ELECTRO MAGNETIC INDUCTION

OBJECTIVES :OBJECTIVES :• IT ENABLES THE STUDENTS TO • a ) DEVELOP SCIENTIFIC INTEREST• b) ACQUIRE MORE KNOWLEDGE• ABOUT ELECTRO MAGNETIC • INDUCTION• c) DEVELOP PRACTICAL SKILL

ELECTRICITY !ELECTRICITY !

Imagine a world where there is No ELECTRICITYImagine a world where there is No ELECTRICITY ! !No lights , No trains , No personal computers.No lights , No trains , No personal computers.

The pioneering experiments of FARADAY & HENRY The pioneering experiments of FARADAY & HENRY have leadhave lead

Directly to development of modern day Directly to development of modern day generators & transformers .generators & transformers .

Civilisation as it exists today owes a great deal to Civilisation as it exists today owes a great deal to the discovery the discovery

Of ELECTRO MAGNETIC INDUCTIONOf ELECTRO MAGNETIC INDUCTION

INTRODUCTIONINTRODUCTION

The experiments of The experiments of Michael Faraday in Michael Faraday in England and of Joseph England and of Joseph Henry in U S Henry in U S A .conducted around A .conducted around 1830 demonstrated 1830 demonstrated conclusively that the conclusively that the changing magnetic field changing magnetic field produces Electrical produces Electrical fields and Electric fields and Electric currents . currents .

THE EXPERIMENT OF FARADAY &HENRYTHE EXPERIMENT OF FARADAY &HENRY

• When a bar magnet is pushed towards the coil the galvanometer deflects.This remarkable fact implies that a current has been set up in the coil in the absence of a battery. The deflection stops when the magnet is made stationary and reverses while the magnet is being pulled away from the coil

• This experiment works just as well when the coil is moved towards the magnet. .

ELECRO MAGNETIC ELECRO MAGNETIC INDUCTIONINDUCTION

It is the phenomenon It is the phenomenon of production of of production of induced emf in a coil induced emf in a coil whenever there is a whenever there is a change in flux linked change in flux linked with the coil changes with the coil changes ..

LAWS OF ELECTROMAGNETIC LAWS OF ELECTROMAGNETIC INDUCTIONINDUCTION

• 1)Whenever magnetic flux passing through a circuit changes ,an induced emf is produced whose magnitude is equal to rate of change of magnetic flux,and it lasts as long as there is a change in flux .

• 2) The direction of the induced emf is such that it always opposes the cause which produces it .

• dt

dE

ENERGY CONSERVATIONENERGY CONSERVATION

__ELECTRO MAGNETIC INDUCTIONELECTRO MAGNETIC INDUCTION

As the current starts flowing in the coil in one direction,the increase in magnetic flux induces an opposite current in the ring, The magnetic field set up by the induced current in the ring opposes the field of the coil & the repulsion between the like poles throws the ring upwards . When the current in the coil reverses its direction , the induced current in the ring aiso reverses ,& again there is a repulsion .

Self inductionSelf induction• The phenomenon

of production induced emf in a circuit due to change of current in the circuit it self is called self induction .

MUTUAL MUTUAL INDUCTIONINDUCTION

• The production of The production of induced emf in a induced emf in a coil ,whenever coil ,whenever there is a change there is a change in flux in the in flux in the neighbouring coil .neighbouring coil .

EDDY CURRENT(FOUCAULT’S EDDY CURRENT(FOUCAULT’S CURRENT)CURRENT)

The production The production of induced of induced current in a current in a solid metal solid metal blocks ,when blocks ,when the flux the flux threading threading through them through them changes .changes .

ELECTRO MAGNETIC ELECTRO MAGNETIC DEVICESDEVICES

»GENERATOR

»TRANSFORMER

A.C.GENERATORA.C.GENERATOR• It is a device which converts

mechanical energy in to electrical energy .

• PRINCIPLE :Electro magnetic induction

• Direction of induced current : Fleming’s Right hand rule.

A.C. GENERATORA.C. GENERATOR

FLEMING ‘S RIGHT FLEMING ‘S RIGHT HAND RULEHAND RULE

• Stretch the thumb , fore finger and middle finger of your right hand such that they are perpendicular to each other ,if the thumb represents the direction of motion of the coil ,fore finger represents direction of magnetic field then the middle finger represents direction of the induced current .

THEORYTHEORY• Let ‘N’ be the number of turns of the coil,• ‘B’ be the strength of the magnetic field,• ‘A’ be the area of the coil ,• Then flux associated with the coil = N B.A =NBACOS =NBACOSt• Induced emf =d/dt NBACOStBA NSIN t

TRANS FORMERTRANS FORMER

It isan electrical device which convert• High voltage Low current to Low

voltage High current & viceversa . • PRINCIPLE :Electro magnetic

induction(MUTUAL INDUCTION)• Types of trans former : 1)step up• 2)step down

TRANS FORMER A transformer consists of two

coils of insulated copper wire containing different

nu

Number of turns wound on a soft iron core . The coil to which electrical energy is fed is called primary and the coil from which the energy is drawn is called secondary .The entire magnetic flux coming out of the primary coil due to the current in it remains confined practically within the iron core and hence passes fully through the secondary.

STEP UP STEP UP TRANSFORMERTRANSFORMER

• LOW VOLTAGE HIGH CURRENT TO HIGH VOLTAGE LOW CURRENT

STEP DOWN TRANS FORMER

HIGH VOLTAGE LOW CURRENT TO LOW VOLTAGE HIGH CURRENT

TEST YOUR KNOWLEDGE1)What is electromagnetic induction ?

2) State the laws of electro magnetic induction ?

3)What is the principle of trans former ? What are the two types of transformer ?

4)What are eddy currents ? Write any three applications ?

5)With the help of neat diagram explain the principle,construction and working of an a.c.generator ?

OUR SINCERE THANKS

TO

N.V.S.

• THE DIRECTION OF INDUCED EMF IS GIVEN BY

• a) FARADAY’ LAW• b) LENZ’LAW• c) BIOT-SAVART LAW

• WHAT IS THE PRINCIPLE OF GENERATOR

• a) SELF INDUCTION• b) MUTUAL INDUCTION• C) ELECTRO MAGNETIC INDUCTION

Q 1

Q 2

Q 1

Q 2