Electromagnetism - The Burns Home Page

03/12/2010
Electromagnetism Review
N
t
Faraday’s Law Practice Question
Electromagnetism Review
B Direction
Lenz’s Law
You have a coil of wire with 30 loops, each of which has
an area of 2.0 x 10 -3 m 2 . The Magnetic Field B is
perpendicular to the surface. At time t=0 s, the Field B is
measured at 1.0 T. At time, t=.2 s, the Field B is measured
at 1.1 T. What is the average emf inside the coils.
Lenz’s Law describes the direction of
the Electric Current produced by a
changing Magnetic Field.
N
t
BAcos
N
t
0.03V
B BAcos
1.1 1.0 2.0 10 3 2
T T m cos 0
30
0.2s
0.0s
The Thumb points in the direction of
the Current. The fingers curl in the
direction of the Magnetic Field.
Electromagnetism Review
Lenz’s Law
Electromagnetism Review
Lenz’s Law
B Direction
Change in Flux
An influenced emf gives rise to a
Electric Current whose Magnetic Field
opposes the original change in Flux.
The Right Hand Rule can aid us in
these situations.
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
X X X X X X X
Notice how the area is lessened when the loop is stretched.
Since the Flux is reduced, the Electric Current flows in the
direction that would produce the B field. This direction tries
to help maintain the original Flux.
The induced current attempts to maintain the status quo.
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