Table of contents :

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S. No. Contents Page No.

(From- To)

1. Introduction of Induction 4

2. Faraday & Henry experiment 5-8

3. Self Induction & Mutual Induction 8-14

4. Applications & Future Use of Self Induction &

Mutual Induction

15-21

5. Conclusions 22

6. References 23-24

1. INTRODUCTION

What is INDUCTION?

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Induction simply means generation or production. In physics, it is the process of generating

electric current in the conductor by placing the conductor in the changing magnetic field. It is

called because current is said to be induced in the conductor by the magnetic field. When

induction occurs in an electrical circuit and affects the flow of electricity it is called inductance.

Joseph Henry, an American physicist discovered Induction & investigated how current in one

circuit induces current in the another.

2. FARADAY & HENRY EXPERIMENT [III]

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It all started through a series of experiments carried out by Faraday & Henry. Faraday’s Law of

Induction was discovered through experiments carried out by Michel Faraday in 1831 and by

Joseph Henry in the United States at about the same time.

The experiments performed by them are described below:

Experiment 1

When the N-pole of the bar magnet was pushed towards the coil,

the galvanometer showed a deflection indicating the presence of

electric current in the coil. The deflection continued as long as the

bar magnet was in the motion. The galvanometer showed no

deflection when the bar magnet was held stationary.

Similarly, when the bar magnet was moved away from the coil, the

galvanometer showed a deflection but in the opposite direction.

Indicating the reversal of the current’s direction.

Thus, it was proved by the experiment that it was the relative

motion between the magnet and the coil responsible for the

generation (production) of electric current.

(fig 1)[1] (fig 2)[2]

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Experiment 2

In the second experiment, bar magnet was replaced by another coil

& was connected to a battery producing a steady current and a

steady magnetic field.

When the second coil was moved towards the first coil, there was a

deflection seen in the galvanometer. When the coil was moved

away, the deflection was observed in the opposite direction.

Thus it proved that, it was the relative motion between the coils

that induced the electric

field.

(fig 3)[3]

Experiment 3

In the third experiment, first coil was connected to a sensitive

galvanometer and the second one through a battery through a

tapping key.

When the key is pressed, galvanometer shoed a deflection & then

returned to zero. When it is released, it again showed a deflection

but in the opposite direction.

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(fig 4)[4]

Thus all the experiments performed by these genius minded

scientists brought a conclusion that electric current can be induced

in a coil by flux change in another coil or in itself. Induced emf

appears in the coil whenever the amount of magnetic flux linked

with the coil changes.

In both the cases , ΦB is proportional to I.

ΦB α I

Where ΦB is the magnetic flux associated with the coil.

For a closely wound coil of N turns,

NΦB α I

where NΦB is the magnetic flux linkage.

NΦB α I

NΦB = L I

L = NΦB/IHere L is called the Inductance.

Thus inductance is the measure of the flux linkage produced by the

inductor per unit of current.

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Its SI unit is Henry & it depends upon

Geometry of the Coil

Intrinsic material properties.

3. SELF INDUCTION & MUTUAL INDUCTION

I. SELF INDUCTION: It is the property of the coil due to which the coil

opposes any change in the strength of current flowing through it by inducing an

e.m.f in itself. In other words, it is the production of the emf on changing the

current in a coil in itself.

The property of the self inductance is a particular form of the electromagnetic

induction. In the case of self induction, the magnetic field created by a changing

current in the circuit itself induces a voltage in the same circuit. Therefore, the

voltage is self induced.

(fig 5)[5]

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Coefficient of Self Induction

Let I is the current flowing through the coil at any time.

Φ be the magnetic flux linked with all the turns of the coil at that

time.

We also know that,

Φ α I

Φ =LI

Here L is a constant of proportionality & is called coefficient of

self- induction or self inductance of the coil. L varies with number

of turns of the coil, area of cross-section of the coil & nature of

material of the coil.

If I =1A

Then Φ =L or, L= Φ

hence, the coefficient of self induction of the coil can be

numerically defined as the amount of magnetic flux linked with the

coil when 1 ampere of current flows through the coil.

Now, by faraday’s law:

E= -d Φ/dt

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E= -d(LI)/dt

or, E= -LdI/dt (self induced emf)

Self Induction of a Long Solenoid

(fig 6)[6]

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The magnetic field around a long solenoid is given by

B = μNI/l

Where μ is magnetic permeability of free space, N is the

total number of turns in the solenoid.

Therefore, magnetic flux through each turn of the solenoid is

B X Area of each turn

= (μNI/l) A

Therefore, ϕ = (μNI/l) A N

But ϕ = LI

Therefore, LI = (μNNA)/l

I. MUTUAL INDUCTION: When one circuit induces current flow in a

nearby circuit, it is known as Mutual Induction. It is the property of two coils due

to which each opposes any changes in the strength of current flowing through the

other by developing an induced emf.

(fig 7)[5]

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(fig 8)[6]

On pressing the key, current in A increases from zero to maximum value. It takes

some time to reach to the maximum value. During this time (rise of current)

current is continuously increasing hence the magnetic flux associated with the A

also increases. Since B is nearby to A, magnetic flux associated with it also

increases. Thus an emf is induced in the coil and according to the Lenz’s Law, the

induced current in B would oppose increase in current in A by flowing in a

direction opposite to the cell current in A.

Similarly, on releasing the key, the current in the coil A decreases hence the

magnetic flux associated with it decreases. As B is nearby, so magnetic flux

associated with B also decreases and hence an induced emf is developed. The

direction of the induced current would be in the direction of the cell current so as

to oppose the decrease in the current.

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(fig 9)[7]

(fig 10)[8]

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Coefficient of Mutual Induction

Let Φ be the magnetic flux linked with all the turns of the

neighbouring coil.

I be the current in the coil.

We know that,

Φ α I

=> Φ =MI

Here M is a constant of proportionality & is called coefficient of

mutual- induction or mutual inductance of the two coils.

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4. APPLICATIONS & USE OF SELF and MUTUAL INDUCTION

The applications of this Induction are everywhere. In transformers, AC’s, eddy currents etc. It is

only this induction which is basis even for electric guitars which completely changed the face of

the whole music world. In details, the applications are discussed below.

I. Inductive Transducers : The inductive pick-up transducers

are mainly used for displacement or position measurement.

Example of inductive pick-up based transducer is LVDT ( Linear

Variable Differential Transducers) .

LVDT is similar to transformer sharing a common core & a

primary winding.

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(fig 11)[9]

The two secondary coils are connected opposite to each other. The

connection is in such a way that the outputs of the two coils are

added together simply by connection. The secondary coils are

connected in the center of the primary coils. From an Oscillator, an

AC current or voltage is applied in the primary coil.

The two secondary coils are connected in such a way that when the

core is at the centre position, equal voltage signal is induced in

both the coils. When the core is displaced right or left, the no. of

turns in the secondary coil exposed to the primary coil changes.

Thus any movement in the core causes the Mutual Inductance of

each secondary coil to vary relative to the primary coil. The

variations of mutual inductance of each coil, in effect, induce

varied relative voltage in the secondary coils. Since the two

secondary coil windings are connected in opposite, as the core

moves, the output of one increase and other decrease.

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(fig 11)[10]

(fig 12)[10]

Fig 12 shows the Cross-Sectional View of LVDT Core and

Windings.

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II. Asynchronous AC Motors : An induction motor (or

asynchronous motor) is a type of alternating current motor where

power is supplied to the rotor by means of electromagnetic

induction. The induction motor was invented by Nikola Tesla in

1882 in France.

The basic difference between an induction motor and a

synchronous AC motor is that in the latter a current is supplied

onto the rotor.

(fig 13)

The principle of operation of AC motors is similar regarding interaction of the

magnetic fields, but commutation is not required. The rotor winding of the

asynchronous AC motors have no external voltage applied; rather, voltages

are induced in the rotor windings due to the rotating fields around the stator.

The rotor rotates at slower speed than the rotary stator fields (called slip)

making the induction possible, hence the term asynchronous. Due to this,

these are sometime called Induction machines.

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Induction motors are preferred due to their rugged construction, absence of

brushes (which are required in most DC motors) & the ability to control the

speed of the motor.

(fig 14)

(A 3-phase power supply provides a rotating magnetic field in an induction motor.)

III. Transformer : Transformers are used to increase or decrease

AC voltages & currents in the circuits

The transformer is based on two principles: firstly, that an electric

current can produce a magnetic field (electromagnetism) and

secondly that a changing magnetic field within a coil of wire

induces a voltage across the ends of the coil (electromagnetic

induction).

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The basic principle involved in a transformer is Mutual Induction.

A change in the current in the primary coil changes the developed

magnetic flux. Thus a voltage is induced in the secondary coil by

the changing magnetic flux.

(fig 15)[11]

A magnetic field is created by the current passing in the primary

coil. The primary and secondary coils are wrapped around a core

of very high magnetic permeability.

The voltage induced across the secondary coil is

-----------------(1)

Where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the magnetic flux.

Since the same voltage passes through both primary and secondary coils, the instantaneous voltage across the primary is given by

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------------------(2)

Dividing equation 1 by equation 2, we get

(it is the basic equation for the stepping up or stepping down.)

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5. CONCLUSIONS

The observations led by Michael Faraday and other scientists revealed another face of our

universe how it works. Applications of this Induction is almost everywhere. It is the basis of the

many basic amenities required in day-to-day life. For example electric generators that power

cities and transportation lines. Induction furnace which is used in industries to melt metals at

large scale also makes use of this induction.

How about a life without machine or without electricity or even without entertainment? Simply

horrible! It’s simply tough for we machine aligned & dependent human to compromise with life

without these things. Imagine a life without electricity. Ironically, earth would be Black Hole.

Make your head turn around and you will see Induction around you.

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6.REFERNCES

Websites:

1. http://www.radioelectronicschool.net/files/downloads/faradyanim.gif

2. http://images.google.co.in/imgres?imgurl=http://faraday.ee.emu.edu.tr/EENG331/ faraday1.png&imgrefurl=http://faraday.ee.emu.edu.tr/EENG331/main.htm&usg=__9kgwLtZwX76sZ_lx6v_QtoOnk4I=&h=300&w=500&sz=16&hl=en&start=3&tbnid=VpDIuqE150fZWM:&tbnh=78&tbnw=130&prev=/images%3Fq%3Dfaraday%2527s%2Belectromagnetic%2Binduction%2Bexperiment%26gbv%3D2%26hl%3Den%26sa%3DX

3. http://images.google.co.in/imgres?imgurl=http://www.daviddarling.info/images/ electromagnetic_induction.jpg&imgrefurl=http://www.daviddarling.info/encyclopedia/E/electromagnetic_induction.html&usg=__QfqqTMyjlWospNDLdWNVXMD4A0g=&h=479&w=500&sz=115&hl=en&start=73&tbnid=s7Na9HB7r2E3XM:&tbnh=125&tbnw=130&prev=/images%3Fq%3Dfaraday%2527s%2Belectromagnetic%2Binduction%2Bexperiment%26gbv%3D2%26ndsp%3D21%26hl%3Den%26sa%3DN%26start%3D63

4. http://images.google.co.in/imgres?imgurl=http://micro.magnet.fsu.edu/electromag/electricity/ images/inductance/faraday.jpg&imgrefurl=http://micro.magnet.fsu.edu/electromag/electricity/inductance.html&usg=__yRu4wuVZn62Iz6eUSEf_XZEeu-k=&h=231&w=350&sz=22&hl=en&start=7&tbnid=kqzvy612_scv1M:&tbnh=79&tbnw=120&prev=/images%3Fq%3Dfaraday%2527s%2Bexperiment%26gbv%3D2%26hl%3Den%26sa%3DG

5. http://www.rfcafe.com/references/electrical/Electricity%20-%20Basic%20Navy%20Training %20Courses/images/Figure%20116.jpg

6. http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/ selfinductance.htm

7. http://hyperphysics.phy-astr.gsu.edu/Hbase/magnetic/imgmag/indmut2.gif

8. http://content.tutorvista.com/science/CBSEXScience/Ch534/images/img31.jpeg

9. http://www.me.utexas.edu/~dsclab/labs/forcemotion/Lvdt1.gif

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10. http://images.google.com/imgres?imgurl=http://zone.ni.com/cms/images/devzone/tut/a/ f841fe69729.gif&imgrefurl=http://zone.ni.com/devzone/cda/tut/p/id/3638&usg=__6KNl7dFNTBYj2FljaQduMS9GqZE=&h=276&w=375&sz=12&hl=en&start=11&tbnid=MWHxGZQKtqfj1M:&tbnh=90&tbnw=122&prev=/images%3Fq%3DLINEAR%2BVARIABLE%2BDIFFERENTIAL%2BTRANSFORMER%26gbv%3D2%26hl%3Den%26sa%3DX

11. http://en.wikipedia.org/wiki/File:Transformer3d_col3.svg

Books:

I. Resnick R; Halliday D; Krane K. , Physics, John Wiley, Ed 5/Vol 2, 2005, Page-775;776

II. Resnick R; Halliday D; Walker J. , Physics, John Wiley, Ed 8, 2008, Page-805;806;814

III. Gomber K; Gogia K., Pradeep’s Fundamental Physics, Ed 17, 2008, Page-4/4; 4/11; 4/12; 4/13; 4/14

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