Closed circuit complete path for electrons follow. Open circuit no charge flow and no current.

Transcription

1 Section 1 Schematic Diagrams and Circuits Electric Circuits, continued Closed circuit complete path for electrons follow. Open circuit no charge flow and no current. short circuit closed circuit, no load. Short circuits can be hazardous.

2 Types of Circuits Series one path for electricity Parallel more than one path or loop.

3 Schematic Diagrams Section 1 Schematic Diagrams and Circuits schematic diagram representation of a circuit. symbols used table in book Any device in a circuit = load

4 Section 1 Schematic Diagrams and Circuits Electric Circuits, continued Voltage source is emf (electromotive force). Battery generator. The potential difference across loads in a circuit equals the terminal voltage

5 Light Bulb Section 1 Schematic Diagrams and Circuits

6 Factors affecting resistance Cross sectional area of conductor Length of conductor Type of conductor Temperature of conductor

7 Honors

8 Section 2 Resistors in Series or in Parallel Resistors in Series or in Parallel

9 Section 2 Resistors in Series or in Parallel Resistors in Series

10 Section 2 Resistors in Series or in Parallel Resistors in Series, Ohms law multiple resistors in a series circuit = effect on the current as one equivalent resistor. I V R eq I= current in amperes (amps) V= voltage =(volts) R= resistance (ohms)

11 Kirchhoff's Rules The sum of the current entering a junction must equal the current leaving The sum of the potential difference across all the elements in a circuit must be 0. batteries supply voltage and loads use it.

12 Section 2 Resistors in Series or in Parallel Sample Problem Resistors in Series A 9.0 V battery is connected to four light bulbs, as shown at right. Find the R eq and total current.

13 Section 2 Resistors in Series or in Parallel Sample Problem, continued Resistors in Series 3. Calculate Substitute the values into the equation and solve: R = 2.0 Ω Ω Ω Ω eq R = 18.0 Ω eq Substitute the equivalent resistance value into the equation for current. V 9.0 V I 0.50 A R 18.0 Ω eq

14 Section 2 Resistors in Series or in Parallel Resistors in Series, continued Series circuits require all elements to conduct electricity urrent.

15 Section 2 Resistors in Series or in Parallel Resistors in Parallel A parallel =two or more loads of a circuit that provide separate paths for current.

16 Section 2 Resistors in Series or in Parallel Resistors in Parallel

17 Section 2 Resistors in Series or in Parallel Resistors in Parallel, continued Resistors in parallel have the same V. The sum of currents in parallel resistors equals the total current. The equivalent resistance of resistors in parallel 1 R eq 1 R 1 1 R 2 1 R 3...

18 Section 2 Resistors in Series or in Parallel Sample Problem Resistors in Parallel A 9.0 V battery is connected to four resistors, as shown at right. Find the equivalent resistance for the circuit and the total current in the circuit.

19 Section 2 Resistors in Series or in Parallel Sample Problem, continued Resistors in Parallel 3. Calculate Substitute the values into the equation and solve: = R 2.0 Ω 4.0 Ω 5.0 Ω 7.0 Ω eq = R Ω Ω Ω Ω Ω eq 1 Ω R eq = = Ω 1.09

20 ` Section 2 Resistors in Series or in Parallel Resistors in Parallel 3. Calculate, continued Substitute the equivalent resistance value into the equation for current. I V R eq 9.0 V Ω I 9.8 A

21 Objectives Section 3 Complex Resistor Combinations Calculate the equivalent resistance for a complex circuit involving both series and parallel portions. Calculate the current in and potential difference across individual elements within a complex circuit.

22 Section 3 Complex Resistor Combinations Resistors Combined Both in Parallel Many complex and circuits in can Series be understood by isolating segments that are in series or in parallel and simplifying them to their equivalent resistances. Work backward to find the current in and potential difference across a part of a circuit.

23 Section 3 Complex Resistor Combinations Analysis of Complex Circuits

24 Sample Problem Section 3 Complex Resistor Combinations Equivalent Resistance Determine the equivalent resistance of the complex circuit shown below.

25 Section 3 Complex Resistor Combinations Sample Problem, continued Equivalent Resistance Reasoning The best approach is to divide the circuit into groups of series and parallel resistors. This way, the methods presented in Sample Problems A and B can be used to calculate the equivalent resistance for each group.

26 Section 3 Complex Resistor Combinations Sample Problem, continued Equivalent Resistance 1. Redraw the circuit as a group of resistors along one side of the circuit. Because bends in a wire do not affect the circuit, they do not need to be represented in a schematic diagram. Redraw the circuit without the corners, keeping the TIP: For now, disregard the emf source, and work only with the resistances. arrangement of the circuit elements the same.

27 Section 3 Complex Resistor Combinations Sample Problem, continued Equivalent Resistance 2. Identify components in series, and calculate their (b) are in series. equivalent resistance. Resistors in group (a) and For group (a): R eq = 3.0 Ω Ω = 9.0 Ω For group (b): R eq = 6.0 Ω Ω = 8.0 Ω

28 Section 3 Complex Resistor Combinations Sample Problem, continued Equivalent Resistance 3. Identify components in parallel, and calculate their equivalent resis-tance. Resistors in group (c) are in parallel R 8.0Ω 4.0Ω 1Ω 1Ω 1Ω R eq eq 2.7 Ω

29 Section 3 Complex Resistor Combinations Sample Problem, continued Equivalent Resistance 4. Repeat steps 2 and 3 until the resistors in the circuit are reduced to a single equivalent resistance.the For remainder group (d): of the Rresistors, 9.0Ω group 2.7Ω 1.0Ω (d), are eq in series. R eq 12.7Ω

30 Sample Problem Section 3 Complex Resistor Combinations Current in and Potential Difference Across a Resistor Determine the current in and potential difference across the 2.0 Ω resistor highlighted in the figure below.

31 Section 3 Complex Resistor Combinations Sample Problem, continued Current in and Potential Difference Across a Resistor Reasoning First determine the total circuit current by reducing the resistors to a single equivalent resistance. Then rebuild the circuit in steps, calculating the current and potential difference for the equivalent resistance of each group until the current in and potential difference across the 2.0 Ω resistor are known.

32 Section 3 Complex Resistor Combinations Sample Problem, continued Current in and Potential Difference Across a Resistor 1. Determine the equivalent resistance of the circuit. The equivalent resistance of the circuit is 12.7 Ω, as calculated in the previous Sample Problem.

33 Section 3 Complex Resistor Combinations Sample Problem, continued Current in and Potential Difference Across a Resistor 2. Calculate the total current in the circuit. Substitute the potential difference and equivalent resistance in V = IR, and rearrange V 9.0 V the equation I to find the current 0.71 A delivered by the battery. Req 12.7 Ω

34 Section 3 Complex Resistor Combinations Sample Problem, continued 3. Determine a path from the equivalent resistance found in step 1 to the 2.0 Ω resistor. Review the path taken to find the equivalent resistance in the figure at right, and work backward through this path. The equivalent resistance for the entire circuit is the same as the equivalent resistance for group (d). The center resistor in group (d) in turn is the equivalent resistance for group (c). The top resistor in group (c) is the equivalent resistance for group (b), and the right resistor in group (b) is the 2.0 Ω resistor.

35 Section 3 Complex Resistor Combinations Sample Problem, continued Current in and Potential Difference Across a Resistor 4. Follow the path determined in step 3, and calculate the current in and potential difference across each equivalent resistance. Repeat this process until the desired values are found.

36 Section 3 Complex Resistor Combinations Sample Problem, continued 4. A. Regroup, evaluate, and calculate. Replace the circuit s equivalent resistance with group (d). The resistors in group (d) are in series; therefore, the current in each resistor is the same as the current in the equivalent resistance, which equals 0.71 A. The potential Given: difference I = 0.71 across A R the = Ω Ω resistor in group Unknown: (d) can be V calculated =? using V = IR. V = IR = (0.71 A)(2.7 Ω) = 1.9 V

37 Section 3 Complex Resistor Combinations Sample Problem, continued 4. B. Regroup, evaluate, and calculate. Replace the center resistor with group (c). The resistors in group (c) are in parallel; therefore, the potential difference across each resistor is the same as the potential difference across the 2.7 Ω equivalent resistance, which equals 1.9 V. The current in the 8.0 Ω resistor in group (c) can be calculated using V = IR. Given: V = 1.9 V R = 8.0 Ω Unknown: I =? I V 1.9 V 0.24 A R 8.0 Ω

38 Section 3 Complex Resistor Combinations Sample Problem, continued 4. C. Regroup, evaluate, and calculate. Replace the 8.0 Ω resistor with group (b). The resistors in group (b) are in series; therefore, the current in each resistor is the same as the current in the 8.0 Ω equivalent I 0.24 A resistance, which equals 0.24 A. The potential difference across the 2.0 Ω resistor can be calculated using V = IR. Given: I = 0.24 A R = 2.0 Ω Unknown: V =? V IR (0.24 A)(2.0 Ω) V 0.48 V

39 Standardized Test Prep Multiple Choice 1. Which of the following is the correct term for a circuit that does not have a closed-loop path for electron flow? A. closed circuit B. dead circuit C. open circuit D. short circuit

40 Standardized Test Prep Multiple Choice, continued 1. Which of the following is the correct term for a circuit that does not have a closed-loop path for electron flow? A. closed circuit B. dead circuit C. open circuit D. short circuit

41 Standardized Test Prep Multiple Choice, continued 2. Which of the following is the correct term for a circuit in which the load has been unintentionally bypassed? F. closed circuit G. dead circuit H. open circuit J. short circuit

42 Standardized Test Prep Multiple Choice, continued 2. Which of the following is the correct term for a circuit in which the load has been unintentionally bypassed? F. closed circuit G. dead circuit H. open circuit J. short circuit

43 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the circuit elements contribute to the load of the circuit? A. Only A B. A and B, but not C C. Only C D. A, B, and C

44 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the circuit elements contribute to the load of the circuit? A. Only A B. A and B, but not C C. Only C D. A, B, and C

45 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the equivalent resis-tance of the circuit? F. R R R G. H. R J. eq A B R R R eq eq A B I V R R R R eq A B C

46 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the equivalent resis-tance of the circuit? F. R R R G. H. R J. eq A B R R R eq eq A B I V R R R R eq A B C

47 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the current in the resistor? A. B. C. D. I I I I I B V R I I I I A B C eq B total A B V R B

48 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the current in the resistor? A. B. C. D. I I I I I B V R I I I I B B A B C eq total V R B A

49 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the equivalent resis-tance of the circuit? F. R R R R G. H. R J. R eq A B C R R R R eq eq eq A B C I V 1 1 RA RB R C 1

50 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the equivalent resis-tance of the circuit? F. R R R R G. H. R J. R eq A B C R R R R eq eq eq A B C I V 1 1 RA RB R C 1

51 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the current in resistor B? A. B. C. D. I I I I I B V R I I I I A B C eq B total A B V R B B

52 Standardized Test Prep Multiple Choice, continued Use the diagram below to answer questions Which of the following is the correct equation for the current in resistor B? A. B. C. D. I I I I I B V R I I I I B B A B C eq total V R B B A

53 Standardized Test Prep Multiple Choice, continued 8. Three 2.0 Ω resistors are connected in series to a 12 V battery. What is the potential difference across each resistor? F. 2.0 V G. 4.0 V H. 12 V J. 36 V

54 Standardized Test Prep Multiple Choice, continued 8. Three 2.0 Ω resistors are connected in series to a 12 V battery. What is the potential difference across each resistor? F. 2.0 V G. 4.0 V H. 12 V J. 36 V

55 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 9. What is the potential difference across each bulb? A. 1.5 V B. 3.0 V C. 9.0 V D. 27 V

56 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 9. What is the potential difference across each bulb? A. 1.5 V B. 3.0 V C. 9.0 V D. 27 V

57 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 10. What is the current in each bulb? F. 0.5 A G. 3.0 A H. 4.5 A J. 18 A

58 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 10. What is the current in each bulb? F. 0.5 A G. 3.0 A H. 4.5 A J. 18 A

59 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 11. What is the total current in the circuit? A. 0.5 A B. 3.0 A C. 4.5 A D. 18 A

60 Standardized Test Prep Multiple Choice, continued Use the following passage to answer questions Six light bulbs are connected in parallel to a 9.0 V battery. Each bulb has a resistance of 3.0 Ω. 11. What is the total current in the circuit? A. 0.5 A B. 3.0 A C. 4.5 A D. 18 A

61 Short Response Standardized Test Prep 12. Which is greater, a battery s terminal voltage or the same battery s emf? Explain why these two quantities are not equal.

62 Standardized Test Prep Short Response, continued 12. Which is greater, a battery s terminal voltage or the same battery s emf? Explain why these two quantities are not equal. Answer: A battery s emf is slightly greater than its terminal voltage. The difference is due to the battery s internal resistance.

63 Standardized Test Prep Short Response, continued 13. Describe how a short circuit could lead to a fire.

64 Standardized Test Prep Short Response, continued 13. Describe how a short circuit could lead to a fire. Answer: In a short circuit, the equivalent resistance of the circuit drops very low, causing the current to be very high. The higher current can cause wires still in the circuit to overheat, which may in turn cause a fire in materials contacting the wires.

65 Standardized Test Prep Short Response, continued 14. Explain the advantage of wiring the bulbs in a string of decorative lights in parallel rather than in series.

66 Standardized Test Prep Short Response, continued 14. Explain the advantage of wiring the bulbs in a string of decorative lights in parallel rather than in series. Answer: If one bulb is removed, the other bulbs will still carry current.

67 Standardized Test Prep Extended Response 15. Using standard symbols for circuit elements, draw a diagram of a circuit that contains a battery, an open switch, and a light bulb in parallel with a resistor. Add an arrow to indicate the direction of current if the switch were closed.

68 Standardized Test Prep Extended Response, continued 15. Using standard symbols for circuit elements, draw a diagram of a circuit that contains a battery, an open switch, and a light bulb in parallel with a resistor. Add an arrow to indicate the direction of current if the switch were closed. Answer:

69 Standardized Test Prep Extended Response, continued Use the diagram below to answer questions For the circuit shown, calculate the following: a. the equivalent resistance of the circuit b. the current in the light bulb. Show all your work for both calculations.

70 Standardized Test Prep Extended Response, continued Use the diagram below to answer questions For the circuit shown, calculate the following: a. the equivalent resistance of the circuit b. the current in the light bulb. Show all your work for both calculations. Answer: a. 4.2 Ω b. 2.9 A

71 Standardized Test Prep Extended Response, continued Use the diagram below to answer questions After a period of time, the 6.0 Ω resistor fails and breaks. Describe what happens to the brightness of the bulb. Support your answer.

72 Standardized Test Prep Extended Response, continued Use the diagram below to answer questions Answer: The bulb will grow dim. The loss of the 6.0 Ω resistor causes the equivalent resistance of the circuit to increase to 4.5 Ω. As a result, the current in the bulb drops to 2.7 A, and the brightness of the bulb decreases.

73 Standardized Test Prep Extended Response, continued 18. Find the current in and potential difference across each of the resistors in the following circuits: a. a 4.0 Ω and a 12.0 Ω resistor wired in series with a 4.0 V source. b. a 4.0 Ω and a 12.0 Ω resistor wired in parallel with a 4.0 V source. Show all your work for each calculation.

74 18. Find the current in and potential difference across each of the resistors in the following circuits: a. a 4.0 Ω and a 12.0 Ω resistor wired in series with a 4.0 V source. b. a 4.0 Ω and a 12.0 Ω resistor wired in parallel with a 4.0 V source. Show all your work for each calculation. Answers: a. 4.0 Ω: 0.25 A, 1.0 V 12.0 Ω: 0.25 A, 3.0 V b. 4.0 Ω: 1.0 A, 4.0 V Chapter 18 Standardized Test Prep Extended Response, continued

75 Standardized Test Prep Extended Response, continued 19. Find the current in and potential difference across each of the resistors in the following circuits: a. a 150 Ω and a 180 Ω resistor wired in series with a 12 V source. b. a 150 Ω and a 180 Ω resistor wired in parallel with a 12 V source. Show all your work for each calculation.

76 Standardized Test Prep Extended Response, continued 19. Find the current in and potential difference across each of the resistors in the following circuits: a. a 150 Ω and a 180 Ω resistor wired in series with a 12 V source. b. a 150 Ω and a 180 Ω resistor wired in parallel with a 12 V source. Answer: a.150 Ω: A, 5.4 V Show 180 Ω: all your A, work 6.5 Vfor each calculation. b. 150 Ω: A, 12 V 180 Ω: A, 12 V

77 Diagram Symbols Section 1 Schematic Diagrams and Circuits