Download 21.3 Electric Energy Generation and Transmission

21.3 Electric Energy
Generation and Transmission
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Think about this…
How does electrical energy affect a city?
Traffic lights change colors to control the flow of cars.
Flashing neon lights advertise businesses.
Without electricity, many activities would have to stop
after the sun goes down.
The question is: Where does
all the electrical energy
come from?
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5
Generating Electric Current
All the electrical energy comes from the two
aspects of the electromagnetic force.
In the last section of this chapter, we learned that
electric current produces a magnetic field.
and a A magnetic field
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can create an electric
current.
This is called electromagnetic induction.
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Generating Electric Current
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Electromagnetic induction
was discovered in 1831
by Michael Faraday (an
English scientist).
According to Faraday’s
law, a voltage is created
in a conductor by a
changing magnetic
field.
How can you change the
magnetic field?
Generating Electric Current
You can change the magnetic field by moving a magnet.
So moving a magnet through a coiled wire that is in a
circuit will produce an electric current.
Once you stop moving the magnet, the current will stop.
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Generating Electric Current
You can also move the coil and keep the magnet
still to produce a current.
The way to produce a current is to have the
magnet and coil move relative to one another.
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Generators
Most of the electrical energy used in homes is
produced with generators at large power plants.
A generator is a device that converts mechanical
energy into electrical energy.
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Generators
Generators contain a turbine - a device with
fanlike blades that turn when pushed.
To produce electrical energy, the turbine rotates
the coils of a generator, or it rotates magnets
around the coils of wire.
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AC Generators
There are two types of generators: AC and DC.
The AC generator produces an alternating current.
How does it work?
A wire coil in the generator is attached to metal
bands called slip rings.
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AC Generators
The slip rings are in contact with metal brushes that
are in turn attached to a circuit.
As the loop of wire is rotated, the magnetic field
induces a current in the wire.
This current is in one direction and then when the
loop turns halfway around, the current reverses
direction.
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DC Generators
A DC generator produces a direct current.
Its design is like the design of an AC generator
except that a commutator replaces the slip rings.
The commutator only allows current to leave in one
direction (thus DC).
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Transformers
Most power plants produce voltages that are too high to
be handled safely in homes.
So, in order for it to be safe, the voltage must first be
changed, or transformed.
This is where a “transformer” comes in.
A transformer is a device
that increases or decreases
the voltage and current of
two linked AC circuits.
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Changing Voltage and Current
There are two types of transformers, a “step-up” and a
“step-down” transformer.
Each transformer has two sets of coils wrapped around
a ring-shaped iron core.
When there is an alternating current in the primary coil,
the current creates a
changing magnetic field in
the iron ring.
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other (secondary) coil.
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Changing Voltage and Current
The step-down transformer decreases voltage.
It does this by having the primary coil have more loops
than the secondary coil.
By having less loops in the secondary coil, the
secondary coil is not able to collect as much of the
magnetic field to help push
electrons through it.
A step-up transformer
increases voltage.
The primary coil has less
loops than the secondary
coil.
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Electrical Energy for Your Home
So in order to power our homes, the power plant
generates electrical energy with generators.
From the power plant, the electricity travels through a
series of transformers, which reduce the voltage
before it gets to our homes.
After this voltage is reduced, then it is safer to use.
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3-end