# University Physics, Lab 4: Resistivity Measurement

In this laboratory experiment, you will measure the resistivity (ρ) of a Copper and Nickel wire.

Equipment:

Five-Cenco coils mounted on a base (see the wire diameter printed in the base), Ammeter, Voltmeter, leads, power supply, Rheostat (30 Ω), Single throw switch (S).

Theory:

Resistivity (ρ) in Ohm-m, length (L) in m, Resistance (R) in Ohms.

Procedure:

Connect the circuit as shown.  Keep the power supply off until your instructor checks your circuit.  Power supply voltage should be around 5.00 V, and the rheostat’s adjustable slide at the middle. Current can be changed the by moving the sliding conductor on the rheostat while keeping the voltage constant.  Fill in the following information from the set-up, and the table from your measurements.

Coil #________Diameter (in)_________Length (m)____________

 Voltage (V) Current I (A) R = V/I 1 2 3 4 5 6

Reproduce this table on your paper as need for other wires.

Use a spreadsheet like excel to find the slope from linear regression.  To do this on excel, enter your voltage (Volt) in the second column and your current (A) in the second column in an excel session.  Highlight both data by dragging the mouse across the data cells while right button is held down.  From the top menu bar, choose graph icon.  Select XY scatter graph, and finish it after going through the suggested steps.  Once you obtained the graph, click anywhere on the graph area.  Choose chart from menu bar, and click on “add trend-line”.  From the options bar check “show equation” and “R value” (this is not Resistance).

Report the followings:

1)      Slope of the equation is the resistance R of the wire.

2)      Accepted value of the resistivity ρ for the wire.

3) Resistivity. Use the slope (R) to calculate the resistivity ρ of the copper and    compare with the book value.

4) Calculate the percentage error as usual (see previous hand-out for formula). Report all of these results in your lab-report.  Reports are due one week after the lab work.

Write a conclusion.  See the lab write-up format on the net (www.utm.edu/~cerkal/cahit.htm): if this site doesn’t work probably need to add an l at the end (…../cahit.html) or start from Geology, Geography and Physics home page.