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8/5/08
Lecture 2 Part 1
1
Electromagnetism
전자기학
Part 1 : Electromagnetic induction;
Faraday’s Law
전자 유도
Part 2 : Electromagnetic waves
전자기파
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Lecture 2 Part 1
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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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Lecture 2 Part 1
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전자 유도
The discovery of electromagnetic induction
Electromagnetic induction was discovered
independently by Michael Faraday (London) and
Joseph Henry (Albany, NY) in 1831.
1797 –1878
Faraday
1791 -1867
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Lecture 2 Part 1
Henry
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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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Faraday’s Law and Field Theory
장의 이론
-- field theory--
d
emf  
dt
B
E  
t
Advanced Calculus!!
진보된 미적분학
Lenz’s 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
장의 이론
-- field theory--
R  V /I
L   / I  flux/curre nt
emf  L dI / dt
dI
V (t)  L
 RI (t)
dt
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Applications of electromagnetic induction
► the electric generator
전기 발전기
-- electric generator --
The design principle — how it works
As the coil rotates, the flux  alternates, which
induces an alternating emf around the coil.
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The electric generator
— the practical device
전기 발전기
-- electric generator --
Torque must be applied
to turn the rotating coil.
Mechanical work is
converted to electrical
energy.
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Appliances
120 volts @ 60
hertz
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Transformers
Mutual
inductance, i.e.,
electromagnetic
induction
Transmission
Lines
345,000 volts
(AC)
Lecture 2 Part 1
Power Plant
Electric generators
are driven by a
primary energy
source; e.g.,
•Coal furnace
•Nuclear reactor
•Hydroelectric dam
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Applications of electromagnetic induction
► the transformer
변압기
-- transformer --
Primary Coil
(1)
Secondary Coil
(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
변압기
-- transformer --
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electromagnetic
induction
Water flow
drives
8/5/08the
turbine
Percent used for
Primary Energy Sources
electric power in USA
Coal……………………………………… 50 %
Petroleum or Natural Gas……… 10 %
Nuclear Reactor…………………… 20%
Hydroelectric………………………… 20%
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Alternative Energy Sources ?
• renewable
• safe for the environment
• no carbon dioxide emission
• less expensive
양자택일 에너지원
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The electric generator
… the practical device
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Lecture 2 Part 1
전기 발전기
-- 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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