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## Electromagnetic Induction

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### Electromagnetic Induction Created for CVCA Physics By Dick Heckathorn 21 April 2K + 5 Purpose for Chapter 19 To investigate how one can generate electrical energy ... – PowerPoint PPT presentation

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Title: Electromagnetic Induction

1
ElectromagneticInduction
• Created for CVCA Physics
• By
• Dick Heckathorn
• 21 April 2K 5

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

6
• Question?
• Can a magnetic field cause electrons to move?

7
Demonstration 1
• Move a wire
• through the jaws
• of a
• horseshoe magnet.
• Results?

Large magnet wire Galvanometer
8
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
9
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.

10
Demonstration 2
• Plunge
• a bar magnet
• into and out of
• the core of a coil.

Bar magnet coil wire Galvanometer
11
Demonstration 2
FMech
I
B
Magnets field has direction of
Direction of blue arrows
Or coil moves to right
Due to mechanical force to right
Thus induced current is in direction.
B field of magnet at bottom of coil is in what
direction?
Magnet plunge into the coil.
12
Demonstration 2
FMech
I
B
Magnets field has direction of
Thus induced current is in direction.
Magnet pulled out of the coil.
B field of magnet at bottom of coil is what
direction?
Direction of blue arrows
Or coil moves to left
Due to mechanical force to left
13
Direction of the Magnetic Field relative to right
side of coil is
Direction of the mechanical force on wire is
B
I
FM
Direction of the Induced Current is
14
Direction of the Magnetic Field relative to right
side of coil is
Direction of the mechanical force on wire is
B
I
FM
Direction of the Induced Current is
15
Direction of the Magnetic Field relative to right
side of coil is
Direction of the mechanical force on wire is
none
B
Direction of the Induced Current is there is
none
16
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.

17
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
18
Demonstration 3
• Open the switch.

What happens to the meter?
Green or large power source iron ring or my
coils - wire Galvanometer
19
Conclusion
• There is an induced current
• only
• when the
• magnetic field
• is changing
• in the iron ring.

20
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)

21
Demonstration 3
I
?B
I
Results ?
Close Switch
Induced
22
Demonstration 3
I
?B
I
Results ?
Open Switch
Induced
23
19.3 Magnitude of Induced Electric Potential 738
24
Ohms Law Says
25
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
26
Lenz Reasoned
• The induced current
• sets up an
• induced magnet field.
• This induced field
• interacts with
• inducing field of the magnet.

27
How do they interact?
• Either one or the other.

28
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
29
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
30
Conclusion

31
Conclusion
• An induced current
• flows in such a direction
• that the created
• induced field
• opposes the action of
• the inducing field.

32
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
33
What is the pole of magnet?
S
S
• Left end of coil must be

S
Why?
Right hand grasping coil correctly.
Right pole of bar magnet must
oppose South pole of coil
therefore it must be
S
34
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
35
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
36
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)
37
Polarity of Coil? Direction I ?
S
• R-end of coil must be

S
Why?
Must oppose N-pole of magnet.
Current in coil must be in direction (in wire
near us)
38
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

39
AC Generator
• Look at segment X-W

B
I
F
Force in direction?
Induced current in direction?
B in direction?
40
AC Generator
• Look at segment X-W ½ turn later

B
F
Force in direction?
Induced current in direction?
B in direction?
41
AC Generator Summary
I
I
42
AC Current vs Time
43
DC Generator
• Look at segment X-W

B
I
F
Induced current in direction?
Force in direction?
B in direction?
44
DC Generator
• Look at segment X-W ½ turn later

B
F
I
Force in direction?
Induced current in direction?
B in direction?
45
DC Generator - Summary
I
I
46
Maximizing Output
• Increase turns on coil
• Winding coil on soft iron core
• Increase speed of rotation
• Increase strength of B-field

47
19.6 The Transformer
• All large scale
• electrical generating
• systems
• generate electricity
• using
• AC generators.

48
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.
49
of Electrical Power Wasted
• 480-kW Power transmitted
• 10-ohm Resistance
• 12-kV Electric Potential

P I2 . R 16 kW 3.33 loss
50
of Electrical Power Wasted
• 480-kW Power transmitted
• 10-ohm Resistance
• 240-kV Electric Potential

P I2 . R 40 W 0.0083 loss
51
The Transformer
• changes the
• electric potential difference (V)
• by varying
• number of windings
• of two different coils
• around a common
• soft iron core.

52
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.

53
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.

54
Conclusion
• If power source is connected
• to the coil with the
• smaller number of turns,
• the output current
• is less than the input current.

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

56
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.

57
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
58
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

59
Demo - Coil
• 1. Used as Magnetizer
• 2. Two Rings Adjust Height
• Induced Voltage
• Various Size Coils
• Bulb connected to coils

60
Demo - Coil
1. Magnetic Braking
2. Dropping Magnet
3. Dropping Copper Tube
4. Ball Magnet

61
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Thats all folks!
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71
AC Generator Direction of I?
72
AC Generator Direction of I?
73
AC Generator Direction of I?
74
AC Generator Direction of I?
75
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
76
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