13.11: Conduct an Investigation
pg. 576
Key Concepts:
1. Circuits are a part of electrical technology. They can be connected in
series and in parallel.
2. Connecting loads in series and parallel affects the current, potential
difference, and total resistance.
3. Current, voltage, and resistance measurements can be used to test
circuits.
The Effect of Increasing the Number of Loads in a Circuit
Testable Question:
How do the total resistance, current, and voltage compare in series and
parallel circuits?
Hypothesis/Prediction:
Experimental Design:
You will connect one load and then two loads in series. Then you will
measure the voltage drop across each resistor, the current through each
resistor, and the resistance of all the resistors in the circuit. You will repeat
the process for a circuit of two loads in parallel. The voltage drop across the
power supply will remain constant throughout the investigation.
Materials:
- Variable DC power supply - voltmeter - ammeter
- connecting leads
- switch
- 2 identical resistors (10.0 Ω)
Simulation web site:
https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc
Procedure:
Part A: Resistors in Series
1. Obtain the equipment and place it at your workbench.
2. Copy table 1, 2 and 3 into your notebook.
3. Connect the circuit shown in Figure 1.
Figure 1
4. Close the switch. Set the power supply to 2 V or as specified by your
teacher. Record this number as the voltage drop across the energy
source.
5. Record the voltage drop across and the current through each resistor
in your table.
6. Turn off the power supply. Then open the switch
7. Add another resistor in series to the circuit. Repeat steps 4 to 6 for
each resistor.
8. Remove the voltmeter and ammeter. Measure the total resistance
across both resistors by placing an ohmmeter as shown in Figure 2.
9. Add third resistor in series to the circuit. Repeat steps 4 to 6 for each
resistor.
Figure 2
Part B: Resistors in Parallel
1. Copy table 4 and 5 into your notebook.
2. Connect the circuit shown in Figure 3.
Figure 3
3. Close the switch. Set the power supply to 2 V or as specified by your
teacher. Record this number as the voltage drop across the energy
source.
4. Measure and record the voltage drop across and the current through
resistor 1
5. Move the meters to measure the values for the second resistor.
6. Turn off the power supply. Then open the switch.
7. Remove the voltmeter and ammeter. Measure the total resistance
across both resistors by placing an ohmmeter as shown in Figure 4.
Record the total resistance.
8. Add third resistor in parallel to the circuit. Repeat steps 3 to 7 for each
resistor.
Figure 4
Observations:
Table 1: One Resistor
Voltage (V)
Current (A)
Resistor 1
Table 2: Two Resistors in Series
Voltage (V)
Resistor 1
Resistor 2
Total Resistance
Current (A)
Table 3: Three Resistors in Series
Voltage (V)
Current (A)
Resistor 1
Resistor 2
Resistor 3
Total Resistance
Table 4: 2 Resistors in Parallel
Voltage (V)
Resistor 1
Resistor 2
Total Resistance
Table 5: 3 Resistors in Parallel
Voltage (V)
Resistor 1
Resistor 2
Resistor 3
Total Resistance
Resistance (Ω)
Resistance (Ω)
Current (A)
Resistance (Ω)
Current (A)
Resistance (Ω)
Analyze and Evaluate:
a) Answer the Testable Question [t/i]
b) Did evidence support your hypothesis? Explain [t/i]
c) Make a statement about the voltage drop across resistors. Compare
resistors in series with resistors in parallel. Also make a statement
comparing the voltage drop across the energy source with voltage drop
across the resistance. [t/i]
d) Make a statement about the currents through resistors. Compare
resistors in series with resistors in parallel. [t/i]
e) Which circuit, series or parallel, would allow more current to flow if
you added one or more resistors? Explain your answer. [t/i]
f) Which arrangement of resistors has greater total resistance, series or
parallel? Explain your choice. Was your hypothesis correct? [t/i]
Apply and Extend:
g) Fire departments warn against plugging too many devices into one
outlet. Using what you have learned in this investigation, explain why
fire departments issue this warning. [app]
h) If you have hot wires, then electrical energy is being used to heat the
wires. Is this an efficient use of electricity? Explain. [app]
i) What would be the advantage of using parallel circuits instead of series
circuits in your home? [app]
Conclusion: