0statically and Dynamically Induced Emf

8/11/2019 0statically and Dynamically Induced Emf

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STATICALLY AND

DYNAMICALLY INDUCED EMF

Made by:Vinit Shah 61

Jaynil Patel 29

Devang Lad 30

Prem Primlani 37Guided by:

RESP KRISHNA B CHAUHAN


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Introduction to emf

EMF is shortform of electromotive force.

All the metals contain a large number of free electronswill move randomly in all the directions, inside the

metal piece.If a battery or voltage source is connected across a metalpiece then the free electrons will move in one particulardirection.

The electrical force or pressure that causes the electronsto move in a particular direction is called anelectromotive force.

The unit of emf is volt.


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Faradays law

Faradays first law: Whenever the magneticlines of force linking with the coil or conductor

changes, an emf gets induced in the coil or

conductor.

Faradays second law: The magnitude of the

induced emf is directly proportional to the rateof change of linkage.

t

N B


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Faradays law


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Direction of induced emf

The direction of induced emf and inducedcurrent in a conductor does not remain same.

It has a definite relation with the direction offlux lines and the direction of movement of theconductor.

There are two methods for decidingthedirection of the induced emf.

1. Flemings right hand rule.

2. Lenzs law.


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Flemings right hand rule

First finger point in thedirection of lines of

force, and the thumb

point in the direction of

conductor motion.

Then the second finger

indicates the directionof the induced emf.

Field

(First finger)

(thumb)

Motion

(second finger)Emf


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Lenz law

This law is stated by German scientist

Heinrich Lenz.

The direction of induced emf produced due

to the process of EMI is always such that, itwill set up a current to oppose the basic

cause responsible for inducing the emf.

tN

B

This negative sign is

due to


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Types of induced emf

There are two type of induced emf basedon the nature, they are:-

1. Dynamically induced emf2. Statically induced emf:

Further classified into:

1. Self induced emf2. Mutually induced emf


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Dynamically induced emf

An emf induced due to aphysical movement of either

conductor or flux. Here field is stationary and

conductors cut across it.

Either the coil or magnet moves. Magnitude of dynamically

induced emf is


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Magnitude of dynamically inducedemf

As shown the conductor of length l isplaced in the magnetic field produced bya permanent magnet.

The conductor moves in a plane which isparallel to the plane of the magnetic flux.Therefore induced emf is zero.

Now if the plane of direction of motion

of the conductor is perpendicular to theplane of magnetic flux then the inducedemf is maximum.

So the expression for magnitude of emf

is given by:sinBlve


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Statically induced emf

An emf is induced due to the change in theflux associated with the coil by increasing or

decreasing the current that produces flux. Conductor remains stationary and flux linked

with it changes.

Magnetic field is changing in a stationerymagnetic system.


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To produce statically induced emf

As shown ac source is connected to theelectromagnet.

Due to ac there is a change in the coilcurrent with respect to time.

This will result in alternating flux.Hence there will be change in flux w.r.t.

time. This change in flux w.r.t. time willinduce emf in this coil which is knownas statically induced emf


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Self induced emf

Due to change in flux linkage with the coil, anemf is induced into the coil as per theFaradays law. This emf is called as selfinduced emf, and this phenomenon is called asthe self induction.

The application of self induced emf is:

1. As the action of choke used with thefluorescent tube.2. As filter choke used in rectifier circuits.


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Concept of self induced emf

A coil wound on a magneticmaterial is taken. A battery along with a

variable resistor is used toadjust the current flowingthrough coil.

If we close the switch currentI starts to flow in the coil anddue to this current flux lines

are produced. Now if we change the value

of resistor the current willchange hence the flux will

change therefore emf will begenerated


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Self inductance

As per the Lenzs law, the self induced emf opposes anycurrent change taking place.

This property of the coil to oppose any change in currentflowing through it is known as the self inductance.

The expression for self inductance is:

The value of self inductance in terms of permeability:

d dIN Ldt dt


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Mutually induced emf

If the flux produced by one coil gets linkedwith another coil, and due to the change inthis flux produced by the coil one if there isemf induced in second coil then such an emf iscalled Mutually induced emf.

Applications of mutually induced emf are:

1. Induction furnaces2. Fluorescent tubes


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Concept of mutually inducedemf

Two coils are placed near to eachother.

Battery and Resistor is connectedwith coil1 so current is flowingthrough the coil1. This current canbe change by resistor.

Due to current in coil1 flux isproduced.

A part of this flux is passing throughcoil2.This flux is called mutual flux.

If we change the value of currentthen flux will change, henceaccording to Faradays law emf incoil 2 will be induced.


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Mutual inductance

It is the property due to which the change incurrent through one coil produces an emf in theother coil placed nearby.

It is denoted by M. Its unit is Henry. The expression for mutual inductance:

The expression of mutual inductance in terms ofpermeability:

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0statically and Dynamically Induced Emf