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
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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.
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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.

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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.

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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.

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Section 1 Magnets and Magnetism
Chapter 18
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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.

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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.

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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.

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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.

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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.

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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.

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Section 1 Magnets and Magnetism
Chapter 18
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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.

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Section 1 Magnets and Magnetism
Chapter 18
Earths Magnetic Field
Click below to watch the Visual Concept.
Visual Concept
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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.
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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.

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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.

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Section 2 Magnetism from Electricity
Chapter 18
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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.

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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.

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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.

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Section 2 Magnetism from Electricity
Chapter 18
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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.
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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.

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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.

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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.

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Section 3 Electricity from Magnetism
Chapter 18
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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.

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Section 3 Electricity from Magnetism
Chapter 18
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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.

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Section 3 Electricity from Magnetism
Chapter 18
Transformers, continued
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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

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Electromagnetism
Chapter 18
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Electromagnetism
Chapter 18