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23 SERIES AND PARALLEL CIRCUITS Vocabulary Review For each description on the left, write the letter of the matching item. ________ 1. a circuit in which there is only one current path a. ammeter ________ 2. a short piece of metal that melts if a current that is too large passes through it b. circuit breaker ________ 3. the occurrence when a circuit forms that has a very low resistance ________ 4. a circuit in which there are several different paths for a current ________ ________ ________ 5. 6. 7. c. combination series-parallel circuit d. equivalent resistance e. fuse an automatic switch that opens a circuit when the current reaches some set value, stopping electric charge flow f. ground-fault interrupter g. parallel circuit a circuit that has some branches in parallel and some in series h. series circuit i. short circuit the value of a single resistor that could replace all resistors in a circuit without changing the current j. voltage divider ________ 8. a device used to measure the current in part of a circuit ________ 9. a device used to measure the potential difference between two points ________ 10. a device that detects small differences in current caused by an extra current path and opens the circuit ________ 11. a series circuit used to produce a voltage source from a higher-voltage battery k. voltmeter SECTION 1 Simple Circuits In your textbook, read about currents in series circuits. Circle the letter of the choice that best completes the statement or answers the question. 1. The current is ____ a series circuit. a. higher at the beginning of c. lower at the beginning of b. the same everywhere in d. variable in Chapter 23 Series and Parallel Circuits 1 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 16 23 2. In an electric circuit, the potential difference provided by the generator or other energy source, Vsource, is equal to the ____ of drops in electric potential across the resistors. a. difference c. sum b. product d. average 3. Which of the following equations is not correct? a. I Vsource/(R1 R2) c. I Vsource/(R1 R2 R3) b. I Vsource/(R) d. I R3 (Vsource)/(R1 R2) 4. Which of the following equations computes the equivalent resistance for a series circuit with four resistors? a. R R1 R2 R3 R4 c. 1/R 1/R1 1/R2 1/R3 1/R4 b. R R1 R2 R3 R4 d. R R1 R2 R3 R4 5. In a series circuit, the equivalent resistance is ____ any single resistance. a. larger than c. equal to b. determined by d. smaller than 6. If the potential difference across the battery does not change, adding more devices in the series ____ the current. a. sometimes decreases c. sometimes increases b. always decreases d. always increases 7. To find the current in a series circuit, first calculate the ____ . a. potential difference c. power b. equivalent resistance d. equivalent voltage In your textbook, read about drops in electric potential in series circuits. Answer the following questions. Use complete sentences. 8. Why must the net change in potential be zero as electric charge moves through a circuit? ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ 9. How do you find the potential difference across an individual resistor? ____________________________________________________________________________________ 10. What type of circuit is used as a voltage divider? ____________________________________________________________________________________ Chapter 23 Series and Parallel Circuits 2 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 23 11. What is the purpose of a voltage divider? ____________________________________________________________________________________ ____________________________________________________________________________________ 12. What determines the resistance of a photoresistor? ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ 13. Name a device that employs the special qualities of a photoresistor. How does this device work? ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ In your textbook, read about parallel circuits. Refer to the circuit diagram below to answer questions 14–18. Circle the letter of the choice that best answers each question. 14. What type of circuit does the diagram represent? a. a series circuit c. a combination series-parallel circuit b. a parallel circuit d. a tandem circuit 15. How many current paths are in this circuit? a. one c. four b. three d. five 16. How would you calculate the total current of this circuit? a. Find the average of the currents through each path. b. Subtract the currents through each path. c. Add the currents through each path. d. It is not possible to calculate total current for this circuit. Chapter 23 Series and Parallel Circuits 3 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 23 17. If the 10- resistor were removed from the circuit, which would not be true? a. The current through the 20- resistor would be unchanged. b. The sum of the current in the branches of the circuit would change. c. The total current through the generator would change. d. The current through the 50- resistor would change. 18. Which of the following is true for this circuit? a. The equivalent resistance of this circuit is smaller than 10 . b. R R1 R2 R3 c. R 1/R1 1/R2 1/R3 d. R R1 R2 R3 SECTION 2 Applications of Circuits In your textbook, read about safety devices. For each statement below, write true or rewrite the italicized part to make the statement true. 1. _________________________ When appliances are connected in parallel, each additional appliance placed in operation reduces the equivalent resistance in the circuit and causes more charge to flow through the wires. 2. _________________________ A short, thin piece of metal in a fuse melts to break an overloaded circuit. 3. _________________________ When a circuit breaker opens, it allows charge to flow in the circuit. 4. _________________________ Ground-fault interrupters can be used to detect small differences in current caused by an extra current path. 5. _________________________ Electric circuits at home are primarily series circuits. 6. _________________________ Low resistance causes the current to be very small and may result in a short circuit. In your textbook, read about combined series-parallel circuits. Answer the following question. Use complete sentences. 7. Describe the strategy you would use to calculate resistance in a combined series-parallel circuit. ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Chapter 23 Series and Parallel Circuits 4 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 23 Circle the letter of the choice that best answers the following question. 8. Which diagram represents a combined series-parallel circuit in which a 30- resistor and a 75- resistor are connected in parallel to a 125-V source through a 2- resistor in series? a. c. b. d. In your textbook, read about ammeters and voltmeters. Refer to the circuit diagram below to answer questions 9a–c. 9. Redraw the circuit diagram according to the following directions. a. Insert a voltmeter that would measure the potential difference across the 10- resistor. b. Insert an ammeter in the circuit that would measure the current of the entire circuit. c. Insert an ammeter in the circuit that would measure the current through the 60- resistor. Chapter 23 Series and Parallel Circuits 5 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 23 Write the term that correctly completes the statement. 10. _________________________ A(n) ____ measures the potential difference across a resistor. 11. _________________________ A(n) ____ measures current. 12. _________________________ The resistance of a voltmeter should be as ____ as possible so that it will change the current as little as possible. 13. _________________________ The resistance of an ammeter should be as ____ as possible so that it will change the current as little as possible. 14. _________________________ An ammeter is placed in ____ with the resistor if you want to measure the current through the resistor. 15. _________________________ A voltmeter should be connected in ____ with a resistor to measure the potential difference across that resistor. 16. _________________________ A(n) ____ always has low resistance and is connected in series. 17. _________________________ A voltmeter always has ____ resistance and is connected in ____ with the part of the circuit being measured. 18. _________________________ The result of connecting a(n) ____ across a resistor is to lower the potential difference across it. 19. _________________________ The higher the ____ of a voltmeter, the smaller the voltage change. 20. _________________________ If you want to measure the current in a branch or part of a circuit, use a(n) ____ . Chapter 23 Series and Parallel Circuits 6 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Study Guide Teacher Support SERIES AND PARALLEL CIRCUITS 11. A voltage divider produces a voltage source of desired magnitude from a higher-voltage battery. All numerical answers have been rounded to the correct number of significant figures. 12. The resistance of a photoresistor depends on the amount of light that strikes it. A photoresistor is made of material that naturally has a higher resistance in the dark. Vocabulary Review 1. h 2. e 3. i 13. A circuit that includes a photoresistor is used in a light meter. The electronic circuit detects the potential difference and converts it to a measurement of illuminance. 4. g 5. b 6. c 14. b 7. d 15. b 8. a 16. c 9. k 17. d 10. f 18. a 11. j SECTION 2 Applications of SECTION 1 Simple Circuits Circuits 1. b 1. true 2. c 2. true 3. d 3. closes 4. a 4. true 5. a 5. parallel 6. b 6. large 7. b 7. First draw a schematic of the circuit. Then reduce the problem to a set of series circuits and a set of parallel circuits. Combine the resistances of the parallel circuits into one circuit, and calculate the single equivalent resistance that can replace them. That leaves only a series circuit. Add the resistors in series to calculate the equivalent resistance. 8. The circuit’s electrical energy source raises the potential by an amount equal to the drop in electric potential produced when the current passes through the resistors. If the net electric potential difference did not equal zero, the circuit would violate the law of conservation of energy. 9. Multiply the current in the circuit by the resistance of the individual resistor. 8. a 10. A series circuit is used as a voltage divider. Chapter 23 Series and Parallel Circuits 7 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Study Guide 9. Teacher Support A B C 10. voltmeter 11. ammeter 12. high 13. low 14. series 15. parallel 16. ammeter 17. high, parallel 18. voltmeter 19. resistance 20. ammeter Chapter 23 Series and Parallel Circuits 8 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.