Chapter 14: Magnets

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Chapter 14 Magnets
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Magnets

• Some materials can be made into permanent
  magnets.
• Ex Iron?easy to magnetize, but loses it easily
• Cobalt?hard to magnetize, but doesnt lose it
  easily
• Magnets exert magnetic forces on each other.
• Ex nail can be temporary magnet.
• Like pole repel, opposite poles attract.

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Magnetic Fields

• Used to detect magnetic force.
• The traits of magnetic fields
• Lines farther apart? weaker field
• Strongest at poles
• Compasses can track magnetic fields.
• Points in direction that lies along magnetic
  field.

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• Earths magnetic field is like a bar magnet.
• Core too hot to retain magnetic properties.
• Magnetic field changes?171 reversals in 71
  million yrs. (magnetization preserved in
  sea-floor rocks)
• Earths magnetic poles arent the same as
  geographic poles (for now).
• N means north-seeking and S means
  south-seeking for historical reasons.

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Magnets Electricity

• Electric currents produce magnetic fields.
• Right hand rule thumb direction of current
• fingers direction of magnetic
  field
• Magnetic field of a coil of wire resembles a bar
  magnet.
• Solenoid long, wound coil of insulated wire.
• Electromagnet magnetic field created by current
• Ex Junk yard magnet
• Magnetism is caused by moving charges
• Domain area of magnetic field

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• Electromagnetic devices
• Galvanometers detect measure current voltage.
• Electric motors convert electrical energy to
  mechanical energy.
• Stereo speakers use magnetic force to produce
  sound.

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Electric Currents from Magnetism

• Electromagnetic induction production of a
  current in a conducting circuit by a change in
  strength, position, or orientation of an external
  magnetic field.
• Faradays Law an electric current is produced
  in a circuit by a changing magnetic field.
• Some bacteria contain magnetosomes, which align
  with the magnetic field. Human brain cells also
  contain magnetite crystals.

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• Generators convert mechanical energy to
  electrical energy.
• Generators produce electrical energy to use in
  home, but not efficient.
• Alternating current (AC) electric current
  changes directions at regular intervals.
• Ex outlets in your house.

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• Electromagnetic wave consists of electrical
  magnetic field waves at right angles.
• Transformers can change AC and increase or
  decrease voltage.
• Real transformers contain 1000s of turns.

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Galvanometer
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Electric Motor
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Transformers
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References

• Bar Magnet, Solenoid, Earths Poles, Right-hand
  Rule, Electromagnet Pics http//hyperphysics.phy
  -astr.gsu.edu/hbase/magnetic/elemag.html
• Magnet Clipart http//www.nvtech.com
• Magnetic Field Pic http//www.physics.brown.edu/
  physics/demopages/Demo/em/demo/5h1030.gif
• Magnetic Domains http//www.wfu.edu/physics/pira
  /pira200/eandm/5g2030.gif
• Physical Science Magnetism. Discovery Channel
  School. 2002.unitedstreaming. 5 December
  2006http//www.unitedstreaming.com/