PASCO EM-8812 Resistance Apparatus - Manual (Page 12)

®
R e s i s ta n c e A p p a r a t u s E x p e r i m e n t 3 : V o l ta g e v e r s u s L e n g th
12
Experiment 3: Voltage versus Length
Theory
The resistance (R) of a wire depends on its dimensions and the resistivity (
ρ) of the
material. For a wire of cross-section area (A) and length ( ),
(eq. 3-1)
If a current (I) is flowing through the wire, the voltage drop (across the measured
length) is given by Ohm’s law:
(eq. 3-2)
Combining these two equations yields
(eq. 3-3)
Thus, the slope of a V versus graph is .
Setup
1. Measure* diameter of the four brass wires and calculate their cross sectional
areas.
2. Install the smallest brass wire in the apparatus (see “Wire Installation” on
page 5).
3. Position the reference probe at the 0 cm mark and the slider probe at the 24 cm
mark.
4. Connect the power supply to the power jacks of the apparatus so that current will
flow from right to left through the wire. Put the multimeter in series with the
power supply to measure the current. Adjust the regulated current to about 1 A.
(The current-regulated power supply ensures that the current will remain con-
stant.)
5. Connect the galvanometer to the reference (-) and slider (+) probes of the appara-
tus.
6. Connect the galvanometer to your PASPORT interface. If you are using a com-
puter, start DataStudio.
Equipment Required Part Number
Resistance Apparatus with wire set EM-8812
Current-regulated Power Supply SE-9720A
Patch Cords (4mm banana plug) SE-7123
Galvanometer Sensor PS-2160
PASPORT Interface See PASCO catalog
Multimeter (to measure current) SE-9786A
Micrometer (optional) SE-7337
R
ρ
A
--- =
V IR =
V
ρI
A
----- =
ρI A ⁄
*If you do not have a
micrometer, use these
values of diameter:
0.13 cm
0.10 cm
0.081 cm
0.051 cm