A Length of Wire and Resistance
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Resistance and the Length of Wire
Purpose: In this experiment, a relationship between the resistance of current flow in a wire versus the length of the wire will be investigated. The electrical property of the material the wire is made of will also be explored.
Materials: - wire on meter stick - a multi-meter set to 200
Procedure: 1. Make sure that your multi-meter dial is turned to 200 Ω toward the right side. The screen will read OL. 2. Place one probe of the multi-meter at the end zero position on the meter stick and the other at 10 cm. 3. Read and record the multi-meter in a data table. The meter reading will change and it may take some time to before the value stops. Wait until a value stays for about 5 seconds before recording.
4. Repeat the measurements with the probes 20, 30, 40, etc. cm apart and record. 5. Turn OFF the multi-meter by turning the dial straight up to O.
Length of wire (cm) Resistance (Ω ) 10 20 30 40 50 60 70 80 90 100
6. Graph your data of resistance () v. length of wire (cm). Draw a “line of best fit”, bisecting your data points.
7. Find two new points on your line of best fit and label them. In a corner of your graph paper, calculate the slope of this best fit line. Questions and Analysis
1. What relationship can be found from your graph? Write a sentence that uses both x-axis and y-axis variables and the relationship correctly.
l The formula for the resistance of a conductor is given by R A
Where R represents ______measured in ______Where l represents ______measured in ______Where A represents ______ measured in ______Where represents ______measured in ______
2. Now look carefully at the formula. Which variables are constant? These variables combine to form the slope of your graph. Write these two variables in fraction form and set them equal to your calculated slope.
3. From your equation in question 2, calculate the experimental resistivity (exp) of the wire material.
4. The gauge number of a wire is a reference to its thickness; the larger the number, the thinner the wire. The gauge number of the wire is given, use the attached gauge table to find the cross-sectional area of your wire and record both.
5. From the attached gauge table, determine the type of conductor the wire was made from and calculate the
% error. Use your experimental value (exp)and the accepted value (acc)from the table.
Experimental - Accepted % error = x 100 Accepted
6. Name and explain four factors that can change resistance. Resistivity Table Temperature = 20˚ C l R A Material = Resistivity (Ω cm) Silver 1.59 X 10 –6 Copper 1.72 X 10 –6 Gold 2.44 X 10 –6 Aluminum 2.82 X 10 –6 Tungsten 5.6 X 10 –6 Nickel 7.8 X 10 –6 Platinum 11.0 X 10 –6 Nickelsilver 4.9 X 10 –5 Nichrome 11.5 X 10 –5 Carbon 3.5 x 10 -3 Silicon 640 X 10 2 Glass 1.0 X 10 12 Rubber 1.0 X 10 15
Gauge Number Table “the thickness of a wire” Gauge Number Diameter (cm) Cross Section (cm2) 000 1.040 0.8503 00 0.9266 0.6743 8 0.3264 0.08366 12 0.2053 0.03309 14 0.1628 0.02081 16 0.1291 0.01309 18 0.1024 0.008231 20 0.08118 0.005176 22 0.06438 0.003255 24 0.05106 0.002047 28 0.03969 0.001237 30 0.03175 0.0007917 Formal Lab Report
Formal lab reports will be occasionally assigned and will be worth 50 points. They should be typed, and have a cover page (consisting of a title, “physics”, your name, and the due date, centered on the first page). They should be in the following format:
Purpose: (“To find the relationship between . . .”, etc.) This is the point of why the experiment is being conducted, usually referencing a problem.
Hypothesis: A hypothesis is often referred to as an “educated guess,” which is a prediction that will be tested in the experiment. Not all labs will have a hypothesis. Record a hypothesis before starting the experiment. A hypothesis that is subsequently disproved does not make the hypothesis a failure; there is no need to change the original (previously untested) hypothesis.
Materials: A list of the materials required.
Procedure: A step-by-step description of the experiment, clearly stated.
Data: These are the results of the experiment, presented in one or more of the following formats: tables, graphs, or drawings (the form the data takes is dependent on the experiment). Include sample calculations.
Questions: Record and answer any questions in the lab.
Conclusion: The conclusion should make reference to the problem in the purpose, hypothesis, procedure (especially in terms of the validity of the data), and the data. All conclusions should be driven by the data. It is essential that the student discuss any factors that may have affected the validity of the data, error analysis, and (depending upon the lab) describe how to improve the lab.
Typing symbols: if you type the following letters, highlight the target, and change the font to “symbol”, you will get the following symbols: q w r u p a g l b n m W S D to type “°”, go to the insert and symbol menu.
2 to superscript (x ) or subscript (x2), highlight the target, go to font and check the box