8/5/08 Lecture 2 Part 1 1

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Nov 16, 2013 (3 years and 11 months ago)

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8/5/08

Lecture 2 Part 1

1

8/5/08

Lecture 2 Part 1

2

Electromagnetism

전자기학

Part 1 : Electromagnetic induction;



Faraday’s Law


Part 2 : Electromagnetic waves

전자

유도

전자기파

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Lecture 2 Part 1

3

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.

전자

유도

1791
-
1867

Faraday

1797

1878

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

dt
d
emf



t






B
E
Advanced Calculus!!

진보된

미적분학


Lenz’s Law: The induced current* opposes the
change of magnetic flux.

(*if a conductor is present)

--

field theory
--

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장의

이론

)
(
)
(
/
nt
flux/curre


/
/
t
R
dt
d
L
t
V
dt
d
L
emf
L
V
R
I
I
I
I
I








--

field theory
--

Applications of electromagnetic induction



self
-
inductance in an AC circuit

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Applications of electromagnetic induction



the electric generator

The
design
principle



how it works

전기

발전기


--

electric generator
--

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

Transformers

Mutual
inductance, i.e.,
electromagnetic
induction

Transmission
Lines

345,000 volts
(AC)

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
--

(1) Alternating flux is created here …

(2) which makes an alternating flux here …

(3) which makes and alternating emf here.

Primary Coil

Secondary Coil

(1)

(2)

(3)

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변압기


--

transformer
--

Applications of electromagnetic induction



the transformer

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electromagnetic

induction

Water flow
drives the
turbine

Coal………………………………………

Petroleum or Natural Gas………

Nuclear Reactor……………………

Hydroelectric…………………………

Percent used for

electric power in USA

50 %

10 %

20%

20%

Primary Energy Sources

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Alternative Energy Sources ?




renewable



safe for the environment



no carbon dioxide emission



less expensive

양자택일

에너지원


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17

전기

발전기


--

electric generator
--

The electric generator

… the practical device

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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