PASCO EM-8812 Resistance Apparatus User Manual
Page 10
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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 2 : R e s i s ta n c e v e r s u s L e n g th
10
7.
Set up the other galvanometer to measure current (I):
a.
Use the BNC-to-banana jack adapter to connect the 0.1
Ω resistor across the
terminals of the galvanometer.
b.
Press the tare button on the galvanometer.
c.
Insert the resistor into the circuit in series with the power supply and appara-
tus.
d.
Turn the power supply’s function knob to Constant DC (
).
e.
On the power supply, press
to display current. Turn the
Fine knob slowly to set the current to about 1 A. Note the exact
current on the display.
f.
Collect a few seconds’ worth of test data. Note the average
voltage measured by the galvanometer (make sure you are
looking at the current-sensing galvanometer, it should read
about 100 mV).
g.
Use
the current (displayed on the power supply), the voltage
(measured by the galvanometer), and Ohm’s law to calculate
the resistance of the resistor (it will be close to 100 m
Ω).
h.
Enter this calculation in the DataStudio or GLX calculator:
current = voltage/100.0
with your calculated resistance (in m
Ω) in place of the
“100.0”. Define “voltage” as the voltage (in mV) measured by
the galvanometer (again, make sure it is the current-sensing
galvanometer). In this way, current is measured in amps.
8.
Program the power supply for a 0 to 1 A ramp:
a.
Turn the power supply’s function knob to Constant DC (
).
b.
Press
to display current (if it is not already displayed). Turn the Fine
knob slowly to set the current to about 1 A.
c.
Press
again to display voltage and note this voltage.
d.
Turn the function knob to Ramp (
). Turn the Coarse and Fine knobs to
set the height of the ramp (shown on the display) to the voltage that you
noted in step c.
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.
Current calculation in DataStudio (top)
and on the GLX (bottom)