Lesson 3. Lesson 3 - Measuring Current: Wire Width

Gabriella Anton, Connor Bain
Physics
90 minutes
High School
v2

Overview

Throughout lessons 3, 4, and 5, students will continue to deepen their understanding of how to measure electric current, and how constancy of flow is maintained. Students will develop two different ways to measure current: average current and instantaneous current. Students will be introduced to some computer-based modeling to achieve this. 

In this lesson particularly, students will identify how electric current depends on the width of the wire, as well as the applied voltage. They will also start to explore tools for measuring electric current (sampling different areas of the wire, and comparing the values; averaging) and aggregate data they collect with the class. 

Standards

Next Generation Science Standards
  • Physical Science
  • NGSS Practice
    • Using Models
    • Arguing from Evidence
    • Analyzing Data
    • Communicating Information
Computational Thinking in STEM
  • Data Practices
    • Analyzing Data
    • Collecting Data
    • Visualizing Data
  • Modeling and Simulation Practices
    • Using Computational Models to Understand a Concept
  • Computational Problem Solving Practices
    • Computer Programming
  • Systems Thinking Practices
    • Understanding the Relationships within a System

Activities

  • 1. Current in a Wire Model Introduction
  • 2. Prediction of Current Based on Wire Width
  • 3. Testing Prediction of Wire Width
  • 4. Comparing Data
  • 5. Averaging Data

Student Directions and Resources


In this lesson you will explore how electric current flows in a wire and explore how current depends on applied voltage and wire width. Additionally, you will start to explore ways to measure current and compare data with your classmates. 

1. Current in a Wire Model Introduction


In this activity, you will use a model to identify how electric current depends on applied voltage.

This model shows a microscopic look at how electric current flows through a wire connected to a battery. It shows how electric current depends on the number of free electrons and how fast these red electrons are traveling towards the positive end of a battery. This speed depends on (1) the applied voltage difference and (2) the obstacles that the electrons encounter in their way, which are represented in this model by blue atoms.

In this model, time is represented in terms of ticks, which can be adjusted using the slider at the top to slow down or speed up the model. 

To use the model:

1) Click SETUP then GO. You will start to see electrons flow through the wire, see data readings on the monitors, and a plot form on the graph. 

2) You can change the voltage at any time, even while the model is running. However, to have accurate comparable readings it might be best to hit SET-UP and GO to reset the model after you've changed the parameters to where you'd like them. 


Question 1.1

What do the blue circles represent in the model?



Question 1.2

What do the red circles represent in the model?



Question 1.3

Set the Voltage slider to 0 and click SETUP and then GO. What happens to the current now and the flow of electrons when you decrease the voltage to zero? 



Question 1.4

Increase the Voltage. Click SETUP and then GO. What happens to the current now and flow of electrons as voltage increases? Why do you think this happens?

2. Prediction of Current Based on Wire Width


Now using your explorations with the model, and the screenshot below, make a prediction about how wire width will impact current. 

Consider how electrons might flow differently through a wire that is half as wide. 

 

 

 


Question 2.1

Do you think that with a wire with a smaller width will have a higher or lower current?



Question 2.2

Describe your prediction about how the wire width will impact current and explain your reasoning.

3. Testing Prediction of Wire Width


Use the model to test your hypothesis about how wire width will impact current.

To use the model:

1) Click SETUP then GO. You will start to see electrons flow through the wire, see data readings on the monitors, and a plot form on the graph. 

2) If you'd like to change the wire's width, select 2 or 1 from the drop-down menu WIRE-WIDTH. 


Question 3.1

Try running the model with different wire widths.

First, run FOUR trials of the model with a voltage difference of 1, wire width of 1, and measure the current after 100 ticks (it's okay if you can't get it exactly at 100 ticks!). Once the ticks counter has gotten to your desired time for a trial, hit GO again to stop the model. Then run FOUR trials of the model with a voltage difference of 1, wire width of 2, and measure the current after 100 ticks. 

Input the data collected in the table below. Use the green plus in the upper right corner to add more rows to the table so that you can collect data for all 8 of your trials.



Question 3.2

When the voltage is set at 1 and the samples are about 100 ticks long, how does the wire width impact current? Support your explanation with evidence from the data you collected from the model.



Question 3.3

Please wait for teacher instruction before moving on 

Note: Draw your sketch in the sketchpad below


Question 3.4

What is the average current you found by aggregating data with your class?

4. Comparing Data


Now that you've compared your data list with your classmates' data lists or trials with the same conditions, consider the data you collected on your own and the data collected by the rest of the class. 


Question 4.1

What is the difference between the data you individually generated compared to those generated by the whole class? Which data do you think are more accurate for measuring the current and why?

5. Averaging Data


Now you will look at what happens to the average current after a long period of time. You will see that an average current counter has been added to the model in the lower right corner. 

1) Set the VOLTAGE slider to 1 and the WIRE-WIDTH drop down menu to 1. 

2) Click SETUP then GO. 

3) When your model has gone for at least 600 ticks, hit GO again to stop your model. Take note of the AVERAGE CURRENT


Question 5.1

Which is closer to the model's average current that you found on this page—the current found in an individual trial that you ran on your own on Page 4 or the average current you found as a class after you finished Page 4? Why do you think this is the case?



Question 5.2

Please wait for teacher instruction 

Note: Draw your sketch in the sketchpad below