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H e a t C o n d u c t i o n Ap p a r a t u s
E x p e r im e n t # 1 : H e a t C o n d u c t i o n
8
Set-up
1.
Set the switch to COOL.
2.
Place the insulators on the bars.
3.
Set the power supply to output an 8 V positive triangle wave with a 50 s period,
as shown in the diagram. See the PI-9877 DC Power Supply manual for detailed
instructions.
4.
In DataStudio, set the sampling rate to 2 Hz. Create a graph to show data col-
lected by both thermistors in the wide brass bar (T1 and T2).
5.
Start recording data. Wait for several minutes until the thermal wave at each ther-
mistor has stabilized with a constant amplitude. Stop recording data and delete
the data run.
Procedure
Start recording data again. After two full cycles, stop recording.
Analysis
1.
Measure the time lag between the wave measured by the “close” and “far” ther-
mistors.
2.
Calculate the speed (
V
) of the wave using the distance between the thermistors
and the time lag between the waves.
3.
Calculate the frequency (f) of the wave in Hz.
4.
The speed of any wave is related to its frequency and wavelength (
λ
) by
Calculate the wavelength of this wave. How does
λ
compare to the length of the
entire bar?
5.
Create another graph showing temperatures measured in the aluminum bar.
Repeat analysis steps 1 through 4. Do the same for the narrow brass bar and the
stainless steel bar.
Questions
1.
Is the wave speed different in each material? Which has the highest speed? How
is the wave speed related to the conductivity of the material?
2.
Notice the decrease in amplitude (attenuation) of the wave measured at the far
thermistor compared to the close thermistor. How is this related to the material
and the conductivity? Which material has the most attenuation.
Further Study
Repeat the experiment for a wave with a period of 100 Hz. How are the wave speed,
wavelength, and attenuation affected by the frequency of the wave?
8 V
0 V
50 s
Power Supply Settings:
Max. Voltage
8 V
Min. Voltage
0 V
Period
50 s
Auto-repeat
−
0
4
If you are going to do
the Further Study part of
this section, change the
period of the triangle
wave to 100 s now and
allow the system stabilize
while you do the following
analysis.
V
λ
f
=
