ELECTROMAGNETIC INDUCTION

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ELECTROMAGNETIC INDUCTION
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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

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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.

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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.

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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.

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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

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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

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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.

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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.

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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.

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