Electromagnetism

1
Electromagnetism
Michael Faraday

• Physics 100
• Chapt 15

2
General circuit
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Appliance
-

I

-
Energy source (device that separates - charge)
3
Moving a Conductor in a B-fieldseparates -
charges
I
4
Use this to drive an electric circuit




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5
Moving wire loop in a B field
v


An electric current is induced in the loop
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Either the magnet or the loop can move
v


an electric current is induced in the loop
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Magnetic flux (F) thru a loop
F BA-
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Flux thru a coil of N loops
F N BA-
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Faradays law
Michael Faraday
change in F elapsed time
Induced voltage in a circuit
change in N BA- elapsed time
EMF
Electro-Motive Force
10
Rotating coil in B field
B
A- 0 ? F 0
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Rotating coil in B field
B
A- Acoil ? F maximum
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Rotating coil in B field
B
A- 0 (again) ? F 0
13
AC voltage
14
Lenz Law
B
B
S
B-field from induced current


B-field from induced current
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N
v
v
the fall produces an induced current
the B-field produced by the induced current tries
to impede the fall
15
Lenz law

• An induced voltage always gives rise to an
  electric current that creates a magnetic field
  that opposes the influence that produced it.

16
Maglev trains
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Maglev