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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 electrical rely on __________ energy. 21.3 Electrical Energy Generation and Transmission Generating Electric Current How is voltage induced in a conductor? 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 Generating Electric Current A magnetic field can be used to produce an ___________ current. electric Electromagnetic _____________is induction • ________________ the process of generating a current by moving an electrical conductor relative to a magnetic field. 21.3 Electrical Energy Generation and Transmission Generating Electric Current According to Faraday’s law, a voltage is induced magnetic in a conductor by a changing ____________ field. •Changing the magnetic field through a coil of wire voltage induces a ____________ in the coil. •A current results if the coil is part of a complete circuit _____________. 21.3 Electrical Energy Generation and Transmission Generating Electric Current According to Faraday’s law, the moving magnetic current field induces a __________ in the coil. Movement of magnet When magnet is not moving _________, there is no current detected. Coil When magnet is moving, the current changes direction ____________ when the magnet changes direction. Galvanometer shows that the current is flowing. 21.3 Electrical Energy Generation and Transmission Generators 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 mechanical electrical ____________ energy into ___________energy by rotating a coil of wire in a magnetic field. • Electric current is generated by the relative magnetic motion of a conducting coil in a ____________ field. 21.3 Electrical Energy Generation and Transmission Generators The two types of generators are: AC generators 1. ______________________ DC generators 2. ______________________ 21.3 Electrical Energy Generation and Transmission Generators AC Generators alternating An AC generator produces ___________ current ____________, in which charges flow first in one direction and then in the other direction. The generator looks very similar to an electric mechanical motor but converts _______________ energy into electrical _______________ electrical energy instead. 21.3 Electrical Energy Generation and Transmission Generators In a simple AC generator, an _________force external rotates the loop of wire in the magnetic field. This induces a current _________in the wire. Wire loop Slip rings Direction in which the loop is turned 21.3 Electrical Energy Generation and Transmission Generators A wire coil in the generator is attached to metal bands called_________ _________. slip rings • 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 current in the wire, which induces a _________ reverses ___________direction every Wire loop half rotation. Slip rings 21.3 Electrical Energy Generation and Transmission Generators Small generators provide power in areas that are not served by power companies or provide power electrical energy during a __________ outage __________. 21.3 Electrical Energy Generation and Transmission Generators DC Generators direct A DC generator produces a _________ current. • Its design is very much like the design of an AC commutator 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 one _______ direction. 21.3 Electrical Energy Generation and Transmission Transformers transformer A ____________ is a device that increases or decreases the voltage and current of two linked AC circuits. 21.3 Electrical Energy Generation and Transmission Transformers Electrical energy from power plants is transmitted through power lines at voltages ___________ too high to be used safely in homes. changed The voltage must be __________, or transformed. A series of transformers changes high-voltage current in power lines 240-volt into ____________ current. 21.3 Electrical Energy Generation and Transmission Transformers Why Transformers Are Needed DC generators • 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 current and higher _________. voltage ________ • Only AC voltage and current can be transformed ____________. 21.3 Electrical Energy Generation and Transmission Transformers: Changing Voltage and Current A transformer has two sets of coils wrapped around a ringiron shaped ________ core. primary • When there is an alternating current in the __________ coil, the current creates a changing magnetic field in the iron core. secondary • Because the iron core is also inside the ___________ coil, the changing field induces an alternating current in the secondary coil. Step-down Transformer Soft iron core Low voltage High voltage 400 turns 100 turns Step-up Transformer Low voltage High voltage 100 turns 400 turns AC Source AC Source Primary coil Secondary coil 21.3 Electrical Energy Generation and Transmission Transformers turns The number of _________ in the primary and secondary coils determines the voltage and current. divide • To calculate the voltage, __________ the number of turns in the secondary coil by the number of turns in the primary coil. output • The result is the ratio of the __________ voltage to the input voltage. 21.3 Electrical Energy Generation and Transmission Transformers Transformers are very efficient because very little energy is lost as __________. heat • There is also an ___________ relationship inverse between current and voltage. • If voltage ___________ increases in the secondary coil, the current must _____________ decrease in the same ratio. 21.3 Electrical Energy Generation and Transmission Transformers Types of Transformers step-down A ____________ transformer decreases voltage and increases current. • Occurs just before the electrical energy reaches homes people’s ___________. 21.3 Electrical Energy Generation and Transmission Math Calculation 0.25 30 volts 21.3 Electrical Energy Generation and Transmission Transformers step-up A ____________ transformer increases voltage and decreases current. • Occurs when electrical energy _________ leaves the power plant • Makes it an easier and more efficient way to bring electrical energy to houses from transmission long-distance ____________. 21.3 Electrical Energy Generation and Transmission Math Calculation 4 80 volts 21.3 Electrical Energy Generation and Transmission Electrical Energy for Your Home Most of the electrical energy generated in the coal United States is produced using _________ as an energy source. Some other sources are water nuclear energy, ________ (hydroelectric), ________ natural gas, and ___________. petroleum wind, _________ 21.3 Electrical Energy Generation and Transmission Electrical Energy for Your Home turbine 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 electrical _____________ energy. 21.3 Electrical Energy Generation and Transmission Electrical Energy for Your Home To produce electrical energy, the turbine may turn the coils of a _____________, or it generator may spin _____________ magnets around the coils of wire. 21.3 Electrical Energy Generation and Transmission Electrical Energy for Your Home A power plant transmits electrical energy at hundreds of thousands of ________. volts • After the current passes travels through highvoltage transmission lines, the voltage is stepped down at a substation, to a few thousand _____________ volts. • The electrical energy is then distributed and 220 and ______ 240 stepped down to between _______ volts. 240-volt • Appliances like an electric stove use _________ circuits. Most other appliances in the home use 120 volts ___________. 21.3 Electrical Energy Generation and Transmission Assessment Questions 1. In a DC generator, the commutator a. b. c. d. generates an electric current. replaces the slip rings. reduces the voltage. 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. b. c. d. 250 V 500 V 2,000 V 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. b. c. d. current voltage resistance insulation 21.3 Electrical Energy Generation and Transmission Assessment Questions 4. In electromagnetic induction, an electric current is induced by the motion of an electrical conductor relative to a magnetic field. True False