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UNIT FIVE: Electricity and Magnetism

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UNIT FIVE: Electricity and Magnetism. Chapter 16 Electricity Chapter 17 Magnetism. Chapter Seventeen: Magnetism. 17.1 Properties of Magnets 17.2 Electromagnets 17.3 Electric Motors and Generators 17.4 Generating Electricity. Chapter 17.1 Learning Goals.

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unit five electricity and magnetism
UNIT FIVE: Electricity and Magnetism
  • Chapter 16 Electricity
  • Chapter 17 Magnetism
chapter seventeen magnetism
Chapter Seventeen: Magnetism
  • 17.1 Properties of Magnets
  • 17.2 Electromagnets
  • 17.3 Electric Motors and Generators
  • 17.4 Generating Electricity
chapter 17 1 learning goals
Chapter 17.1 Learning Goals
  • Identify properties of magnetic materials and use interactions between magnets to explain attraction and repulsion.
  • Describe the source of Earth’s magnetism.
  • Explain how a compass works.
investigation 17a
Key Question:

How do magnets and compasses work?

Investigation 17A

Magnetism

17 1 properties of magnets
17.1 Properties of Magnets
  • If a material is magnetic, it has the ability to exert forces on magnets or other magnetic materials nearby.
  • A permanent magnet is a material that keeps its magnetic properties.
17 1 properties of magnets1
17.1 Properties of Magnets
  • All magnets have two opposite magnetic poles, called the north pole and south pole.
  • If a magnet is cut in half, each half will have its own north and south poles.
17 1 properties of magnets2
17.1 Properties of Magnets
  • Whether the two magnets attract or repel depends on which poles face each other.
17 1 properties of magnets3
17.1 Properties of Magnets
  • Magnetic forces can pass through many materials with no apparent decrease in strength.
17 1 properties of magnets4
17.1 Properties of Magnets
  • Magnetic forces are used in many applications because they are relatively easy to create and can be very strong.
  • Large magnets create forces strong enough to lift a car or a moving train.
17 1 magnetic fields
17.1 Magnetic fields
  • The force from a magnet gets weaker as it gets farther away.
  • Separating a pair of magnets by twice the distance reduces the force by 8 times or more.
17 1 magnetic fields1
17.1 Magnetic fields
  • A special kind of diagram is used to map the magnetic field.
  • The force points away from the north pole and towards the south pole.
17 1 magnetic fields2
17.1 Magnetic fields
  • You can actually see the pattern of the magnetic field lines by sprinkling magnetic iron filings on cardboard with a magnet underneath.
17 1 magnetic field lines
17.1 Magnetic field lines
  • A compass needle is a magnet that is free to spin.
  • Because the needle aligns with the local magnetic field, a compass is a great way to “see” magnetic field lines.
17 1 geographic and magnetic poles
17.1 Geographic and magnetic poles
  • The planet Earth has a magnetic field that comes from the core of the planet itself.
17 1 geographic and magnetic poles1
17.1 Geographic and magnetic poles
  • The names of Earth’s poles were decided long before people understood how a compass needle worked.

The compass needle’s “north” end is actually attracted to Earth’s “south” magnetic pole!

17 1 declination and true north
17.1 Declination and “true north”
  • Because Earth’s geographic north pole (true north) and magnetic south pole are not located at the exact same place, a compass will not point directlyto the geographic north pole.
  • The difference between the direction a compass points and the direction of true north is called magnetic declination.
17 1 declination and true north1
17.1 Declination and “true north”
  • Magnetic declination is measured in degrees and is indicated on topographical maps.
17 1 declination and true north2
17.1 Declination and “true north”
  • Magnetic declination is measured in degrees and is indicated on topographical maps.
  • Most good compasses contain an adjustable ring with a degree scale used compensate for declination.
17 1 earth s magnetism
17.1 Earth’s magnetism
  • Studies of earthquake waves reveal that the Earth’s core is made of hot, dense molten metals.
  • Huge electric currents flowing in the molten iron produce the Earth’s magnetic field.
17 1 earth s magnetism1
17.1 Earth’s magnetism
  • The gaussis a unit used to measure the strength of a magnetic field.
  • The magnetic field of Earth (.5 G) is weak compared to the field near the ceramic magnets you have in your classroom. (300- 1,000 G).
  • For this reason you cannot trust a compass to point north if any other magnets are close by.
17 1 earth s magnetism2
17.1 Earth’s magnetism
  • Today, Earth’s magnetic field is losing approximately 7 percent of its strength every 100 years.
  • If this trend continues, the magnetic poles will reverse sometime in the next 2,000 years.
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