Download Resistors in Series and Parallel DI lab

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.