Magnetism

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Unit 11

• Magnetism

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Magnets

• magnetism force of attraction or repulsion
• not all objects are affected by the force of
  magnetism
• ex. wood, glass, paper, plastic
• common metals affected by magnetism are iron,
  nickel, and cobalt

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Magnets

• poles two ends of a magnet
• every magnet has two poles
• north (N) pole
• south (S) pole
• even if you break a magnet in half, each half
  will have a north pole and a south pole

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Magnets

• the north pole of a magnet points North
• it is often called North-seeking

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Properties of Magnets

• if a north pole and a south pole are brought
  together, they will attract each other
• opposites attract

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Properties of Magnets

• if the north pole of one magnet is brought near
  the north pole of another magnet, they will repel
  each other
• if two south poles are brought together, they
  will repel each other

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Properties of Magnets

• like magnetic poles repel each other
• unlike magnetic poles attract each other

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Magnetic Fields

• magnetic field area around a magnet where
  magnetic forces can act
• a magnetic field is made up of magnetic lines of
  force

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Magnetic Fields

• magnetic lines of force lines that show the
  shape of a magnetic field
• the magnetic lines of force are closest together
  at the poles of the magnet
• this is where the magnet is strongest

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Making a Magnet

• some magnets occur in nature
• these magnets are called natural magnets
• ex. magnetite (also called lodestone)

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Making a Magnet

• materials that are not natural magnets can be
  magnetized

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Making a Magnet

• magnetic induction process by which a material
  can be made into a magnet

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Making a Magnet

• some materials are easy to magnetize
• ex. iron

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Making a Magnet

• a material that is easily magnetized tends to
  lose its magnetism quickly
• a magnet made of this kind of material is called
  a temporary magnet

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Making a Magnet

• materials that are hard to magnetize will also
  stay magnetized for a long time
• a magnet that is hard to magnetize but tends to
  keep its magnetism is called a permanent magnet

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The Earth as a Magnet

• William Gilbert
• a British scientist
• the Earth has north and south poles like a bar
  magnet

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The Earth as a Magnet

• the Earth has a North Magnetic Pole and a South
  Magnetic Pole
• the North Magnetic Pole is located near the
  geographic North Pole
• the South Magnetic Pole is located near the
  geographic South Pole

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The Earth as a Magnet

• the North Magnetic Pole is like the south pole of
  a bar magnet
• the South Magnetic Pole is like the north pole of
  a bar magnet

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The Earth as a Magnet

• the Earth is surrounded by a magnetic field which
  extends far into space
• magnetosphere region of the Earths magnetic
  field

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The Earth as a Magnet

• the magnetosphere traps charged particles from
  the sun
• when these particles enter the atmosphere, an
  aurora is formed
• auroras are also called the northern and southern
  lights

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Electricity and Magnetism

• Hans Oersted
• about 200 years ago
• an electric current flowing in a wire causes a
  compass needle to move

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Electricity and Magnetism

• an electric current passing through a wire causes
  a magnetic field

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Electricity and Magnetism

• electromagnetism relationship between
  electricity and magnetism

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Electricity and Magnetism

• Michael Faraday (British scientist)
• Joseph Henry (American scientist)
• when a wire is moved across a magnetic field, an
  electric current is induced in the wire

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Electricity and Magnetism

• electromagnetic induction process by which an
  electric current is produced by moving a wire in
  a magnetic field

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Electricity and Magnetism

• a wire carrying an electric current always has a
  magnetic field around it
• the magnetic field in a straight wire is not very
  strong
• if the wire is wound into a coil, the magnetic
  field becomes much stronger as the individual
  magnetic fields overlap
• the greater the number of coils, the stronger the
  magnetic field

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Electromagnets

• electromagnet temporary magnet made by wrapping
  a current-carrying wire around an iron core
• the center of an electromagnet is called the core
• it is often made of iron

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Electromagnets

• as long as current is flowing, an electromagnet
  has a magnetic field
• when current is turned off, there is no longer a
  magnetic field

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Electromagnets

• there are two ways to make an electromagnet
  stronger
• increasing the number of coils
• increasing the amount of current

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Electromagnets

• electromagnets are useful because they can be
  turned on and off
• electromagnets have many important uses
• ex. radios, telephones, computers

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Electromagnets

• changing the direction of an electric current
  causes the poles of an electromagnet to reverse
• this feature is important in the production of
  electric motors

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Transformers

• transformer device in which alternating current
  in one coil of wire induces a current in a second
  coil

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Transformers

• a transformer consists of two coils of wire
  around a magnet
• the first coil, called the primary coil, is
  connected to the power source
• the second coil, called the secondary coil, is
  connected to the load
• a load is something that uses electricity, such
  as a light bulb or a motor

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Transformers

• a transformer only works with alternating current

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Transformers

• a step-up transformer increases voltage
• it consists of more coils of wire in the
  secondary coil than the primary coil

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Transformers

• a step-down transformer decreases voltage
• it consists of more coils of wire in the primary
  coil than the secondary coil

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Electric Motors

• electric motor device that changes electrical
  energy into mechanical energy

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Electric Motors

• an electric motor is made up of an electromagnet
  and a permanent magnet

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Electric Motors

• the electromagnet is free to turn and is hooked
  up to a source of alternating current
• changing the direction of an electric current
  causes the poles of an electromagnet to reverse

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Electric Motors

• attraction and repulsion between the
  electromagnet and the permanent magnet cause the
  electromagnet to spin

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Electric Motors

• an electric motor can use direct current if a
  special switch is used

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Generators

• generator device that changes mechanical energy
  into electrical energy
• a current can be induced in a loop of wire by
  spinning the loop inside a magnetic field
• due to the changing direction of the wire, an
  alternating current is produced

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Generators

• an electric generator is made up of an insulated
  loop of wire and a U-shaped magnet
• spinning the loop of wire in the magnetic field
  of the magnet produces an electric current

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Generators

• most of the energy we use every day comes from
  generators

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Generators

• mechanical energy for many generators is supplied
  by turbines
• a turbine is a large wheel that is turned by
  moving steam or water