# ELECTROMAGNETIC INDUCTION - PowerPoint PPT Presentation

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

4
• 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
• 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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