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Magnetism

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Tomorrow: Magnetism Quiz and notebookcheck A voltage will be induced in a wire loop when the magnetic field within that loop changes. aligns with the electric ... – PowerPoint PPT presentation

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Title: Magnetism


1
Magnetism
2
  • What comes to mind when you see this picture?
  • 2. What do you think causes this?

3
  • What causes auroes interactions between the
    solar flares and a magnetic field.
  • Do auroras occur only on Earth?
  • Where is what you need
  • 1. Solar flares - charged particles and energy to
    interact with a planets magnetic field
  • 2. A planetary magnetic field (probably of some
    strength) that traps electrons from space
  • 3. A planetary atmosphere that contains ionic
    gases that interact with energetic electrons from
    the magnetic field and produce light through
    excitation and relaxation of their electrons

4
So, with these conditions, we have observed
auroras on Jupiter and Saturn. Both planets have
powerful magnetic fields and atmospheres with
ionized gases, mainly hydrogen and helium. The
Hubble Space Telescope caught images of auroras
on Jupiter, and the Cassini probe orbiting Saturn
has photographed auroras there.
5
What is Magnetism?
  • Magnetism is the attraction of a magnet to
    another object.

6
What are the magnetic properties of the Earth?
  • The Earth has an immense magnetic field around it
    called the magnetosphere.

7
36.6 Magnetic Forces on Moving Charged Particles
The deflection of charged particles by magnetic
fields provides a TV picture. Charged particles
from outer space are deflected by Earths
magnetic field, which reduces the intensity of
cosmic radiation. A much greater reduction in
intensity results from the absorption of cosmic
rays in the atmosphere.
What would happen if we had no magnetic field?
8
36.2 Magnetic Fields
Iron filings sprinkled on a sheet of paper over a
bar magnet will tend to trace out a pattern of
lines that surround the magnet. magnetic field
-The space around a magnet, in which a magnetic
force is exerted The shape of the field is
revealed by magnetic field lines.
9
What are Magnetic Poles?
  • Magnets have two ends, called magnetic poles.
  • Magnetism is strongest at the poles of a magnet.

10
Magnetic Poles
  • Magnetic poles that are alike repel each other.
  • North repels North
  • South repels South
  • Poles that are not alike attract each other
  • North attracts South
  • South attracts North

11
What is a Magnetic Field?
  • The magnetic force exerted in the region around
    the magnet is the magnetic field.
  • This allows magnets to interact without touching.

12
What are Magnetic Field Lines?
  • Magnetic Field Lines spread out from one pole,
    curve around the magnet, and return to the other
    pole.

13
  1. What happens if you break a magnet in half?

S
N
14
36.1 Magnetic Poles
If you break a bar magnet in half, each half
still behaves as a complete magnet. Break the
pieces in half again, and you have four complete
magnets. Even when your piece is one atom thick,
there are two poles. This suggests that atoms
themselves are magnets.
15
What do atoms have to do with it?
  • All atoms have magnetic fields because of the
    charged particles inside.
  • Most atoms magnetic fields point in random
    directions, so they all cancel each other out.

16
What do atoms have to do with it?
  • In magnetized material, all or most of the
    magnetic fields are arranged in the same
    direction.
  • A material that keeps its magnetism is called a
    permanent magnet.

17
36.3 The Nature of a Magnetic Field
Most substances are not magnets because the
various fields cancel one another due to
electrons spinning in opposite directions. In
materials such as iron, nickel, and cobalt,
however, the fields do not cancel one another
entirely. An iron atom has four electrons whose
spin magnetism is not canceled. Each iron atom,
then, is a tiny magnet. The same is true to a
lesser degree for the atoms of nickel and cobalt.
18
36.3 The Nature of a Magnetic Field
  • Spin Magnetism
  • Every spinning electron is a tiny magnet.
  • A pair of electrons spinning in the same
    direction makes up a stronger magnet.
  • Electrons spinning in opposite directions work
    against one another.
  • Their magnetic fields cancel.

19
36.4 Magnetic Domains
  • The magnetic fields of individual iron atoms are
    strong.
  • Interactions among adjacent iron atoms cause
    large clusters of them to line up with one
    another.
  • magnetic domains clusters of aligned atoms
  • Each domain is perfectly magnetized, and is made
    up of billions of aligned atoms.
  • The domains are microscopic, and there are many
    of them in a crystal of iron.

20
  • Magnetic resonance imaging

21
  • 1. What are magnets used for?
  • 2. Why does a magnet lose its power when heated
    or dropped?

22
  • 1. What are magnets used for?
  • 2. Why does a magnet lose its power when heated
    or dropped?
  • http//videos.howstuffworks.com/science-channel/29
    143-100-greatest-discoveries-earths-magnetic-field
    -video.htm

23
  • 1. How do these birds know where to go?
  • 2. What invention helped humans navigate the
    world?
  • 3. What causes magnetism?

24
What is going to happen to magnetic fields?
  • Video earths magnetic field
  • Take notes and summarize
  • http//videos.howstuffworks.com/science-channel/29
    143-100-greatest-discoveries-earths-magnetic-field
    -video.htm

How would the earth be affected if there were no
magnetic fields?
25
36.9 Earths Magnetic Field
More than 20 reversals have taken place in the
past 5 million years. The most recent occurred
780,000 years ago. We cannot predict when the
next reversal will occur because the reversal
sequence is not regular. Recent measurements
show a decrease of over 5 of Earths magnetic
field strength in the last 100 years. If this
change is maintained, there may be another field
reversal within 2000 years. Compass lab
26
36.9 Earths Magnetic Field
Currents in the molten part of Earth beneath the
crust provide a better explanation for Earths
magnetic field. Most geologists think that
moving charges looping around within Earth create
its magnetic field. Another possible cause for
Earths magnetic field is convection currents
from the rising heat of Earths core. Perhaps
such convection currents combined with the
rotational effects of Earth produce Earths
magnetic field.
Extra credit research What gives the Earth its
magnetic force?
27
Figure 22-6
28
36.4 Magnetic Domains
The arrows represent domains, where the head is a
north pole and the tail a south pole. Poles of
neighboring domains neutralize one anothers
effects, except at the ends.
29
  • Compass magnetized metal on a frictionless
    bearing (water) that lines up with the earths
    magnetic field.
  • Questions to consider for reasoning
  • How do you know that your needle was a compass?
  • What is the point of a frictionless bearing?

30
  • Questions to consider for reasoning
  • How do you know that your needle was a compass?
  • What is the point of a frictionless bearing?
  • Bonus
  • If you stroke the needle with the north end of a
    magnet which direction would they point and why?
  • Where would your compass work better?

31
  • http//en.wikipedia.org/wiki/Orders_of_magnitude_(
    magnetic_field)

Magnetic strength (tesla)
Human brain 10-12
Earth 31-60 10-5
Refrigerator magnet 10-3
Speaker 1
MRI 7
Strongest human created 100
Magnetar 109
32
  • Why did you have to expose the needle to a
    magnetic field to make it a compass?
  • If you stroke the needle with the north end of a
    magnet which direction would they point and why?

33
  • The needle rotated until it found the magnetic
    field of the earth. The water helped rotate the
    needle (by providing low friction). The needle
    was magnetic because when placed in the styrofoam
    the needle still pointed north, no matter which
    direction the dish was rotated. The needle
    became a compass because it pointed to magnetic
    north. The earth attracted the magnetic domains
    of the needle with its magnetic field. KP

34
36.5 Electric Currents and Magnetic Fields
  • Iron filings sprinkled on paper reveal the
    magnetic field configurations about
  • a current-carrying wire
  • a current-carrying loop
  • a coil of loops

35
  • What does electric current have to do with
    magnetism?

36
What do Electric Currents have to do with Magnets?
  • An electric current produces a magnetic field.
  • The direction of the current determines the
    direction of the magnetic field.

37
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38
What is an Electromagnet
  • An Electromagnet is a strong magnet that can be
    turned on and off.
  • Electromagnet consists of a current-carrying
    wire wrapped around an iron core.

39
Exit slip
  • What is a claim that you can make based on your
    experiment?
  • Evidence where you able to pick up the wire
  • Reasoning how does your electromagnet work

40
  • What does electricity have to do with magnetism?
  • What can we use electomagnets for?
  • What are two ways of increasing the strength of
    an electromagnet?

41
Characteristics of Electromagnets
  • Strength depends on the number of coils and the
    size of the iron core.
  • The greater the number of turns the coil has the
    stronger the magnet will be.
  • The closer the coils are the stronger the magnet
    will be.

42
36.5 Electric Currents and Magnetic Fields
A superconducting electromagnet can generate a
powerful magnetic field indefinitely without
using any power. At Fermilab near Chicago,
superconducting electromagnets guide high-energy
particles around the four-mile-circumference
accelerator. Superconducting magnets can also be
found in magnetic resonance imaging (MRI) devices
in hospitals.
43
Uses of elecromagnets
44
  • Electromagnetic induction electric current is
    produced by moving a magnet across a wire coil

45
37.1 Electromagnetic Induction
  • Work must be done to move the magnet.
  • Current induced in the loop produces a magnetic
    field (the imaginary yellow bar magnet), which
    repels the bar magnet.
  • When the bar magnet is pulled away, the induced
    current is in the opposite direction and a
    magnetic field attracts the bar magnet.

46
37.3 Generators and Alternating Current
47
37.3 Generators and Alternating Current
As the loop rotates, the magnitude and direction
of the induced voltage (and current) change. One
complete rotation of the loop produces one
complete cycle in voltage (and current).
48
Magnetic field direction
  • Magnetic fields are produced by moving electric
    charges
  • They go from south to north

49
  • Frequency number of cycles per second
  • SI unit is hertz
  • Wanna dougnut? out

50
Motors and Generators
  • Motor a device that changes electric current
    into mechanical energy.
  • Generator a device that changes mechanical
    energy into electrical current.

51
  • How many motors are in your mammas car? Can
    you name them?

52
37.2 Faradays Law
  • Faradays law states that the induced voltage in
    a coil is proportional to the product of the
    number of loops, the cross-sectional area of each
    loop, and the rate at which the magnetic field
    changes within those loops.
  • Induced voltage number of loops X area of loop
    / time

53
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54
  • http//phet.colorado.edu/en/simulation/faradays-la
    w
  • What is going to happen when the magnet is moved?

55
Question of the Day
  • Read the volume of the graduated cylinders,
    estimate the 10 ml read to the nearest
  • .01 ml
  • Estimate the 100 ml to the nearest .1 ml
  • How could we determine the uncertainty of the
    cylinders?

56
2/20
  • How is electricity produced?
  • What are three ways of increasing voltage output
    in a generator?

57
37.3 Generators and Alternating Current
The voltage induced by the generator alternates,
and the current produced is alternating current
(AC). The current changes magnitude and
direction periodically. The standard AC in North
America changes magnitude and direction during 60
complete cycles per second60 hertz.
58
  • Why is it important for people to understand
    induction?
  • Give an example of when you might use a
    generator?

59
37.3 Generators and Alternating Current
An energy source of some kind is required to
operate a generator. Some fraction of energy
from the source is converted to mechanical energy
to drive the turbine. The generator converts
most of this to electrical energy. Some people
think that electricity is a source of energy. It
is not. It is a form of energy that must have a
source. What is the difference between an energy
source and form of energy
60
  • Which of the following are examples of energy
    sources. Which are energy types?
  • a. Electricity
  • b. lightning
  • c. Candy bar
  • d. Heat

61
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62
  • 1. What comes to mind when you heard the phrase
    electric power?
  • N1I1N2I2, solve for I2
  • V1/N1 V2/N2, solve for V2

63
37.5 Transformers
Transformer, a device for increasing or
decreasing voltage through electromagnetic
induction.
64
  • V1 / N1 V2 / N2
  • V1 primary voltage
  • V2 Secondary voltage
  • N1 Number of turns on the primary coil
  • N2 number of turns on the secondary coil

65
What is power
  • Power current voltage
  • PI V
  • I P/V
  • V P/I
  • Unit of power watts

66
2/25
  • What is the purpose of a transformer?
  • A power line has 1200 volts and 1000 turns on the
    input, how many turns are required to step this
    down to 120 volts?

67
37.5 Transformers
A practical transformer uses many coils. The
relative numbers of turns in the coils determines
how much the voltage changes.
68
37.5 Transformers
This transformer lowers 120 V to 6 V or 9 V. It
also converts AC to DC by means of a diode that
acts as a one-way valve.
69
The purpose of a transformer
  • http//www.youtube.com/watch?v20Vb6hlLQSg

70
37.6 Power Transmission
Power transmission uses transformers to increase
voltage for long-distance transmission and
decrease it before it reaches your home.
71
  • Turbine mechanical device that rotates
  • Distribution dividing something up
  • Generator converting mechanical energy into
    electrical energy

72
  • What are three things you can change about the
    induction coil to increase the light bulb
    brightness?

73
36.8 Meters to Motors
  • In a simple DC motor, a permanent magnet produces
    a magnetic field in a region where a rectangular
    loop of wire is mounted.
  • The loop can turn about an axis.
  • When a current passes through the loop, it flows
    in opposite directions in the upper and lower
    sides of the loop.
  • The loop is forced to move as if it were a
    galvanometer.

74
  • What happens when you touch a powerline?
  • Why is this bird still alive?
  • What happens to the electrical charge if the
    distance between two objects is doubled

75
37.8 Electromagnetic Waves
  • An electromagnetic wave is composed of
    oscillating electric and magnetic fields that
    regenerate each other.

76
37.5 Transformers
The relationship between primary and secondary
voltages with respect to the relative number of
turns is
77
  • Calculate the voltage output by the secondary
    winding of a transformer if the primary voltage
    is 20 volts, the secondary winding has 20 turns,
    and the primary winding has 10 turns.
  • V secondary

78
  • What is the difference between a motor and a
    generator?

79
Motors and Generators
  • Electric Motor a device that changes electric
    current into mechanical energy.
  • Generator a device that changes mechanical
    energy into electrical current.

80
37.8 Electromagnetic Waves
  • The shaking charge can be considered an electric
    current.
  • A magnetic field surrounds an electric current.
  • A changing magnetic field surrounds a changing
    electric current.
  • A changing magnetic field creates a changing
    electric field.
  • The changing electric field creates a changing
    magnetic field.

81
37.8 Electromagnetic Waves
  • Nature of Light

Maxwell quickly realized that he had discovered
the solution to one of the greatest mysteries of
the universethe nature of light. Maxwell
realized that radiation of any frequency would
propagate at the same speed as light.
82
37.8 Electromagnetic Waves
An electromagnetic wave is composed of
oscillating electric and magnetic fields that
regenerate each other. No medium is required. The
oscillating fields emanate from the vibrating
charge. At any point on the wave, the electric
field is perpendicular to the magnetic
field. Both are perpendicular to the direction of
motion of the wave.
83
  • 1. What is the difference between a motor and a
    generator?
  • 2. A 120 v power source needs to be powered down
    to 12 v,how many coils would be on the second
    part if the first part had 100 turns?

84
Persistence
  • persisting, especially in spite of opposition,
    obstacles, discouragement,

85
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86
Motor write up
  • Use claim evidence and reasoning format to write
    up your motor lab
  • Claim how do you know it was a motor?
  • Evidence include observations. Explain step by
    step what difficulties did you face. How did you
    make your motor.
  • Reasoning How does a motor work. What two
    forces are necessary? Why is balance important?
    Why did you have to keep part of the coat on?

87
  • Reasoning how does a motor work. What two
    forces are necessary? Why is balance important?
    Why did you have to keep part of the coat on?

88
  • Energy types chemical, mechanical, electrical,
    nuclear, radiant, heat
  • 1. How did you know that you built a motor?
  • 2. What types of energy transitions did your
    motor make?
  • Tomorrow Magnetism Quiz and notebookcheck

89
Assessment Questions
  • A voltage will be induced in a wire loop when the
    magnetic field within that loop
  • changes.
  • aligns with the electric field.
  • is at right angles to the electric field.
  • converts to magnetic energy.

90
Assessment Questions
  • A voltage will be induced in a wire loop when the
    magnetic field within that loop
  • changes.
  • aligns with the electric field.
  • is at right angles to the electric field.
  • converts to magnetic energy.
  • Answer A

91
Assessment Questions
  • If you change the magnetic field in a closed loop
    of wire, you induce in the loop a
  • current.
  • voltage.
  • electric field.
  • all of these

92
Assessment Questions
  • If you change the magnetic field in a closed loop
    of wire, you induce in the loop a
  • current.
  • voltage.
  • electric field.
  • all of these
  • Answer D

93
Assessment Questions
  • The essential concept in an electric motor and a
    generator is
  • Coulombs law.
  • Ohms law.
  • Faradays law.
  • Newtons second law.

94
Assessment Questions
  • The essential concept in an electric motor and a
    generator is
  • Coulombs law.
  • Ohms law.
  • Faradays law.
  • Newtons second law.
  • Answer C

95
Assessment Questions
  • A motor and a generator are
  • similar devices.
  • very different devices with different
    applications.
  • only found in hybrid cars.
  • energy sources.

96
Assessment Questions
  • A motor and a generator are
  • similar devices.
  • very different devices with different
    applications.
  • only found in hybrid cars.
  • energy sources.
  • Answer A

97
Assessment Questions
  • 5. According to James Clerk Maxwell, if the
    magnitude of the created magnetic field
    increases, the change in the electric field will
  • stay the same.
  • increase.
  • decrease.
  • always disappear.

98
Assessment Questions
  • 5. According to James Clerk Maxwell, if the
    magnitude of the created magnetic field
    increases, the change in the electric field will
  • stay the same.
  • increase.
  • decrease.
  • always disappear.
  • Answer B

99
Assessment Questions
  • 6. Moving electric charges are surrounded by
  • only electric fields.
  • only magnetic fields.
  • both magnetic and electric fields.
  • nothing.

100
Assessment Questions
  • 6. Moving electric charges are surrounded by
  • only electric fields.
  • only magnetic fields.
  • both magnetic and electric fields.
  • nothing.
  • Answer C

101
  • What is electromagnetic induction and how is it
    used to create electricity?
  • What causes magnetism?
  • Are you ready for the quiz?
  • Notebook check number of dates from 2/11

102
  • Test taking Silencio por favor
  • aamus
  • a moose

103
Interesting questions
  • Does iron weigh more toward the poles?
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