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Induced Voltage
Changing magnetic fields can create a potential
difference (and thus cause current flow) in a
conductor.
This is the principle behind generators, transformers,
induction coils, and magnetic levitation
(superconductors, trains).
Electromagnetic Induction
A motor uses a magnetic field to convert electrical
energy to mechanical energy.
The reverse can also be done. Devices that
convert mechanical energy to electrical energy are
called generators.
A wire moving perpendicular to a magnetic field will
experience an induced voltage, and thus a current.
The wire must cut across field lines, so the more field
lines, the more current.
We can calculate the induced voltage by using:
V = Bl v
V = induced potential difference
B = magnetic flux
l = length of the wire
v = speed of the wire
Practice Problem:
Calculate the potential difference induced in a wire
0.20 m long and moved 8.0 m/s through a 4.0x10 -1 T
magnetic field.
l = 0.20 m
v = 8.0m/s
V=Bv
B = 4.0 x 10 -1 T
l
V = (4.0 x 10 -1 T)(0.20m)(8.0m/s)
V = 0.64 V
Induced potential difference is also known as
electromotive force (emf). Only a change in
magnetic field is necessary - not actual motion.
So a changing magnetic field will also cause an
induced voltage.
Generators
A device that converts mechanical energy (falling
water, steam, hand crank, etc) into electrical energy.
To make a simple generator, wrap a coil of wire
around and iron core, place it in a magnetic field, and
rotate.
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When the coil is perpendicular to the field lines,
current is high. When the coil is parallel, the current
is zero. When it is in between, the current is in
between.
This is AC - alternating current
Find the direction of current flow:
X
X
X
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X
Find the direction of current flow:
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F
Find direction of induced current flow:
N
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Wire is
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Find the field:
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X
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F X
X
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X
Find the direction of induced current:
X
X
X
X
X
X v
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X
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X
X
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