Physics 2402
Department of Physics and Geology
Resistivity
Purpose:
To understand the dependence of the electric conductivity of a wire on material, length. and cross section.
Materials:
Frederiksen Power Supply 0-24V AC/DC 3630.00
Extech Instruments AC/DC Clamp Meter 380950
RSR M9803R RMS Multimeter
Assorted connecting wires
Connecting wire alligator clips
Resistivity Coils
Theory:
The resistance R of an electrical conductor depends on:
(1) The type of material it is composed of
(2) Its length L
(3) Its cross sectional area A and
(4) Its temperature.
The dependence on L and A is very simple:
For example a wire of length 4m has twice as much resistance as a 2m length of the same wire. The larger
the cross sectional area the greater the current flow (less resistance) for a given voltage. The material
property of resistance is characterized by the resistivity, p. Some values for some common substances are
given below.
Substance
Copper
Silver
Nichrome
Nickel-Silver
Copper-Nickel
Table 1
Resistivity ( m)
1.72x10-8
1.6x10-8
1.5 x10-6
33 x10-8
5.0 x10-7
Strictly speaking the resistivity does not only depend on the material but also on the temperature; for
metals usually it increases with increasing temperature. However we will neglect this temperature
dependence in this lab. The values in table 1 are valid at room temperature. In this lab you will measure
the resistivities of several different wires and compare your results with those in the table.
Experimental Procedure:
1) Plug the Frederiksen Power Supply 0-24V AC/DC 3630.00 and RSR M9803R RMS Multi-meter in the
wall socket using universal power cable. DO NOT TURN ON DEVICES
2) Connect a red wire to the (+DC) port on the Frederiksen Power Supply 0-24V AC/DC 3630.00 to the
Number 2 terminal on the resistivity coils.
3) Connect a red wire to the red wire on terminal 2 on the resistivity coil to the red port labeled (VΩHZ) on
the RSR M9803R RMS Multi-meter.
4) Connect a blue/black wire from the (–DC) port on the Frederiksen Power Supply 0-24V AC/DC 3630.00 to
the black port labeled (COM) on the RSR M9803R RMS Multi-meter.
5) Connect a blue/black wire from the black port labeled (COM) on the RSR M9803R RMS Multi-meter to
terminal 1 on the resistivity coil.
6) Using the Extech Instruments AC/DC Clamp Meter 380950; clamp the red wire coming from the
Frederiksen Power Supply 0-24V AC/DC 3630.00 to terminal 2
7) Turn on the Frederiksen Power Supply 0-24V AC/DC 3630.00 with the switch located on the right of the
face.
8) Using the left knob on the
side of the Frederiksen Power Supply 0-24V AC/DC 3630.00 to read 3V
9) Turn off the Frederiksen Power Supply 0-24V AC/DC 3630.00.
10) Turn on RSR M9803R RMS Multi-meter with the switch located in the rear of the device.
11) Turn the knob on RSR M9803R RMS Multi-meter to the position that reads V with a solid line over a
dashed line.
Revised December 2011
12) Turn knob on Extech Instruments AC/DC Clamp Meter 380950 to the yellow
with a solid line with a
dashed lined under the solid line.
13) Turn on the Frederiksen Power Supply 0-24V AC/DC 3630.00.
14) Quickly read the Voltage on the RSR M9803R RMS Multi-meter and the Amperage on the Extech
Instruments AC/DC Clamp Meter 380950.
15) Turn off the Frederiksen Power Supply 0-24V AC/DC 3630.00
16) Log results of voltage and amperage in table 2.
17) Repeat steps 12-15 for terminals 2,3,4,and 5.
18) Use Table 3 to do the calculations in Table 2.
Questions:
1) Why is it important to turn off the Frederiksen Power Supply 0-24V AC/DC 3630.00 after recording each
voltage and amperage?
2) What effects does heat have on the coils?
3) How do the electrons travel through the coils?
4) What would happen if we doubled the length of the coils?
5) What would happen if we doubled the diameter of the coils?
Table 2
Wire
Material
1
2
3
4
5
Revised December 2011
Voltage
(V)
Current
(A)
R=V/I
( )
length
(m)
Crosssectional
area (m2)
Resistivity
(calculated)
%error
Table 3
Gauge Number
Diameter (cm)
20
0.08118
22
0.06429
24
0.05105
26
0.04049
28
0.02311
30
0.02548
Revised December 2011