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21.3 Electrical Energy Generation and Transmission
Photographs of large cities, such as Seattle, Washington, are visible reminders of how much people rely on __________ energy.
electrical
21.3 Electrical Energy Generation and Transmission
How is voltage induced in a conductor?
Generating Electric Current
Name two types of generators
How can a transformer change voltage and current?
What are some sources of electrical energy in the United States?
21.3 Electrical Energy Generation and Transmission
A magnetic field can be used to produce an ___________ current.
• ________________ _____________is the process of generating a current by moving an electrical conductor relative to a magnetic field.
Generating Electric Current
electricElectromagnetic induction
21.3 Electrical Energy Generation and Transmission
Generating Electric Current
•Changing the magnetic field through a coil of wire induces a ____________ in the coil. •A current results if the coil is part of a complete _____________.
According to Faraday’s law, a voltage is induced in a conductor by a changing ____________ field. magnetic
voltage
circuit
21.3 Electrical Energy Generation and Transmission
According to Faraday’s law, the moving magnetic field induces a __________ in the coil.
Generating Electric Current
Coil
Galvanometer shows that the current is flowing.
Movement of magnet
current
When magnet is not _________, there is no current detected.
moving
When magnet is moving, the current changes ____________when the magnet changes direction.
direction
21.3 Electrical Energy Generation and Transmission
Most of the electrical energy used in homes and businesses is produced at large power plants using generators.
• A generator is a device that converts ____________ energy into ___________energy by rotating a coil of wire in a magnetic field.
• Electric current is generated by the relative motion of a conducting coil in a ____________ field.
Generators
mechanical electrical
magnetic
21.3 Electrical Energy Generation and Transmission
Generators
The two types of generators are:
1.______________________
2.______________________
AC generators
DC generators
21.3 Electrical Energy Generation and Transmission
AC Generators
An AC generator produces ___________ ____________, in which charges flow first in one direction and then in the other direction.
The generator looks very similar to an electric motor but converts _______________ energy into _______________ electrical energy instead.
Generators
alternating
current
mechanical
electrical
21.3 Electrical Energy Generation and Transmission
In a simple AC generator, an _________force rotates the loop of wire in the magnetic field. This induces a _________in the wire.
Generators
Wire loop
Slip rings
Direction in which the loop is turned
external
current
21.3 Electrical Energy Generation and Transmission
A wire coil in the generator is attached to metal bands called_________ _________.
• The slip rings are in contact with metal _________ that are in turn attached to a circuit.
• As the loop of wire is rotated, the magnetic field induces a _________ in the wire, which ___________direction every half rotation.
Generators
Wire loop
Slip rings
slip rings
brushes
currentreverses
21.3 Electrical Energy Generation and Transmission
Small generators provide power in areas that are not served by power companies or provide electrical energy during a __________ __________.
Generators
power
outage
21.3 Electrical Energy Generation and Transmission
DC Generators
A DC generator produces a _________ current. • Its design is very much like the design of an AC
generator except that a _____________ replaces the slip rings.
• As opposite sides of the commutator touch the brush, the current that leaves the generator flows in only _______ direction.
Generators
direct
commutator
one
21.3 Electrical Energy Generation and Transmission
A ____________ is a device that increases or decreases the voltage and current of two linked AC circuits.
Transformers
transformer
21.3 Electrical Energy Generation and Transmission
Electrical energy from power plants is transmitted through power lines at ___________ too high to be used safely in homes.
The voltage must be __________, or transformed. A series of transformers changes high-voltage current in power lines into ____________ current.
Transformers
voltages
changed
240-volt
21.3 Electrical Energy Generation and Transmission
Why Transformers Are Needed• Early power plants used _______________
because the power plants were close to the customers.
• Over long distances, the resistance of transmission wires causes large losses of power, which can be reduced by using lower ________ and higher _________.
• Only AC voltage and current can be ____________.
Transformers
DC generators
current voltage
transformed
21.3 Electrical Energy Generation and Transmission
A transformer has two sets of coils wrapped around a ring-shaped ________ core.
• When there is an alternating current in the __________ coil, the current creates a changing magnetic field in the iron core.
• Because the iron core is also inside the ___________ coil, the changing field induces an alternating current in the secondary coil.
Transformers: Changing Voltage and Current
100 turns
Primary coil
Step-down Transformer
Low voltageSoft iron core
High voltage
400 turns
AC Source
Step-up Transformer
High voltageLow voltage
100 turns 400 turns
AC SourceSecondary coil
ironprimary
secondary
21.3 Electrical Energy Generation and Transmission
The number of _________ in the primary and secondary coils determines the voltage and current.
• To calculate the voltage, __________ the number of turns in the secondary coil by the number of turns in the primary coil.
• The result is the ratio of the __________ voltage to the input voltage.
Transformersturns
divide
output
21.3 Electrical Energy Generation and Transmission
Transformers are very efficient because very little energy is lost as __________.
• There is also an ___________ relationship between current and voltage.
• If voltage ___________ in the secondary coil, the current must _____________ in the same ratio.
Transformers
heat
inverse
increasesdecrease
21.3 Electrical Energy Generation and Transmission
Types of Transformers
A ____________ transformer decreases voltage and increases current. •Occurs just before the electrical energy reaches people’s ___________.
Transformers
step-down
homes
21.3 Electrical Energy Generation and Transmission
A ____________ transformer increases voltage and decreases current. •Occurs when electrical energy _________ the power plant•Makes it an easier and more efficient way to bring electrical energy to houses from long-distance ____________.
Transformersstep-up
leaves
transmission
21.3 Electrical Energy Generation and Transmission
Electrical Energy for Your Home
Most of the electrical energy generated in the United States is produced using _________ as an energy source. Some other sources are ________ (hydroelectric), ________ energy, wind, _________ gas, and ___________.
coal
water nuclearnatural petroleum
21.3 Electrical Energy Generation and Transmission
A ____________ is a device with fanlike blades that turn when pushed, for example, by water or steam.•A turbine converts energy from various sources (i.e. coal, nuclear energy, etc) into _____________ energy.
Electrical Energy for Your Home
turbine
electrical
21.3 Electrical Energy Generation and Transmission
To produce electrical energy, the turbine may turn the coils of a _____________, or it may spin _____________ around the coils of wire.
Electrical Energy for Your Home
generator
magnets
21.3 Electrical Energy Generation and Transmission
A power plant transmits electrical energy at hundreds of thousands of ________.
• After the current passes travels through high-voltage transmission lines, the voltage is stepped down at a substation, to a few _____________ volts.
• The electrical energy is then distributed and stepped down to between _______ and ______ volts.
• Appliances like an electric stove use _________ circuits. Most other appliances in the home use ___________.
Electrical Energy for Your Home
volts
thousand
220 240
240-volt
120 volts
21.3 Electrical Energy Generation and Transmission
Assessment Questions
1. In a DC generator, the commutator a. generates an electric current.
b. replaces the slip rings.
c. reduces the voltage.
d. reverses the direction of the direct current.
21.3 Electrical Energy Generation and Transmission
Assessment Questions
2. A transformer has 400 turns on the primary coil and 1600 turns on the secondary coil. What is the output voltage if the input is 1,000 volts? a. 250 Vb. 500 Vc. 2,000 Vd. 4,000 V
21.3 Electrical Energy Generation and Transmission
Assessment Questions
3. Which property would you want to increase in transmitting electrical energy as efficiently as possible over long distances? a. current
b. voltage
c. resistance
d. insulation