21.3 Electrical Energy Generation and Transmission Photographs of large cities, such as Seattle,...

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


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?


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.


electricElectromagnetic induction



•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


According to Faraday’s law, the moving magnetic field induces a __________ in the coil.


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


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


Generators

The two types of generators are:

1.______________________

2.______________________

AC generators

DC generators


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


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


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


Small generators provide power in areas that are not served by power companies or provide electrical energy during a __________ __________.

Generators

power

outage


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


A ____________ is a device that increases or decreases the voltage and current of two linked AC circuits.

Transformers

transformer


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


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


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


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


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


Types of Transformers

A ____________ transformer decreases voltage and increases current. •Occurs just before the electrical energy reaches people’s ___________.

Transformers

step-down

homes


Math Calculation

0.25

30 volts


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


Math Calculation

4

80 volts


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


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.


turbine

electrical


To produce electrical energy, the turbine may turn the coils of a _____________, or it may spin _____________ around the coils of wire.


generator

magnets


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 ___________.


volts

thousand

220 240

240-volt

120 volts


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.



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



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



4. In electromagnetic induction, an electric current is induced by the motion of an electrical conductor relative to a magnetic field.

TrueFalse

21.3 Electrical Energy Generation and Transmission Photographs of large cities, such as Seattle,...

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