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Electromagnetic Induction

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Electromagnetic Induction Created for CVCA Physics By Dick Heckathorn 3 May 2K+4 Purpose for Chapter 19 To investigate how one can generate electrical energy ... – PowerPoint PPT presentation

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Title: Electromagnetic Induction

1
Electromagnetic Induction
• Created for CVCA Physics
• By
• Dick Heckathorn
• 3 May 2K4

2
What physics principles does this picture
illustrate?
3
Purpose for Chapter 19
• To investigate how one can generate electrical
energy (electricity)
• 2. Techniques for distribution

4
19.1 Electromagnetic Age 738
• Voltaic Cell
• Only known source of continuous electric potential

5
• Question?
• Can a magnetic field cause electrons to move?

6
Demonstration 1
• Move a wire
• through the jaws
• of a
• horseshoe magnet.
• Results?

Large magnet wire Galvanometer
7
A Mechanical Force is
but in the opposite direction.
to the mechanical force
that is equal in magnitude
exerted on a wire in a B field.
This induced current in a B field
gives rise to a magnetic force
An induced current is produced.
N
FMag
FMech
IInd
B
8
Demonstration 1
• Electrons only flowed
• when the conductor was moving through the
magnetic field.
• They were moving in a direction opposite to the
induced current as the induced current was the
movement of positive charges.

9
Demonstration 2
• Plunge
• a bar magnet
• into and out of
• the core of a coil.

Bar magnet coil wire Galvanometer
10
Demonstration 2
FMech
I
B
Or coil moves to right
Magnets field has direction of
Direction of blue arrows
B field of magnet at bottom of coil is what
direction?
Magnet plunge into the coil.
Due to mechanical force to right
Thus induced current is in direction.
11
Demonstration 2
FMech
I
B
Thus induced current is in direction.
Magnets field has direction of
Due to mechanical force to left
B field of magnet at bottom of coil is what
direction?
Or coil moves to left
Magnet pulled out of the coil.
Direction of blue arrows
12
Direction of the Induced Current is
B
I
FM
B
I
FM
B
FM
None
13
Conclusion
• Charges flow only when
• the bar magnet is moving
• into or out of the coil
• or
• when the coil moves
• relative to the magnet.

14
Demonstration 3
• Close the switch.

What happens to the meter?
The two wires are not connected.
Anything surprising?
Green or large power source iron ring or my
coils - wire Galvanometer
15
Demonstration 3
• Open the switch.

What happens to the meter?
Green or large power source iron ring or my
coils - wire Galvanometer
16
Conclusion
• There is an induced current
• only
• when the
• magnetic field
• is changing
• in the iron ring.

17
Factors affecting magnitude of induced current
1. Number of turns of wire in the coil
2. Strength of magnetic
• field of the magnet
• 3. Rate at which magnetic field changes relative
to wire (relative speed)

18
Demonstration 3
I
?B
I
Results ?
Close Switch
Induced
19
Demonstration 3
I
?B
I
Results ?
Open Switch
Induced
20
19.3 Magnitude of Induced Electric Potential 738
21
Ohms Law Says
22
19.4 Direction of Induced Current Lenzs Law 741
• Know so far?
• S-Pole enters coil
• Current in one direction
• S-Pole removed from coil
• Current in opposite direction

Know so far? S-Pole enters coil Induced current
is in a direction opposite that when N-Pole was
involved
23
Lenz Reasoned
• The induced current
• sets up an
• induced magnet field.
• This induced field
• interacts with
• inducing field of the magnet.

24
How do they interact?
• Either one or the other.

25
Lets assume
S
• The current would produce

an induced magnetic field in coil
R-hand rule says right end is
S
of bar magnet pulling them together.
S-pole would
attract the N-Pole
Impossible
Why?
Lenz reasoned
26
Lets look at other option
N
• The current would produce

an induced magnetic field in coil
R-hand rule says right end is
N
N-pole coil opposes N-pole magnet
Must do work to bring them together
27
Conclusion

28
Conclusion
• An induced current
• flows in such a direction
• that the created
• induced field
• opposes the action of
• the inducing field.

29
What is direction of Iinduced?
• Lower end of coil must be

N
Why?
Coil must oppose removal of S-pole
N
R-hand rules says current flows
across front of the coil.
to left
30
What is the pole of magnet?
S
S
• Left end of coil must be

S
Why?
Pole of bar magnet must
oppose
S-pole of coil
Must be
S
31
Polarity of Coil? Direction I ?
• Top of coil must be

N
Why?
Must oppose N-pole of magnet.
N
Current in coil must be (in wire near us)
in direction
32
Polarity of Coil? Direction I ?
• Bottom of coil must be

S
Why?
Must oppose S-pole of magnet.
S
Current in coil must be (in wire near us)
in direction
33
Polarity of Coil? Direction I ?
N
• R-end of coil must be

N
Why?
Must oppose S-pole of magnet.
Current in coil must be in direction (in wire
near us)
34
Polarity of Coil? Direction I ?
S
• R-end of coil must be

S
Why?
Must oppose S-pole of magnet.
Current in coil must be in direction (in wire
near us)
35
19.5 Electrical Generators AC and DC 745
• Ready to produce a device
• capable of producing
• a continuous electric current
• and electric potential difference
• by electromagnetic induction

36
AC Generator
• Look at segment X-W ½ turn later

B
F
I
Force in direction?
Induced current in direction?
B in direction?
37
AC Generator
• Look at segment X-W

B
I
F
Force in direction?
Induced current in direction?
B in direction?
38
AC Generator
I
I
39
AC Current vs Time
40
AC Current vs Time
41
AC Generator Direction of I?
42
AC Generator Direction of I?
43
AC Generator Direction of I?
44
AC Generator Direction of I?
45
DC Generator
• Look at segment X-W

B
F
I
Induced current in direction?
Force in direction?
B in direction?
46
DC Generator
• Look at segment X-W ½ turn later

B
F
I
Force in direction?
Induced current in direction?
B in direction?
47
DC Generator
I
I
48
Maximizing Output
• Increase turns on coil
• Winding coil on soft iron core
• Increase speed of rotation
• Increase strength of B-field

49
19.6 The Transformer
• All large scale
• electrical generating
• systems
• generate electricity
• using
• AC generators.

50
Energy Transmission
2400 V
240 V
12,000 V
240,000 V
The voltage must then be reduced to a value that
is acceptable for home usage.
The voltage is increased to reduce the energy
lost as it is transferred through the wires over
a long distance.
51
of Electrical Power Wasted
• 10-kW Power transmitted
• 1-ohm Resistance
• 200-V Electric Potential

P I2 . R 2.5 kW 25 loss
52
of Electrical Power Wasted
• 10-kW Power transmitted
• 1-ohm Resistance
• 2000-V Electric Potential

P I2 . R 25 W 0.25 loss
53
Demonstration
• Measure the potential difference
• of a coil within a coil.
• Have one coil connected to one coil and then the
other as the measurements are made.
• First with DC and then AC
• Electrical Potential (Voltage)

Green Power Source - Double coil apparatus 2
voltmeters
54
The Transformer
• changes the
• electric potential difference (V)
• by varying
• number of windings
• of two different coils
• around a common
• soft iron core.

55
Conclusion
• If power source is connected
• to the coil with the
• smaller number of turns,
• the output potential difference
• is greater than the input potential difference.

56
Conclusion
• If power source is connected
• to the coil with greater
• number of turns,
• the output potential difference
• is less than the input potential difference.

57
Demonstration
• Measure the current
• of a coil within a coil.
• Have one coil connected to one coil and then the
other as the measurements are made.

Green Power Source - Double coil apparatus 4
multimeters
58
Conclusion
• If power source is connected
• to the coil with the
• smaller number of turns,
• the output current
• is less than the input current.

59
Conclusion
• If power source is connected
• to the coil with greater
• number of turns,
• the output current
• is greater than the input current.

60
Question
• How does the output power compare to the input
power?
• Did Poutput Pinput ?
• If so, there is a
• Conservation of Energy as the potential
difference is changed.

61
Demonstration
• Investigate the construction of a dissectible
transformer.

Repeat the potential difference and current
measurements as done with coil within a coil.
Green Power Source Dissectible transformer 2
multimeters
62
Designing Transformers
• Copper coils have low R
• to reduce power loss
• Core High Permeability
• to reduce energy to ?B in core
• Cores Shape
• to maximize induction

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Thats all folks!
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