Electricity Generation and Transformers

1. Photographs of large cities, such as Seattle, Washington, are visible reminders of how much people rely on __________ energy. electrical

2. How is voltage induced in a conductor? Name two types of generators Generating Electric Current How can a transformer change voltage and current? What are some sources of electrical energy in the United States?

3. Generating Electric Current electric 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. Electromagnetic induction

4. Generating Electric Current According to Faraday’s law, a voltage is induced in a conductor by a changing ____________ field. magnetic • 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 _____________. voltage circuit

5. Generating Electric Current current According to Faraday’s law, the moving magnetic field induces a __________ in the coil. Movement of magnet When magnet is moving, the current changes ____________when the magnet changes direction. When magnet is not _________, there is no current detected. direction moving Coil Galvanometer shows that the current is flowing.

6. 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 ____________ 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. mechanical electrical magnetic

7. Generators The two types of generators are: • ______________________ • ______________________ AC generators DC generators

8. Generators alternating 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. current mechanical electrical

9. Generators Wire loop In a simple AC generator, an _________force rotates the loop of wire in the magnetic field. This induces a _________in the wire. external Slip rings current Direction in which the loop is turned

10. Generators slip rings 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. brushes current reverses Wire loop Slip rings

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

12. Generators direct 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. commutator one

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

14. Transformers 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. voltages changed 240-volt

15. Transformers DC generators 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 ____________. current voltage transformed

16. Step-down Transformer Step-up Transformer Soft iron core Low voltage High voltage Low voltage High voltage 400 turns 400 turns 100 turns 100 turns AC Source AC Source Primary coil Secondary coil Transformers: Changing Voltage and Current iron primary 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. secondary

17. Transformers turns 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. divide output

18. Transformers heat 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. inverse increases decrease

19. Transformers step-down Types of Transformers A ____________ transformer decreases voltage and increases current. • Occurs just before the electrical energy reaches people’s ___________. homes

20. Math Calculation 0.25 30 volts

21. Transformers step-up 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 ____________. leaves transmission

22. Math Calculation 4 80 volts

23. 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 nuclear natural petroleum

24. 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 _____________ energy. electrical

25. Electrical Energy for Your Home To produce electrical energy, the turbine may turn the coils of a _____________, or it may spin _____________ around the coils of wire. generator magnets

26. Electrical Energy for Your Home volts 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 ___________. thousand 220 240 240-volt 120 volts

27. Assessment Questions • In a DC generator, the commutator • generates an electric current. • replaces the slip rings. • reduces the voltage. • reverses the direction of the direct current.

28. Assessment Questions • 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? • 250 V • 500 V • 2,000 V • 4,000 V

29. Assessment Questions • Which property would you want to increase in transmitting electrical energy as efficiently as possible over long distances? • current • voltage • resistance • insulation

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