Induced E. M. F. Explained Self Inductance and its unit. Described Mutual Inductance and its unit.

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