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Resistors in Series and Parallel, pp. 300–301 Purpose • Students investigate the total resistance of resistors connected in series and in parallel by measuring current and voltage. WHEN TO BEGIN WHAT TO DO 1 class before Remind students to bring a Calculator APPARATUS/MATERIALS Assign Lab Groups based on ability levels 1 day before Gather materials and apparatus For each group: – 4 1.5 volt d Cell in holders – 3 resistors of different sizes (100 _–500 _) – 2 multimeters used as a voltmeter and an ammeter– switch – connecting wires – calculator Alternate Method available using “Virtual Labs Electricity” on the LBJH Intranet. See Alternate lab methodology Safety Precautions • If any components become hot, ensure that students open the switch immediately. • If a power supply is being used instead of batteries ensure that students turn off the power supply while constructing the circuit. Science Background A resistor slows down the flow of electrons in a circuit. If resistors are placed in series, each of the resistors adds to the resistance. Therefore, placing resistors in series increases the total resistance of the circuit. This would be analogous to cars driving over a single-lane bridge. If the road has one bridge, the bridge will create resistance and traffic will slow down. If a second bridge is placed after the first, this will further slow down traffic. The two consecutive bridges create more resistance than a single bridge. Calculating the total resistance for an electric circuit can be done using Ohm’s law. By measuring the current leaving the source of potential (battery) and also measuring the total voltage applied to the circuit by that source, resistance can be calculated (R =V/I ). In Part 1 of this activity, the total resistance of the circuit that is calculated using Ohm’s law is greater than the individual resistors. Resistors placed in parallel create another pathway on which current can travel. If resistors are placed in parallel, the total resistance of the circuit will decrease. Using the bridge analogy, a single bridge creates resistance to the flow of cars on the highway. If a second bridge is placed beside the first, in parallel, traffic is now split between two possible routes. Placing the second bridge in parallel allows more cars to pass over the river in a given time than if only one bridge were present. In Part 2 of this activity, the total resistance of the circuit, calculated using Ohm’s law, is less than that of the individual resistors. Activity Notes • It may be advantageous to have students complete an Admit card before this activity is attempted. (Sample on following page) • It may be advantageous to have students prepare their write-up and data tables before the day of the activity. • Students will need a calculator for this activity. • Using the resistor colour code is not required curriculum learning for students, so the following steps in the Procedure are optional: Part 1 step 2, and Part 2 step 9. You or interested students can refer to the colour codes on student textbook page 277 in Chapter 8, and provide the other students with the values of the resistors. • You may wish to distribute BLM 3-41, Resistors in Series and Parallel, for students to use when recording their data Supporting Diverse Student Needs • Some students may benefit from a review of Ohm’s law from Chapter 8 to ensure success in this activity. • A variety of skills; including interpreting diagrams, building circuits, calculating resistance, and encouraging group members; are necessary to complete this investigation successfully. Ensure that each group includes students with a variety of learning styles. • As an extension, students could be asked to find the relationship between total resistance and individual resistors when connected in either series or parallel Admit Card 1. 1. Using a diagram explain the main difference between an A Series and Parallel Circuit. Series Circuit 2. Parallel Circuit Complete the following Table What are the advantage of a series circuit 1. 2. What are the disadvantages of a series circuit 1. 2. What are the advantages of a parallel circuit 1. 2. What are the disadvantages of a parallel circuit 1. 2. Alternate Lab Methodology As an alternative to the students using lab equipment to perform the Lab it is possible to complete this lab using the virtual lab Electricity software which is found on the student desktop. Student Hand Out Goal • Use these pages to complete Core Lab Conduct an Investigation 9-1F, Resistors in Series and Parallel Question How does the total resistance of a circuit change when resistors are connected in series and in parallel? Procedure Part 1 Resistors in Series 1. Give the table a title. _______________________________________________________ Resistance () Voltage (V) Resistor 1 Voltage across resistor 1 Resistor 2 Voltage across resistor 2 Resistor 3 Voltage across resistor 3 Current (A) Total current leaving the battery Voltage across battery 2. Follow steps 2 to 7 on pages 300 and 301 of Discovering Science 9. Record your data in the table. Part 2 Resistors in Parallel 3. Give the table a title. _______________________________________________________ Resistance () Voltage (z) Resistor 1 Voltage across resistor 1 Resistor 2 Voltage across resistor 2 Current (A) Total current leaving the battery Voltage across battery 4. Follow steps 9 to 15 on page 301 of Discovering Science 9. Record your data in the table. Analyze Part 1 1. Use Ohm’s law (R V I) to calculate the total resistance of your series circuit. (Use the battery voltage and the current leaving the battery.) 2. Compare the total resistance calculated in question 1 to the individual resistors used in the circuit. Is the total resistance greater than or less than the individual resistors? ____________________________________________________________________ 3. Compare the voltage across each resistor. Does each resistor lose the same amount of voltage? ____________________________________________________________________ 4. Add the voltages on each of the three resistors. Compare the total voltage lost on the three resistors to the battery voltage. ____________________________________________________________________ Part 2 5. Use Ohm’s law to calculate the total resistance of your parallel circuit. (Use the battery voltage and the current leaving the battery.) 6. Compare the total resistance calculated in question 5 to the individual resistors used in the circuit. Is the total resistance greater than or less than the individual resistors? ____________________________________________________________________ 7. Compare the voltage across each resistor. Does each resistor lose the same amount of voltage? Conclude and Apply 1. Write a short paragraph that states the relationships of the following terms in a series circuit: total resistance, individual resistors, total voltage, voltage across each resistor. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ 2. Write a short paragraph that states the relationships of the following terms in a parallel circuit: total resistance, individual resistors, total voltage, and voltage across each resistor. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ Analyze Answers Part 1 1. Students’ answers may vary but should be close to the sum of the individual resistors used. 2. The total resistance is greater than each individual resistor. 3. Each resistor loses different voltage. 4. The total voltage lost on the three resistors should be equal to the battery voltage. Part 2 5. Students’ answers may vary but should be less than any of the resistors used. 6. The total resistance is less than each individual resistor. 7. The voltage across each resistor is the same. Conclude and Apply Answers 1. In a series circuit, the total resistance is greater than the individual resistors. The total voltage supplied to the circuit is equal to the sum of the voltages across each resistor. 2. In a parallel circuit, the total resistance is less than the individual resistors. The total voltage supplied to the circuit is equal to the voltage across each resistor.