Magnetism

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Magnetism

• 4th grade Science

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What is a magnet?

• Any object with magnetic force

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Magnetic Poles

• The parts of a magnet where the magnetic force is
  strongest
• All magnets have two poles- a north and a south
  pole
• When two magnets come together, a north and south
  pole attract each other
• Like poles (north-north or south-south) repel
  each other

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Magnetic ForceThe force that pushes magnets
apart or pulls them together

• Magnets that are far apart do not push or pull
  enough to move each other.
• The magnetic force between two magnets is weak
  when magnets are far apart.
• The magnetic force gets stronger as the magnets
  are brought closer together.

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What kinds of materials are attracted to
magnets?What kinds of materials are not
attracted to magnets?

• Lets see...Conduct Investigation!

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Magnetic FieldThe area of magnetic force around
a magnet

• This is how a magnet can attract or repel objects
  without touching them.
• Every magnet has a magnetic field around it.
• The magnetic field is strongest near the magnets
  poles. The magnetic field is weakest farther
  away from the poles.

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Did you know?

• Our planet is a giant magnet. Much of the Earth
  is made of iron which creates a magnetic field
  that surround Earth.
• Long ago people noticed one end of a magnet
  pointed north so they called it the
  north-seeking end. The same happened with the
  south-seeking end. It was shortened to north
  and south poles of a magnet.

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Drawing Conclusions Investigation
Teacher demonstration Why does this happen?
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Michael Faraday and Joseph Henryin 1820s and
1830s

• Made amazing discoveries about electric currents
  and magnets
• They found that electric currents make magnetic
  fields and that magnets could generate an
  electric current.

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What is an electromagnet?

• A magnet formed when electric current flows
  through wire wrapped in coils around an iron bar

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How does an electromagnet work?

• When an electric current flows through the coil,
  it creates a magnetic field.
• This magnetic field causes particles inside the
  metal coil to line up.
• The metal core becomes magnetic.
• When the current stops, the metal core is no
  longer magnetic.

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Lets try it!Build an electromagnet...

• Materials power source (battery), 1 piece of
  wire (50 cm in length), nail
• Investigation
• 1. Wind the wire around a nail 20 times.
• 2. Attach the wire ends to the battery.
• 3. Test it!