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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
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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
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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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-- field theory--
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Lenzs Law The induced current opposes the
change of magnetic flux.
(if a conductor is present)
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Applications of electromagnetic induction ?
self-inductance in an AC circuit
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-- field theory--
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Applications of electromagnetic induction ? the
electric generator
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-- 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
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-- 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.
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Applications of electromagnetic induction ? the
transformer
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-- 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