Chapter 12 Lesson 5 Magnetism and Electricity

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18 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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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?



Magnet
-
something that can attract iron and certain other metals.

o

Metals include iron, nickel, and cobalt
.



Produce a magnetic field.



Come in all shapes and sizes.

o

EX: simple bars, horseshoes, ring shaped.



All magnets have 2 poles.

o

North (N) and South (S).



North attracts south.

o

Opposites attract.



North repels North, South repels South.

o

Like forces repel.



Attr
action of two magnets is strongest when magnets are closest together.



Magnetic force gets weaker with distance.



Metals are made up of tiny particles.

o

Each particle acts like a small magnet.



Particles push and pull in different directions.



If an iron object

nears a magnet, these particles turn around and line up.

o

North poles face one direction, south poles face the other.

o

The object becomes a temporary magnet.

What are magnetic fields?



Magnets can pull or push objects without touching them at all.



Every magn
et has a magnetic field that wraps around it.



Objects can move when the magnetic fields of two magnets overlap.



Earth is a giant magnet.

o

Much of the inside of Earth is made up of melted iron.

o

This iron creates a magnetic field.



Earth actually has 2 North P
oles.

o

Geographic North Pole is located at one end of Earth’s axis.

o

Magnetic North Pole is near geographic North Pole, but not in the same spot.

o

This is also true of the South Pole.



Magnetic fields are invisible.

o

You can use small pieces of iron to see what

one looks like.



A compass is a tool that uses Earth’s magnetic field to show direction.



The needle of a compass is a thin magnet.



Compass needles always point north because Earth’s magnetic North Pole attracts the south
pole of the needle.

What is an elec
tromagnet?



When charged particles move, they form magnetic fields.

o

This means we can use electric current to make magnets.



Electric current moving through a wire sets up a magnetic field around that wire.

o

The more current, the stronger the magnetic field.

o

Turn off the current and the field goes away.



Looping the wire into a long coil will make the magnetic field stronger.



Each loop in like a little magnet.



By adding a metal core, you can make the strongest magnetic field of all.



Current flowing through the
coil sets up a magnetic field.



The particles inside the iron core line up, increasing the magnetic field around the coil.



An electromagnet can be turned on or off with a switch.

o

This is a useful feature in electric devices such as headphones and telephone
s.



Electromagnets are often used to power electric motors.



Electric motors change electrical energy into mechanical energy.



A simple electric motor has three parts.

o

Power source
-
produces electric current that runs through the wire loop.

o

Magnet
-
pushes and p
ulls on the electromagnet.

o

Wire loop attached to a shaft
-
usually attaches to a wheel or a gear.



Shaft
-
rod that can spin.


What is a generator?



A generator is the opposite of a motor.

o

Changes mechanical energy into electrical energy.



Has the same parts as a

motor (power source, magnet, and wire loop attached to a shaft).



Motion is need to turn the shaft and wire loop.



The loop rotates between two magnetic poles.



The magnetic field between the poles produces electric current in the wire loop.



Each time the lo
op gets close to the poles, electrical charges are pushed through.



These moving charges are electric current.



A turbine is a set of angled blades attached to a shaft.



A simple turbine looks like an electric fan.



Steam, water, or air is used to turn the bla
des of the turbine.



The turning blades spin the shaft.



The shaft the spins the wire loop or magnet inside the generator.



Most turbines are powered by steam.



The steam is sent through a pipe pointed at the blades.



Most electric generators produce an alterna
ting current, or AC.



Alternating current flows in one direction and then flows in the opposite direction.

o

Charges flow back and forth continuously.

o

Most wall outlets use AC.



When electric current flows in only one direction, it is called direct current, or

DC.



In DC, charges flow continuously, but do not stop or reverse direction.



A battery uses DC.



Some devices, like computers, change AC from wall outlets into DC.


How does electricity get to your home?



Power plants produce electrical energy.



Electric curr
ent carries the energy to homes.



The current moves in a circuit that connects to wall outlets.



Voltage is the strength of a power source.

o

Measured in volts.

o

Power plants generally produce electric current at about 25,000 volts.

o

To prevent loss of power ove
r long distances, the voltage is increased.

o

Increasing the voltage reduces the current.

o

This reduces energy loss.



Transformers change the voltage of electric current.



A step
-
up transformer boosts the voltage.



Current from a power plant goes through a step
-
up transformer.



It leaves the transformer with a strength of about 400,000 volts.



Before entering

your home, the current must be changed to a lower voltage.



A step
-
down transformer decreases the voltage.



Most home use electric current at 120 or 240 volts.