electricity, sound and light chapter eight: electricity and magnetism 8.1 electricity 8.2 electrical...
TRANSCRIPT
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Electricity, Sound and Light
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Chapter Eight: Electricity and Magnetism
• 8.1 Electricity
• 8.2 Electrical Circuits and Electrical Power
• 8.3 Properties of Magnets
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Investigation 8B
• What are the properties of magnets?
Magnetism
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8.3 Properties of Magnets
• If a material is magnetic, it has the ability to exert forces on magnets or other magnetic materials.
• A magnet is a material that can create magnetic effects by itself.
Which of these is a permanent magnet?
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8.3 The magnetic field
• A magnet fills the space around itself with a kind of potential energy called the magnetic field.
• You can see the pattern of the magnetic field by sprinkling iron filings on cardboard then placing a magnet underneath.
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8.3 The magnetic field• 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.
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8.3 How does a compass work?
• A compass needle is a magnet that is free to spin.
• The north pole of a compass needle always points toward the south pole of a permanent magnet.
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8.3 How does a compass work?
• The planet Earth has a magnetic field that comes from the core of the planet itself.
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8.3 How does a compass work?• When you use a compass, the north-pointing end of
the needle points toward a spot near (but not exactly at) Earth’s geographic north pole.
• The south magnetic pole of the planet is near the geographic North Pole.
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8.3 The effect of current on a magnet
• In 1819, Hans Christian Øersted placed a compass needle near a wire in a circuit.
• When a switch in the circuit was closed, the compass needle moved just as if the wire were a magnet.
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8.3 Magnetic forces and electric current
• A magnet made with wires and electric current is called an electromagnet.
• The electromagnet produces a magnetic field exactly the same as a permanent magnet with its north and south poles.
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8.3 The right hand rule
• When the fingers of your right hand curl in the direction of current, your thumb points toward the electromagnet’s north pole.
• You can switch the north and south poles of an electromagnet by reversing the direction of the current in the coil.
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8.3 Magnetic forces and electric current
• The metals iron, nickel, and cobalt have strong magnetic properties.
• Both permanent magnets and iron owe their magnetic properties to their atoms.
• Iron atoms can easily rotate their magnetic poles to line up with neighboring atoms.
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8.3 Electric generators and induction• The process of using a
moving magnet to create electric current or voltage is called electromagnetic induction.
• A moving magnet induces electric current to flow in a circuit.
• The word “induce” means “to cause to happen.”
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8.3 Transformers
• A transformer changes the high voltage from the main power lines to the 120 volts your appliances use.
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8.3 Transformers• Inside a transformer, the
input is connected to the primary coil.
• The output of the transformer is connected to the secondary coil.
• The two coils have different numbers of turns to convert from one voltage to another.
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8.3 Alternating current• Your house uses alternating current or AC at
either 120 or 220 volts. • AC voltage reverses direction 60 times per
second.
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Technology Connection
Household Electricity
• You use electric current every day.
• When you plug in an electric appliance, you connect it to a circuit created by wires in the walls.
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Activity
• Electricity and magnetism are two forms of the same basic force.
• You will use this idea to create a small motor.
Make a Simple Motor