C H A P T E R 22

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C H A P T E R   22
Electromagnetic Induction
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Chapter 22Electromagnetic Induction

• Induced emf and Induced current
• Motional emf
• Magnetic flux
• Faradays law of electromagnetic induction
• Lenzs law
• Applications cruise control, ground fault
  interrupter, induction stove, electric guitar,
  microphone, speaker.
• Electric generator
• Inductance
• Transformers and electric power transmission

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22.6 Applications of Electromagnetic Induction
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The Magnetic Playback Head of a Tape Deck
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A Moving Coil Microphone.
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22.7 The Electric Generator
Electric generators such as these supply
electrical power by producing an induced emf
according to Faraday's law of electromagnetic
induction.
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Electric Generator
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Emf of the Generator
The induced emf is given by the following
equation where, N is the number of turns in the
coil, B is the magnetic field, A is the area of
the coil, and ? is the angular velocity of the
rotation of the coil.
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Self-inductance (L)
The alternating current in the coil generates an
alternating magnetic field that induces an emf in
the coil. The effect in which a changing current
in a circuit induces an emf in the same circuit
is referred to as self-induction.
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Unit of Inductance
The inductance, L is measured in henries. The
magnitude of L depends on the geometry of the
coil and on the core material. By wrapping the
coil around a ferromagnetic (iron) core, the
magnetic flux and therefore the inductance can be
increased substantially relative to that for an
air core. Because of their self-inductance,
coils are known as inductors and are widely used
in electronics. Inductors come in all sizes,
typically in the range between millihenries and
microhenries.
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22.9 Transformers
A transformer is a device for increasing or
decreasing an ac voltage.
A transformer consists of a primary coil and a
secondary coil, both wound on an iron core. The
changing magnetic flux produced by the current in
the primary coil induces an emf in the secondary
coil. At the far right is the symbol for a
transformer.
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Power Transmission
Transformers play a key role in the transmission
of electric power.
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Transformer
A transformer consists of two coils, a primary
and a secondary, wound around a soft iron core
The two coils are linked by the magnetic field.
The soft iron core will provide a medium by
which the magnetic flux from the primary coil is
transferred to the secondary coil. Transformers
are designed so that nearly all the magnetic flux
from the primary coil is transferred to the
secondary coil.
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Transformer Equations
Using Faradays law we can write expressions for
the primary and secondary voltages as follows.
Dividing the above equations we get,
Assuming that there is no power loss, we can
write,
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Power Loss in Transmission Lines