Module 4: Resistance and Resistivity
In this experiment, you will investigate how the resistance of a conductor is determined by the geometry of the conductor placed in a circuit, and the type of metal from which it is made.
Objectives
- Construct a circuit according to a circuit diagram
- Collect data for the voltage measured at several distances along a conducting wire,
- Apply Ohm's Law to determine the current in a series circuit.
- Calculate the resistivity for a conductor from the linear regression analysis of the resistance of a wire as a function of its length.
- Predict and verify how a conductor's resistance will change as the thickness of the conductor decreases.
Read the Lab Document Download Lab Document
First, read through the instructional lab document to familiarize yourself with the experiment. This lab should take a total of 4 hours to complete.
Download the Excel Workbook Download Excel Workbook
Download the excel workbook template and use it to record your data, complete your analysis, and answer comprehension questions. Remember to save your data often. Use the Excel Workbook as a guide as you read through the lab document. The workbook is not designed to replace the instructions.
Lab Set Up and Data Collection
OBJECTIVE:
Calculate the resistivity of two types of conductors and evaluate how changing the geometry of a conductor affects its measured resistance.
Lab Materials and Setup Videos -
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Lab Materials
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Setup Videos |
Safety: Working with Brass and Nichrome Wire
Your wire will be rolled up for shipping. Before connecting the wire to the board as described on the apparatus, work to straighten the wire by placing your hands about a meter apart on the wire and pull in opposite directions. Take care not to let your hands slide across the wire, as it may slice your skin. Although this has not happened to your instructors, we can imagine that someone who slides their fingers rapidly across the wire may inadvertently cause a cut.
You may choose to wear gloves when stretching the wire, or wrap your hand with a sock or other soft material to provide a barrier between the wire and your hands to prevent injury.
Resistors
This is the first lab where you will utilize a small ceramic resistor. Warning: these are very tiny and can easily get misplaced. Further, they present a choking hazard if swallowed. Please keep the resistors away from small children.
Excel: Formulas and Plots
In this lab, you will use Excel to perform calculations for you, by programming any cell that is shaded yellow with a formula which references values in other cells. To do this successfully, you should understand how Excel assigns locations to cells in a grid pattern, and also how to turn any cell into one which will perform calculations. This link from Microsoft does a good job with each of these skills:
Second, you'll need to create a XY scatter plot which will use one column of values as the x coordinate, and a second column of values as the y coordinate. This tutorial from Excel-Easy will show you how to create a XY scatter plot.
https://www.excel-easy.com/examples/scatter-chart.html Links to an external site.
Please make sure that the correct quantity is plotted on the y axis, and that the correct quantity is plotted on the x axis. Sometimes Excel gets things switched around. If you find that excel has switched the axis, you will need to edit the Data Series for the chart and switch the cells it's identified to plot on the x axis with the cells its identified to plot on the y axis.
Switching Data Range: Right click on the chart area until you find the option to select "Select Data" listed. Then click on the "Series1" in the left column and select "Edit". Here's where you'll find the screen where you can flip what is plotted on the x and y axis.
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Finally, you'll need to perform a linear trendline analysis and ask Excel to provide the trendline equation for the best fit line informed by your data. Here's more on that:
Discussion Posting
Post your plot of RL vs. L for the thin brass wire and the calculation of your percent error for the resistivity of brass from the thin wire, the thick wire, and the resistivity for nichrome wire.
If you have any tips you'd like to share, please also include this as well in a discussion post.
Upload and Submit
Upload your excel workbook containing your data and comprehension questions before the due date indicated on the calendar to the assignment: Lab 4 - Resistance and Resistivity Lab Report