electromagnetic induction faradaylenz. why does electromagnetic induction occur? horizontal magnetic...
DESCRIPTION
Faraday’s Law Magnetic Flux Density, B Area, A Flux, = B x A Unit of Flux is the Weber (Wb) Flux is a vector term Flux linkage of a coil = N x = N x B x A Coil with N turnsTRANSCRIPT
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Electromagnetic Induction
Faraday Lenz
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Why does Electromagnetic Induction Occur?
Horizontal Magnetic Field
Move wire down
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I
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+
I
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Faraday’s Law
Magnetic Flux Density, B
Area, A
Flux, = B x A
Unit of Flux is the Weber (Wb)Flux is a vector term
Flux linkage of a coil = N x = N x B x A
Coil with N turns
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Faraday’s Law• If you make a wire cut through magnetic flux then
an emf will be induced.• Faraday’s Law:
– The magnitude of the induced emf is equal to the rate of change of flux linkage
• This effect can be made by moving the magnetic field or moving the conductor
tN
tN
(s) Taken, Time
(weber) Linkage,Flux in Change(volts) emf, Induced
= gradient of the graph of Flux Linkage against Time
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Whiteboard Challenge• On your whiteboard,
draw the axes as shown• Now sketch the shape of
the top graph as the car goes through the loop
• Now sketch the shape of the bottom graph, remembering that this graph is showing the gradient of the first graph.
N
t
t
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tN
tN
(s) Taken, Time
(weber) Linkage,Flux in Change(volts) emf, Induced
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8
Time/s
emf/V
-0.001
0
0.001
0.002
0.003
0.004
0.005
0.006
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8
Time/s
F
lux
Link
age
/
Flux linkage
Rate of change of Flux linkage
This is the gradient of this
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N
S
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Now for you to get on with some work!
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Questions:
• Page 241, Q4-8 • Extension: Question 10
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Lenz’s Law• Do we need to apply Lenz’s law?
– Does moving wire, a moving magnet or a changing strength magnet mean the flux lines are being cut?
• Yes: Then an emf will be induced in the wire.
– Is the wire part of a complete circuit?• Yes: Then a current will flow through the wire
– Lenz’s law states that the direction of the induced current will produce a magnetic field to oppose the motion.
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Lenz’s Law• Magnet moves towards the coil• Flux lines from the magnet are being cut by the coil• Faraday’s Law states that: An emf will be induced in the coil• The coil makes a circuit so there will be a current in the coil• Lenz’s Law states that: The Left hand end of the coil will
have an induced N pole to oppose the motion• Right-hand grip rule indicates that the current must flow down
at the back of the coil and up at the front.
S N N S
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Now some tough questions…
• Page 278, questions 20 & 21• … and if you want a real challenge (yes I
know that you do!) have a go at 22 as well
Note: You can also use the Right Hand Grip rule to show the direction of flux inside a solenoid (from South to North), if your fingers indicate the direction of current
Q22