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Electromagnetism

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Electromagnetism Chapter 18 Preview Section 1 Magnets and Magnetism Section 2 Magnetism from Electricity Section 3 Electricity from Magnetism Concept Mapping – PowerPoint PPT presentation

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Title: Electromagnetism


1
Electromagnetism
Chapter 18
Preview
Section 1 Magnets and Magnetism Section 2
Magnetism from Electricity Section 3
Electricity from Magnetism
Concept Mapping
2
Section 1 Magnets and Magnetism
Chapter 18
Bellringer
Given the following objects, a piece of aluminum
foil, a nickel, a plastic figure, a piece of
wood, a glass vase, and some paper clips, predict
which objects will be attracted to a magnet. How
do you know? Record your answers in your
science journal.
3
Section 1 Magnets and Magnetism
Chapter 18
Objectives
  • Describe the properties of magnets.
  • Explain why some materials are magnetic and some
    are not.
  • Describe four kinds of magnets.
  • Give two examples of the effect of Earths
    magnetic field.

4
Section 1 Magnets and Magnetism
Chapter 18
Properties of Magnets
  • Magnetic Poles are points on a magnet that have
    opposite magnetic qualities.
  • North and South The pole of a magnet that
    points to the north is called the magnets north
    pole. The opposite end of the magnet, called the
    south pole, points to the south.

5
Section 1 Magnets and Magnetism
Chapter 18
Properties of Magnets, continued
  • Magnetic Forces When you bring two magnets
    close together, the magnets each exert a magnetic
    force on the other. These magnetic forces result
    from spinning electric charges in the magnets.
    The force can either push the magnets apart of
    pull them together.

6
Section 1 Magnets and Magnetism
Chapter 18
7
Section 1 Magnets and Magnetism
Chapter 18
Properties of Magnets, continued
  • Magnetic Fields A magnetic field exists in the
    region around a magnet in which magnetic forces
    can act.

8
Section 1 Magnets and Magnetism
Chapter 18
The Cause of Magnetism
  • Atoms and Domains In materials such as iron,
    nickel, and cobalt, groups of atoms are in tiny
    areas called domains. The north and south poles
    of the atoms in a domain line up and make a
    strong magnetic field.

9
Section 1 Magnets and Magnetism
Chapter 18
The Cause of Magnetism, continued
  • Losing Alignment When domains move, the magnet
    is demagnetized, or loses its magnetic
    properties.
  • Making Magnets You can make a magnet from
    demagnetized material if you line up its domains
    with another magnet.

10
Section 1 Magnets and Magnetism
Chapter 18
The Cause of Magnetism, continued
  • Cutting a Magnet When you cut a magnet in half,
    you end up with two magnets.

11
Section 1 Magnets and Magnetism
Chapter 18
Kinds of Magnets
  • Atoms and Domains Some magnets, called
    ferromagnets, are made of iron, nickel, cobalt,
    or mixtures of those metals. Another kind of
    magnet is the electromagnet. This is a magnet
    made by an electric current.
  • Temporary and Permanent Magnets Temporary
    magnets are made from materials that are easy to
    magnetize. But they tend to lose their
    magnetization easily. Permanent magnets are
    difficult to magnetize, but tend to keep their
    magnetic properties longer.

12
Section 1 Magnets and Magnetism
Chapter 18
Earth as a Magnet
  • One Giant Magnet Earth behaves as if it has a
    bar magnet running through its center.
  • Poles of a Compass Needle The point of a
    compass needle is attracted to the south pole of
    a magnet. Opposite poles of magnets attract each
    other.
  • South Magnetic Pole near North Geographic Pole
    A compass needle points north because the
    magnetic pole of Earth that is closest to the
    geographic North Pole is a magnetic south pole.

13
Section 1 Magnets and Magnetism
Chapter 18
14
Section 1 Magnets and Magnetism
Chapter 18
Earth as a Magnet, continued
  • The Core of the Matter Scientists think that
    the Earths magnetic field is made by the
    movement of electric charges in the Earths core.
  • A Magnetic Light Show Earths magnetic field
    plays a part in making auroras. An aurora is
    formed when charged particles from the sun hit
    oxygen and nitrogen atoms in the air.

15
Section 1 Magnets and Magnetism
Chapter 18
Earths Magnetic Field
Click below to watch the Visual Concept.
Visual Concept
16
Section 2 Magnetism from Electricity
Chapter 18
Bellringer
Suppose you had a machine that could levitate
heavy objects with the flick of a switch. Write a
paragraph in your science journal about how this
machine would make your life easier.
17
Section 2 Magnetism from Electricity
Chapter 18
Objectives
  • Identify the relationship between an electric
    current and a magnetic field.
  • Compare solenoids and electromagnets.
  • Describe how electromagnetism is involved in the
    operation of doorbells, electric motors, and
    galvanometers.

18
Section 2 Magnetism from Electricity
Chapter 18
The Discovery of Electromagnetism
  • Hans Christian Oersted Danish physicist Hans
    Christian Oersted discovered the relationship
    between electricity and magnetism in 1820.
  • More Research From his experiments, Oersted
    concluded that an electric current produces a
    magnetic field. His research was the first
    research in electromagnetismthe interaction
    between electricity and magnetism.

19
Section 2 Magnetism from Electricity
Chapter 18
20
Section 2 Magnetism from Electricity
Chapter 18
Using Electromagnetism
  • A solenoid is a coil of wire that produces a
    magnetic field when carrying an electric current.
  • An electromagnet is made up of a solenoid
    wrapped around an iron core.
  • Turning Electromagnets On and Off
    Electromagnets are very useful because they can
    be turned on and off as needed. The solenoid has
    a field only when there is electric current in
    it.

21
Section 2 Magnetism from Electricity
Chapter 18
Applications of Electromagnetism
  • Doorbells Two solenoids in a doorbell allow the
    doorbell to work.
  • Magnetic Force and Electric Current An electric
    current can cause a compass needle to move. The
    needle is a small magnet. This property is useful
    in electric motors.

22
Section 2 Magnetism from Electricity
Chapter 18
Applications of Electromagnetism, continued
  • An electric motor is a device that changes
    electrical energy into mechanical energy. All
    electric motors have an armaturea loop or coil
    of wire that can rotate.
  • Galvanometers A galvanometer measures current.
    A galvanometer has an electromagnet placed
    between the poles of a permanent magnet.

23
Section 2 Magnetism from Electricity
Chapter 18
24
Section 3 Electricity from Magnetism
Chapter 18
Bellringer
Have you ever discovered something by accident?
Maybe you looked in a dictionary for the
definition of an unknown word, only to find the
definition of another word you didnt know.
Write a short paragraph in your science journal
describing how you have discovered something by
accident.
25
Section 3 Electricity from Magnetism
Chapter 18
Objectives
  • Explain how a magnetic field can make an
    electric current.
  • Explain how electromagnetic induction is used in
    a generator.
  • Compare step-up and step-down transformers.

26
Section 3 Electricity from Magnetism
Chapter 18
Electric Current from a Changing Magnetic Field
  • Faradays Experiment Michael Faraday conducted
    an experiment trying to get the magnetic field of
    the electromagnet to make an electric current in
    a second wire.

27
Section 3 Electricity from Magnetism
Chapter 18
Electric Current from a Changing Magnetic Field,
continued
  • Success for an Instant Faraday realized that
    electric current in the second wire was made only
    when the magnetic field was changing. The process
    by which an electric current is made by changing
    a magnetic field is called electromagnetic
    induction.
  • Inducing Electric Current Look at the next
    slide to see electromagnetic induction.

28
Section 3 Electricity from Magnetism
Chapter 18
29
Section 3 Electricity from Magnetism
Chapter 18
Electric Generators
  • Alternating Current The electric current
    produced by the generator shown on the next slide
    changes direction each time the coil makes a half
    turn. Because the electric current changes
    direction, it is an alternating current.
  • Generating Electrical Energy The energy that
    generators convert into electrical energy comes
    from different sources such as fossil fuels and
    nuclear energy.

30
Section 3 Electricity from Magnetism
Chapter 18
31
Section 3 Electricity from Magnetism
Chapter 18
Transformers
  • A transformer increases or decreases the voltage
    of alternating current.
  • Step Up, Step Down The number of loops in the
    primary and secondary coils of a transformer
    determines whether it increases or decreases the
    voltage.
  • Electrical Energy for Your Home The electric
    current that brings electrical energy to your
    home is usually transformed three times.

32
Section 3 Electricity from Magnetism
Chapter 18
Transformers, continued
33
Electromagnetism
Chapter 18
Concept Mapping
Use the terms below to complete the Concept
Mapping on the next slide.
mechanical energy electromagnetic induction transformers voltage electrical energy electric motor

34
Electromagnetism
Chapter 18
35
Electromagnetism
Chapter 18
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