PASCO EM-8812 Resistance Apparatus - Manual (Page 13)

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M o d e l N o . E M - 8 8 1 2 E x p e r i m e n t 3 : V o l t a g e v e r s u s L e n g th
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7. Set up DataStudio (or the GLX) in Manual Sampling mode to graph V (measured
by the galvanometer) versus (entered manually). See “Appendix: Manual Sam-
pling Mode” below for detailed instructions.
Note that the voltage measured by the galvanometer (V) is the voltage between the
reference and slider probes, not the voltage output of the power supply. Also, the
length ( ) is the distance between the probes, not the end-to-end length of the wire.
Procedure
1. Note the current. Check it occasionally to ensure that it stays constant.
2. Click Start in DataStudio (or press or press on the GLX) to start data moni-
toring.
3. Set the probes for the desired value of (24 cm for the first point).
4. Click Keep in DataStudio (or press or press on the GLX) to record a data
point.
5. When prompted, manually enter the value of .
6. Repeat steps 3 through 5 for lengths of 20 cm, 16 cm, 12 cm, 8 cm, and 4 cm.
7. When you have finished collecting data, click Stop ( ) in DataStudio (or press
or press on the GLX).
8. Apply a linear fit to the V versus graph.
9. Use the slope of the line, the cross-sectional area of the wire, the current, and
Equation 3-3 to calculate
ρ.
10. Repeat this procedure for the other diameters of brass wire. It is not necessary for
the current to be the same for each wire. Higher current (up to, but not over, 2 A)
will give you better data, especially for the largest diameter.
Questions
How do the values of ρ for the four wires compare to each other? How does your
average value of
ρ compare to the accepted value?
Further Study
Repeat the procedure with the copper, aluminum, nichrome, and stainless steel wires
to find their resistivities. Do not use a current over 1 A for the stainless steel wire, or
over 0.5 A for the nichrome wire. Higher current in these wires will cause them to
heat up, which will change their resistivities.
Appendix: Manual Sampling Mode
This experiment calls for manual sampling mode, in which the software or interface
records a single voltage value when commanded by the user and prompts the user to
type in the corresponding length measurement. After connecting the galvanometer to
the interface, follow the instructions below to put DataStudio software or the Xplorer
GLX (used without a computer) into manual sampling mode and setup a voltage ver-
sus length graph.