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Electromagnetism

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8/5/08 Lecture 2 Part 1 Electromagnetism Part 1 : Electromagnetic induction; Faraday s Law Part 2 : Electromagnetic waves ... – PowerPoint PPT presentation

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Title: Electromagnetism


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Electromagnetism
????
Part 1 Electromagnetic induction
Faradays Law Part 2 Electromagnetic waves
?? ??
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Introduction Electricity E(x,t) and magnetism
B(x,t)
But also, the E and B fields affect each
other electricity and magnetism go together to
make a unified interaction ?? electromagnetism
4
?? ??
The discovery of electromagnetic induction
Electromagnetic induction was discovered
independently by Michael Faraday (London) and
Joseph Henry (Albany, NY) in 1831.
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Simplest demonstration of electromagnetic
induction
Observation when the magnet moves, a current
occurs in the coil of wire (measured by the
galvanometer).
Faraday developed many experiments to produce the
effect, in different ways. Changing the magnetic
field induces electric current in a nearby
conductor.
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But the electric current is a secondary
effect. The primary effect is an electric
field.Electromagnetic induction is a field
effect.
When the magnetic field changes in time, there is
an induced electric field.
(If a conductor is present, then current is
driven by the induced electric field.)
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Electromagnetic induction is a field effect.
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Faradays Law and Field Theory
?? ??
-- field theory--
??? ????
Advanced Calculus!!
Lenzs Law The induced current opposes the
change of magnetic flux.
(if a conductor is present)
9
Applications of electromagnetic induction ?
self-inductance in an AC circuit
?? ??
-- field theory--
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Applications of electromagnetic induction ? the
electric generator
?? ???
-- electric generator --
The design principle how it works
As the coil rotates, the flux F alternates, which
induces an alternating emf around the coil.
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?? ???
The electric generator the practical device
-- electric generator --
Torque must be applied to turn the rotating coil.
Mechanical work is converted to electrical energy.
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Applications of electromagnetic induction ? the
transformer
???
-- transformer --
Primary Coil
Secondary Coil
Iron Core
(1)
(2)
(3)
(1) Alternating flux is created here (2) which
makes an alternating flux here (3) which makes
and alternating emf here.
14
Applications of electromagnetic induction ? the
transformer
???
-- transformer --
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Water flow drives the turbine
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  • Alternative Energy Sources ?
  • renewable
  • safe for the environment
  • no carbon dioxide emission
  • less expensive

???? ????
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?? ???
The electric generator the practical device
-- electric generator --
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Gangwon Wind Park in Korea
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Photovoltaic Solar Cells
  • direct conversion from sunlight to electricity
  • there is no mechanical generator
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