Transcript electromagnetic induction ppt

Electromagnetic Induction
Electromagnetic Induction
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Motion of a magnet in a coil or loop
creates (induces) voltage
If coil is connected to complete circuit,
current flows
Relative motion is needed—it doesn’t
matter which moves, the magnet or the
coil
Amount of voltage depends on rate of
motion and number of loops in coil
Faraday’s Law
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The induced voltage is proportional to the
number of loops times the rate of change
of the magnetic field
Magnetic field is changed by motion or by
changing the strength of the field in an
electromagnet
Generators
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Rotating a coil in a magnetic field will
create alternating current
As coil rotates, amount of magnetic field
enclosed by loop changes, inducing a
changing voltage
Frequency of alternating current is the
same as frequency of rotation of the coil
Energy is converted from some
mechanical form to electrical
Motors and Generators
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Both have same parts
Motors convert electrical energy to
mechanical movement using the magnetic
force on a moving charge to move the coil
Generators convert mechanical to
electrical by using the magnetic force due
to the coil movement to move the charges
through the wire
Transformers
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Two coils of wire wound on the same iron
core so that changes in the magnetic field
of the first coil (primary) induce voltage
across the second coil (secondary)
If ac flows through primary, ac is induced
in secondary
Voltage in secondary depends on ratio of
turns in primary and secondary
Transformers
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If secondary has more turns, than
transformer is called step-up and voltage
is increases
If secondary has fewer turns, then is
called step-down and voltage is decreased
Power is not increased so if voltage is
stepped up, current is reduced
Transformer Equations
Primary turns
Secondary turns
=
Primary voltage
Secondary voltage
(Voltage x current)p = (voltage x current)s
Power Transmission
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Almost all electrical energy is sold as ac
because it is easy to change voltage using
transformers
High voltage and fairly low currents are
used to transmit power over long distances
This reduces losses due to heating in the
wires
Voltage is stepped down to 120 V for homes
Electric and Magnetic Fields
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Faraday’s law holds even if no conductor
is present
A changing magnetic field induces an
electrical field
Maxwell extended Faraday’s idea to say a
changing electrical field induces a
magnetic field
Electrical and Magnetic Fields
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Electrical and magnetic fields are
perpendicular to each other
Magnitude of induced field is proportional to
rate of change of the other field
Explained operation of electromagnetic
waves
Speed of light is only speed where induction
will continue without energy gain or loss