CT-STEM

Overview

In this lesson students will think about ways that physically changing a resistor will change the value of its resistance. This often functions well as an individual brainstorm and then a group/and or class discussion. Whatever list students generate (of "Things that Affect Resistance"), length of resistor, cross sectional area of resistor, and material of resistor should be on that list. These are the things students will be investigating in the lab activity today.

After the brainstorm, students will perform an investigation to actually test 2 of these. Having previously performed the conductors vs insulators investigation, they should already know that material type (~resistivity) matters in terms of resistance. Have a brief conversation with your students to let them know that while they aren't measuring that particular one in this lab, it does matter. I think it's also a good idea to tell them that resistivity is a number assigned to each material, somewhat like density. Every material has one, so if you wanted to calculate the resistance, you would just look up the value of resistivity for the material in question. This value tells the scientist how good of a conductor/insulator the material is.

Standards

Next Generation Science Standards

Engineering, Technology, Applications of Science

[HS-ETS1] Engineering Design

Physical Science

[HS-PS3] Energy

NGSS Crosscutting Concept

Systems
Energy

NGSS Practice

Analyzing Data
Constructing Explanations, Designing Solutions
Using Models
Using Mathematics
Conducting Investigations

Computational Thinking in STEM

Data Practices

Analyzing Data
Collecting Data
Visualizing Data

Modeling and Simulation Practices

Assessing Computational Models
Constructing Computational Models

Computational Problem Solving Practices

Computer Programming
Troubleshooting and Debugging

Credits

Unit designed by Melissa Beemsterboer a teacher at Lindblom.

Activities

1. Brainstorm Variables that Affect the Strength of a Resistor
2. Length vs. Resistance
3. Cross Sectional Area vs. Resistance

Student Directions and Resources

In this activity you will use pencil lead as a resistor and manipulate it to test how certain variables affect the value of the resistance. Recall any good lab practices you have learned in previous years of science. Any time you are doing a lab investigation, you should have best lab practices in mind. You will also need to recall how to use a multimeter.

1. Brainstorm Variables that Affect the Strength of a Resistor

What could affect whether a resistor has high or low resistance? Think quietly to yourself about this first. When your teacher gives you the ok, you can share with your group and/or the class.

Question 1.1

What variables affect the value of resistance in a resistor?

2. Length vs. Resistance

How does length of resistor affect the value of resistance?

Since you cannot measure resistance directly, you will need to measure current (using your multimeter) and then calculate resistance using V=IR. Remember, your goal in this lab is to measure the relationship between length and resistance. These are the two variables that should be in your graph and data table. What you will be actually measuring in the lab is length and current. Once you write down the value of current in each measurement, a group member should immediately calculate resistance, since that's what you actually want.

Change the length of the resistor (pencil lead) by breaking the lead little by little. Make sure to measure the length each time you break it, and always have your two leads connected to the very ends of the lead. If you don't, the length you wrote down will not actually be the length you used.

Question 2.1

Fill in your data below. To add more data, click the + symbol in the bottom row.

Question 2.2

When you are finished filling in your data table, use google sheets to graph resistance vs. length of resistor. Take a screen shot and attach it here!

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Question 2.3

What is the relationship between length of resistor and its resistance?

3. Cross Sectional Area vs. Resistance

How does cross sectional area of the resistor affect the value of resistance?

Since you cannot measure resistance directly, you will need to measure current (using your multimeter) and then calculate resistance using V=IR. Remember, your goal in this lab is to measure the relationship between cross sectional area and resistance. These are the two variables that should be in your graph and data table. What you will be actually measuring in the lab is cross sectional area and current. Once you write down the value of current in each measurement, a group member should immediately calculate resistance, since that's what you actually want.

Change the cross sectional area of the resistor (pencil lead) by grabbing a new piece of thicker or thinner lead each time. You may not get enough data points to be confident about your trend, but you may be able to see a trend if you do your lab to the best of your ability.

Question 3.1