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# UNIT FIVE: Electricity and Magnetism - PowerPoint PPT Presentation

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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Presentation Transcript

• Chapter 16 Electricity

• Chapter 17 Magnetism

• 17.1 Properties of Magnets

• 17.2 Electromagnets

• 17.3 Electric Motors and Generators

• 17.4 Generating Electricity

• 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.

How do magnets and compasses work?

Investigation 17A

Magnetism

• 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.

• 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.

• Whether the two magnets attract or repel depends on which poles face each other.

• Magnetic forces can pass through many materials with no apparent decrease in strength.

• 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.

• 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.

• 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.

• You can actually see the pattern of the magnetic field lines by sprinkling magnetic iron filings on cardboard with a magnet underneath.

• 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.

• The planet Earth has a magnetic field that comes from the core of the planet itself.

• 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!

• 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.

• Magnetic declination is measured in degrees and is indicated on topographical maps.

• 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.

• 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.

• 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.

• 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.