PASCO PS-2006 GLX Power Amplifier - Manual (Page 18)

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P S - 2 0 0 6 G L X P o w e r A m p l i f i e r S a m p l e E x p e r i m e n t s : O h m ’ s L a w a n d R e s i s t i v i t y
16
Ohm’s Law and Resistivity
In this experiment, the GLX makes a four-wire resistance measurement
of a length of wire. The Power Amplifier measures the current through
the wire, and a galvanometer sensor measures the voltage drop across it.
The galvanometer sensor is used (rather than the Power Amplifier’s
built-in voltage measurement) because is measures the voltage only
over the selected length of wire. The Power Amplifier, on the other
hand, registers the voltage at its output terminals. These quantities are
not equal, especially at high current when the voltage drop across the
output leads can be significant.
While a single measurement of voltage and current is sufficient to deter-
mine resistance using Ohm’s Law, a more precise method is to vary the
voltage and measure the changing current. On a plot of voltage versus
current, the slope of the best-fit line is equal to resistance.
Set-up
1. Set up a resistance apparatus or a simple length of wire as follows.
• Resistance apparatus:
a. Select a wire and install it in the apparatus.
b. Place the reference probe at 0 cm.
c. Place the slider probe at any point along the wire.
d. Use two patch cords to connect the power jacks of the
apparatus to the Power Amplifier.
e. Connect the galvanometer sensor to the reference and
slider probes of the apparatus.
• Length of wire
a. Use two alligator clips and two patch cords to connect the
Power Amplifier to the ends of the wire.
b. Use two other alligator clips to connect the galvanometer
sensor to two points along the length of the wire.
2. Connect the galvanometer sensor to the GLX.
Additional Equipment Part Number
Resistance Apparatus
or
a length of wire and four alligator
clip adapters
EM-8812
Galvanometer Sensor PS-2160
Patch Cords (2) SE-9750 or SE-9751
a
a
a
a
b
b
b
b
Figure 9: Resistance Apparatus (left)
or Length of Wire (right)
(a) to Power Amplifier
(b) to Galvanometer Sensor