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ELECTROMAGNETIC INDUCTION

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ELECTROMAGNETIC INDUCTION ELECTROMAGNETIC INDUCTION Can a magnet produce electricity? Oersted s experiments showed that electric current produces magnetic field. – PowerPoint PPT presentation

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Title: ELECTROMAGNETIC INDUCTION


1
ELECTROMAGNETIC INDUCTION
2
ELECTROMAGNETIC INDUCTION
  • Can a magnet produce electricity?
  • Oersteds experiments showed that electric
    current produces magnetic field.
  • Michael Faraday discovered that when a magnet and
    a coil of wire are in relative motion wrt each
    other a current is induced in the coil.
  • This phenomenon is called
  • electromagnetic induction

3
Faradays Experiment
  • A coil of wire is connected to a galvanometer.
  • A magnet is moved into the coil and taken out.
  • The galvanometer shows deflection.

4
Faradays observations
  • Induced current is produced-
  • whenever there is relative motion between the
    coil and the magnet.
  • The strength of the induced current depends on
    the rate of relative motion.
  • When the coil and magnet are at rest relative to
    each other there is no induced current.

5
What is the cause of induced current?
  • Whenever there is relative motion between
  • the coil and the magnet there is a change
  • in the magnetic flux linked with the coil.
  • When current through a coil continuously
    changes also a current is induced in a
    neighboring coil
  • The change in flux is the cause of induced
    current in the coil.

6
Faradays Laws of Electromagnetic Induction
  • 1.Whenever there is a change in the magnetic flux
    linked with a coil a current is induced in it and
    the induced current exists as long as the change
    in flux exists.
  • 2. The strength of the induced current is
    proportional to the rate of change of flux.
  • I a d?/dt

7
Direction of induced current
  • The direction of induced current is so as to
    oppose the change in flux.
  • I - d?/dt
  • The direction is given by Lenzs Law
  • For a coil of N turns induced current is
  • I - N d?/dt

8
Lenzs Lawand conservation of energy
  • Whenever the magnet is moved wrt coil work is
    done against either a force of attraction or
    repulsion . This work done is converted to
    Electrical energy.
  • When the N pole of magnet is moved towards coil
    induced current is anticlockwise.

9
METHODS OF PRODUCING INDUCED CURRENT
  • Induced current is produced whenever the magnetic
    flux linked with a coil changes .The change in
    flux can be brought about in three ways.
  • The magnetic flux linked with a coil is ? B A
    sin?.
  • Flux changes when (i ) B changes ( ii ) A
    changes
  • ( iii ) ? changes. (? is the angle between B
    and the outward drawn normal to the plane of the
    coil).
  • When there is relative motion between coil
    and magnet
  • B changes.

10
Induced e.m.f by changing area of coil linked
with a magnetic field
  • PQRS is a coil in a uniform magnetic field B.
    Side PQ is movable. Let PQ move with a velocity V
    through a small distance x. dA/dt l dx/dt -lv
  • The e.m.f induced in the coil is E - d?/dt -
    B dA/dt Blv If the resistance of the coil is R
    then induced current is I Blv/R.

11
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