1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Objectives Use schematic diagrams to represent circuits. Distinguish between series and parallel circuits. Calculate electric power using voltage and current. Explain how fuses and circuit breakers are used to prevent circuit overload. Chapter 16

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer Section 3 Circuits Chapter 16 1.Inexpensive electrical power is essential. List at least ten electrical devices that you have used today. 2.In some strings of Christmas lights, none of the lights work if one light is burned out. What is a possible explanation for this? 3.A big feast is being prepared for several people in a home. The cooks are using a turkey roaster, the oven, an electric mixer, the blender, and the toaster. Every light is on and so is the refrigerator. All at once the power in the kitchen goes out. What is an explanation for this, and how can it be corrected?

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits What Are Circuits? An electric circuit is a path through which charges can be conducted. An electric circuit is a set of electrical components connected such that they provide one or more complete paths for the movement of charges. The conducting path produced when a light bulb is connected across the battery’s terminals is called a closed circuit. Without a complete path, there is no charge flow and therefore no current. This is called an open circuit. Chapter 16

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electric Circuit Section 3 Circuits Chapter 16

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits What Are Circuits?, continued Switches interrupt the flow of charges in a circuit. You can use a switch to open and close a circuit. Schematic diagrams are used to represent circuits. A schematic diagram is a graphical representation of a circuit that uses lines to represent wires and different symbols to represent components. Each element used in a piece of electrical equipment is represented by a symbol that reflects the element’s construction or function. Chapter 16

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Series and Parallel Circuits Series circuits have a single path for current. When appliances or other devices are connected in a series circuit, they form a single pathway for charges to flow. In a series circuit, the components of a circuit form a single path for current. The current in each device is the same. The resistances may be different. The voltage across each device in a series circuit can be different. If one element along the path in a series circuit is removed, the circuit will not work. Chapter 16

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Series and Parallel Circuits, continued Parallel circuits have multiple paths for current. A parallel circuit is a circuit in which all of the components are connected to each other side by side. The voltage across each device is the same. The current in each device does not have to be the same. A break in any one path in a parallel circuit does not interrupt the flow of electric charge in the other paths. Chapter 16

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Series and Parallel When bulbs are connected in series, charges must pass through both light bulbs to complete the circuit. When devices are connected in parallel, charges have more than one path to follow. The circuit can be complete even if one light bulb burns out. Section 3 Circuits Chapter 16

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Electric Power and Electrical Energy Electrical energy is the energy that is associated with charged particles because of their positions. Electric power is the rate at which electrical energy is used in a circuit. The rate at which electrical work is done is called electric power. Chapter 16 The SI unit for power is the watt (W). 1 W = 1 A  1 V

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Electric Power and Electrical Energy, continued If you combine the electric power equation above with the equation V = IR, the power lost, or dissipated, by a resistor can be calculated. Chapter 16 Electric companies measure energy consumed in kilowatt-hours. 1 kWh = 3.6  10 6 J.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Equation for Electric Power Section 3 Circuits Chapter 16

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Math Skills Electric Power When a hair dryer is plugged into a 120 V outlet, it has a 9.1 A current in it. What is the hair dryer’s power rating? 1.List the given and unknown values. Given: voltage, V = 120 V current, I = 9.1 A Unknown: electric power, P = ? W Chapter 16

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Math Skills, continued 2.Write the equation for electric power. power = current × voltage P = IV 3.Insert the known values into the equation, and solve. P = (9.1 A)(120 V) Chapter 16 P = 1.1 × 103 W

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Fuses and Circuit Breakers When electrical wires carry more than a safe level of current, the circuit is said to be overloaded. A short circuit can happen if a wire’s insulation wears down, two wires may touch, creating an alternative pathway for current. Fuses melt to prevent circuit overloads. A fuse an electrical device that contains a metal strip that melts when current in the circuit becomes too great. Chapter 16

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Fuses and Circuit Breakers Circuit breakers open circuits with high current. A circuit breaker a switch that opens a circuit automatically when the current exceeds a certain value. The circuit breaker acts as a switch. Unlike fuses, circuit breakers can be reset by turning the switch back on. Chapter 16

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Circuits Concept Mapping Chapter 16

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts 1. A 12-volt battery is connected to a light bulb that has a resistance of 240 ohms. Calculate the amount of current in amperes drawn by the circuit. A.0.05 A B.0.5 A C.2.0 A D.20.0 A Standardized Test Prep Chapter 16

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 1. A 12-volt battery is connected to a light bulb that has a resistance of 240 ohms. Calculate the amount of current in amperes drawn by the circuit. A.0.05 A B.0.5 A C.2.0 A D.20.0 A Standardized Test Prep Chapter 16

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 2. Which of the following statements is true? F.Electrical forces exist between any two neutral particles. G.Electrical forces exist between any two charged particles. H.Electrical forces exist only between particles with the same charge. I.Electrical forces exist only between particles with opposite charges. Standardized Test Prep Chapter 16

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 2. Which of the following statements is true? F.Electrical forces exist between any two neutral particles. G.Electrical forces exist between any two charged particles. H.Electrical forces exist only between particles with the same charge. I.Electrical forces exist only between particles with opposite charges. Standardized Test Prep Chapter 16

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 3. What happens to an object that is charged by induction? A.It acquires excess electrons. B.It remains electrically neutral. C.It acquires a net charge from the object that is inducing the charge. D.A current exists between it and the object that is inducing the charge. Standardized Test Prep Chapter 16

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 3. What happens to an object that is charged by induction? A.It acquires excess electrons. B.It remains electrically neutral. C.It acquires a net charge from the object that is inducing the charge. D.A current exists between it and the object that is inducing the charge. Standardized Test Prep Chapter 16

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. A stream of water is deflected when a negatively charged rod is held close to it. Use the concept of induced charge to explain what happens. Standardized Test Prep Chapter 16

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. A stream of water is deflected when a negatively charged rod is held close to it. Use the concept of induced charge to explain what happens. Answer: A charge is induced on the water by the charged rod. Attraction between the charged part of the stream and the rod deflects the flow. Standardized Test Prep Chapter 16

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 5. How does a fuse protect a circuit from overloading? Standardized Test Prep Chapter 16

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 5. How does a fuse protect a circuit from overloading? Answer: The fuse has a thin wire with a low melting point. When electrical resistance increases the temperature too high, it melts and breaks the circuit. Standardized Test Prep Chapter 16

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills In 1909 Robert Millikan measured the charge on an electron in what is known as the oil-drop experiment. He sprayed oil droplets into a chamber. Two plates with opposite charges produced an electric field. Some of the drops acquired a negative charge. The field was adjusted so there was an upward force equal to the downward pull of gravity. From the strength of this force, Millikan could calculate the amount of the electric charge on the drop. 6. Analyze how the electric field could cause an oil drop to float inside the chamber. Standardized Test Prep Chapter 16

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 6. Analyze how the electric field could cause an oil drop to float inside the chamber. Answer: Electrical forces between the charged particle an the charged plates balance the downward pull of gravity. Standardized Test Prep Chapter 16

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 7. Which metal would be the best choice for a power line, based on electrical resistance? F.aluminum G.iron H.lead I.silver Standardized Test Prep Chapter 16

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 7. Which metal would be the best choice for a power line, based on electrical resistance? F.aluminum G.iron H.lead I.silver Standardized Test Prep Chapter 16

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 8. Which metal would most likely be then best substitute for the tungsten filament in an incandescent light bulb based on resistance? A.aluminum B.iron C.lead D.silver Standardized Test Prep Chapter 16

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 8. Which metal would most likely be then best substitute for the tungsten filament in an incandescent light bulb based on resistance? A.aluminum B.iron C.lead D.silver Standardized Test Prep Chapter 16