Circuits 3
Exploring the relationship between voltage, current, and resistance.
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CONTENTS
Objectives ............................................................................................................................................. 2
1.1
Experimental Goal ........................................................................................................................ 2
1.2
Prerequisite Skills and Knowledge ............................................................................................... 2
1.3
Research Skills .............................................................................................................................. 2
1.4
Learning Objectives ...................................................................................................................... 2
Pre-Experiment ..................................................................................................................................... 2
2.1
Recap of circuits thus far .............................................................................................................. 2
2.2
Using Excel ................................................................................................................................... 3
2.3
Prepare for the Experiment ........................................................................................................... 4
Laboratory Manual................................................................................................................................ 5
3.1
Materials Check Off List............................................................................................................... 5
3.2
Safety and Waste Disposal Protocols............................................................................................ 5
3.3
Experimental Procedure ................................................................................................................ 5
3.3.1
Measuring Voltage in Series ................................................................................................. 5
3.3.2
Measuring Voltage in Parallel............................................................................................... 5
3.3.3
Voltage, Current, and Resistance: Ohm’s Law ..................................................................... 5
3.4
Post-Lab Assignment .................................................................................................................... 6
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1.1
OBJECTIVES
EXPERIMENTAL GOAL
To describe circuits in a uniform way and to measure current and voltage in a circuit.
1.2
PREREQUISITE SKILLS AND KNOWLEDGE
Students should be able to create circuit diagrams from circuits and vice versa. They should also be able
to recognize which circuits allow current to run through them and which ones don’t. In addition, they
should know how to measure voltages across or currents running through the circuits’ components.
1.3
RESEARCH SKILLS
After this lab, students will have had practice in:
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1.4
Electrical circuits
Circuit diagrams
Graphical analysis
Error analysis
LEARNING OBJECTIVES
After this lab, students will be able to:
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Build a circuit from a circuit diagram and vice versa
Identify parallel and series components in circuits
Report error in voltage and current measurements
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2.1
PRE-EXPERIMENT
RECAP OF CIRCUITS THUS FAR
This is the third experiment in circuits. It might be helpful at this point to review the previous experiments
and to refer to your notebook when answering these questions.
1. To measure the voltage across a component did you connect the component and voltmeter in series or
parallel? Draw a circuit diagram to support your answer.
2. To measure the current running through a component did you connect the component and ammeter in
series or parallel? Draw a circuit diagram to support your answer.
3. Which of the circuits below is set up to measure the current going through only its LED and the
voltage across only its resistor?
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Circuits 3 |3
4. In the following circuit diagram describe where the current moves (from the positive terminal of the
battery all the way to the negative) and which components it moves through.
2.2
USING EXCEL
In the next experiment, you will use Excel to graph data in two variables. Practice today by entering into
Excel and graphing the data shown below.
1.045
1.095
0.224
0.264
1.972
2.026
0.579
0.623
0.342
0.383
3.906
3.974
To create a plot of the first column versus the second column, select both columns so they are highlighted,
then choose “Insert>Charts>Scatter” from the menu. For more instructions search for “scatter plot Excel”.
Right-click on a data point to add a trendline and equation to your plot.
What is the slope and intercept of the plotted line?
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2.3
PREPARE FOR THE EXPERIMENT
Read ahead in the lab manual so you can prepare your laboratory notebook. You will be expected to show
your lab notebook to your instructor at the start of the lab period. When you feel ready, test your
preparation with the Pre-Lab Quiz on e-Learning.
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Circuits 3 |5
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3.1
LABORATORY MANUAL
MATERIALS CHECK OFF LIST
Each small group of (2-3) students will have (in addition to the components provided in Circuits 2 1):
Laptop computer with Microsoft Excel
Four Resistors with their manufacturer provided resistances
3.2
SAFETY AND WASTE DISPOSAL PROTOCOLS
Make sure your circuit is correctly set up before connecting the battery to it. Spent batteries may be tossed
into the ordinary trash.
3.3
EXPERIMENTAL PROCEDURE
As you complete this procedure, be sure to record your actions in your lab notebook, and include the
circuit diagram of each circuit you test.
3.3.1
Measuring Voltage in Series
First examine your battery ports. Set up a circuit with just one battery port, one resister, and a switch.
Leave the switch open until you have confirmed that the circuit is properly assembled. Figure out how to
use your voltmeter to measure the difference in voltage between the port’s input and output.
Q1. How well does the manufacturer’s voltage match what you’ve found?
Describe in your lab notebook how you used the voltmeter to measure the voltage between the two points.
Draw the circuit diagram, showing clearly the connections made by the voltmeter.
Q2. How do you think voltage across the one battery port will differ from that across two, three, or
four batteries in series?
Test your hypothesis by measuring the voltage across two batteries, three batteries, and four batteries in
series. Record your circuit diagram in each case, including the voltmeter.
Q3. Did your predictions match what your results?
3.3.2
Measuring Voltage in Parallel
Now arrange two batteries in parallel.
Q4. How do you think the voltage measured in this configuration will differ from the voltage you
measured above?
Test your hypothesis by measuring the voltage of the above configuration. Record your circuit diagram in
your notebook, including the voltmeter. Record your result in your lab notebook.
Q5. Did your predictions match what your results?
3.3.3
Voltage, Current, and Resistance: Ohm’s Law
Measure the voltage difference across a single conducting wire when it is not hooked up to a battery.
Q6. What do you expect the voltage across a wire to be when there is current flowing through it?
Use a resistor with known resistance and one battery to set up a circuit where the battery port drives a
current through the resistor.
Using the voltmeter, measure the voltage across a single wire.
Q7. Did the measured voltage match your prediction in question 10?
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Now use the ammeter and voltmeter to measure voltage across and current through the resistor. Record
the results and the circuit diagram in your notebook.
Q8. Predict the results (in voltage and current) if you used two batteries instead of one to power your
circuit.
Repeat the previous measurement, using first two and then three, and finally four batteries instead of one
to power your circuit. Record your voltage and current results in Excel.
Use Excel to graph your measured voltage versus current. Try fitting an equation to this graph.
Q9. What is the shape of your graph, and the equation you found for it?
This relationship between current and voltage is known as Ohm’s Law.
Q10. What is the constant that defines the slope of the graphed line?
Q11. How does your measured resistance compare to the resistance stated by the manufacturer?
3.4
POST-LAB ASSIGNMENT
Work with your extended group to submit a one-page abstract in class, describing the experiment you just
completed.
For details, refer to the Abstract Writing Guidelines posted in the Student Resources folder on e-Learning.
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