Download Motional EMF

Motional EMF
Motional emf
• e = BLv
– B: magnetic field (T)
– L: length of bar moving through field
– v: speed of bar moving through field.
• Bar must be “cutting through” field lines. It
cannot be moving parallel to the field.
• This formula is easily derivable from Faraday’s
Law of Induction
Motional emf - derivation
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e = DFB/Dt
e = D(BA) /Dt (assume cosq = 1)
e = D(BLx) /Dt
e = BLDx /Dt
e = BLv
Sample Problem
• How much current flows through the resistor?
How much power is dissipated by the resistor?
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B = 0.15
T
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v = 2m/s
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Sample Problem
• In which direction is the induced current through
the resistor (up or down)?
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B = 0.15
T
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v = 2m/s
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Sample Problem
• Assume the rod is being pulled so that it is traveling at a
constant 2 m/s. How much force must be applied to keep
it moving at this constant speed?
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W
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50
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B = 0.15
T
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v = 2m/s
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Lab: Magnetic Field Map
Using a compass, map the magnetic
field inside and outside your
solenoid. Do the following:
a) Put together 4 sheets of graph
paper. Write all group members’
names on paper.
b) Trace the solenoid (true size)
I
c) Draw the Compass Rose
d) Connect to DC outlet
e) Map magnetic field lines with
compass
f) Draw North and South Poles of
solenoid
g) Extend field lines through solenoid.