Electricity and Magnetism

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Electricity and Magnetism

• Section 8.2 8.3

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What is magnetism?

• Properties and interactions of magnets
• Magnets have a magnetic force between them
• This attraction decreases the farther apart they
  are

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Moving Charges and Magnetic Fields

• Moving electrical charges produce a magnetic
  field
• The magnetic field is generated in
  counterclockwise circles around the direction of
  the moving electrons.

• The stronger the current flowing through the wire
  the stronger the magnetic field

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Electron Flow
Magnetic Field

Magnetic Field
Electron Flow
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Electromagnets

• temporary magnet made by placing a piece of iron
  inside a current carrying coil of wire

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• the more loops the greater the strength of the
  magnet
• the greater the current the greater the strength
  of the magnet

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Where can I find electromagnets? (Just to name a
few!)

• stereo speakers
• electric motors
• generators (electric power plants)
• VCRs
• Tape decks
• Computer hard drives

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Galvanometer

• devices that use an electromagnet to measure
  electric current
• (ex gasoline in a tank or the water temperature)

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Electric Motors

• Electric motor device which turns electrical
  energy into mechanical energy through the use of
  an electromagnet

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How do they work?

1. Charge from battery makes coil become magnetized
2. The North end of coil lines up with south end of
   magnet

These are on page 236 in your book.
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• Change direction in the coil is flipped which
  flips the north south ends of the coil so the
  coil rotates to line up with magnet again
• This happens repeatedly to keep the coil rotating
  in the magnet

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Generators

• Generator a device that turns mechanical energy
  into electrical energy using an electromagnet

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How do generators work?

1. Some source of mechanical energy turns a coil
   which is sitting in a permanent magnet
2. As the coil rotates in the magnetic field it
   generates electricity

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Generating Electricity for your Home

• Electromagnets are turned by a turbine a huge
  wheel that rotates when pushed by water, wind, or
  steam.

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Direct Alternating Current

• Batteries produce direct current (DC) current
  flows in only 1 direction
• Generators produce alternating current (AC)
• Current reverses direction periodically
• In North America the current alternates at a
  frequency of 60 Hz
• This is what is sent to our homes by the power
  plants

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Transformers

• Transformer a device that alters the voltage of
  an alternating current
• Two coils of wire wrapped around the same iron
  core
• If the primary coil has less wraps around the
  core than the secondary coil the voltage will
  increase.

Pg. 243 in book
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• A step up transformer is used when the
  electricity leaves the power plant to boost its
  voltage so less energy is lost as heat as it
  travels through the power lines
• Before the electricity enters your house a step
  down transformer is used to lower the voltage to
  the standard 120V