Download Lesson 5 Magnetism and Electricity Notes

Chapter 12 Lesson 5 Magnetism and Electricity
Vocabulary
1. Attract-
2. Repel-
3. Pole-
4. Magnetic field-
5. Electromagnet-
6. Motor-
7. Generator-
Notes
What is a magnet?
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Magnet-something that can attract iron and certain other metals.
o
Metals include iron, nickel, and cobalt.
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Produce a magnetic field.
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Come in all shapes and sizes.
o
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EX: simple bars, horseshoes, ring shaped.
All magnets have 2 poles.
o
North (N) and South (S).
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North attracts south.
o
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Opposites attract.
North repels North, South repels South.
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Like forces repel.
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Attraction of two magnets is strongest when magnets are closest together.
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Magnetic force gets weaker with distance.
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Metals are made up of tiny particles.
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Each particle acts like a small magnet.
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Particles push and pull in different directions.
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If an iron object nears a magnet, these particles turn around and line up.
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North poles face one direction, south poles face the other.
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The object becomes a temporary magnet.
What are magnetic fields?
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Magnets can pull or push objects without touching them at all.
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Every magnet has a magnetic field that wraps around it.
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Objects can move when the magnetic fields of two magnets overlap.
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Earth is a giant magnet.
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Much of the inside of Earth is made up of melted iron.
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This iron creates a magnetic field.
Earth actually has 2 North Poles.
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Geographic North Pole is located at one end of Earth’s axis.
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Magnetic North Pole is near geographic North Pole, but not in the same spot.
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This is also true of the South Pole.
Magnetic fields are invisible.
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You can use small pieces of iron to see what one looks like.
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A compass is a tool that uses Earth’s magnetic field to show direction.
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The needle of a compass is a thin magnet.
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Compass needles always point north because Earth’s magnetic North Pole attracts the south
pole of the needle.
What is an electromagnet?
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When charged particles move, they form magnetic fields.
o
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This means we can use electric current to make magnets.
Electric current moving through a wire sets up a magnetic field around that wire.
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The more current, the stronger the magnetic field.
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Turn off the current and the field goes away.
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Looping the wire into a long coil will make the magnetic field stronger.
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Each loop in like a little magnet.
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By adding a metal core, you can make the strongest magnetic field of all.
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Current flowing through the coil sets up a magnetic field.
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The particles inside the iron core line up, increasing the magnetic field around the coil.
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An electromagnet can be turned on or off with a switch.
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This is a useful feature in electric devices such as headphones and telephones.
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Electromagnets are often used to power electric motors.
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Electric motors change electrical energy into mechanical energy.
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A simple electric motor has three parts.
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Power source-produces electric current that runs through the wire loop.
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Magnet-pushes and pulls on the electromagnet.
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Wire loop attached to a shaft-usually attaches to a wheel or a gear.
Shaft-rod that can spin.
What is a generator?
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A generator is the opposite of a motor.
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Changes mechanical energy into electrical energy.
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Has the same parts as a motor (power source, magnet, and wire loop attached to a shaft).
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Motion is need to turn the shaft and wire loop.
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The loop rotates between two magnetic poles.
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The magnetic field between the poles produces electric current in the wire loop.
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Each time the loop gets close to the poles, electrical charges are pushed through.
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These moving charges are electric current.
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A turbine is a set of angled blades attached to a shaft.
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A simple turbine looks like an electric fan.
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Steam, water, or air is used to turn the blades of the turbine.
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The turning blades spin the shaft.
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The shaft the spins the wire loop or magnet inside the generator.
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Most turbines are powered by steam.
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The steam is sent through a pipe pointed at the blades.
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Most electric generators produce an alternating current, or AC.
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Alternating current flows in one direction and then flows in the opposite direction.
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Charges flow back and forth continuously.
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Most wall outlets use AC.
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When electric current flows in only one direction, it is called direct current, or DC.
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In DC, charges flow continuously, but do not stop or reverse direction.
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A battery uses DC.
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Some devices, like computers, change AC from wall outlets into DC.
How does electricity get to your home?
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Power plants produce electrical energy.
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Electric current carries the energy to homes.
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The current moves in a circuit that connects to wall outlets.
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Voltage is the strength of a power source.
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Measured in volts.
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Power plants generally produce electric current at about 25,000 volts.
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To prevent loss of power over long distances, the voltage is increased.
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Increasing the voltage reduces the current.
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This reduces energy loss.
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Transformers change the voltage of electric current.
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A step-up transformer boosts the voltage.
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Current from a power plant goes through a step-up transformer.
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It leaves the transformer with a strength of about 400,000 volts.
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Before entering your home, the current must be changed to a lower voltage.
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A step-down transformer decreases the voltage.
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Most home use electric current at 120 or 240 volts.