®
M o d e l N o . T D - 8 5 1 3
E x p e r i m e n t # 1 : H e a t C o n d u c t i o n
7
B. Heat Pulse
Set-up
1.
Set the switch to HEAT and place the insulators over the bars.
2.
In DataStudio, set the sampling rate of the Temperature Array to 2 Hz. Set up a
graph display to show the temperatures measured by both thermistors in the wide
brass bar (T1 and T2).
3.
Collect a test run of data to make sure that all four bars are all at room tempera-
ture. Delete the data.
Procedure
1.
Set the power supply to 5 volts (constant DC) and start recording in DataStudio.
Wait until the “close” temperature (measured by T2) reaches about 40 °C.
2.
Change the switch to the COOL position and start timing with a clock or stop-
watch. Change the switch every 30 seconds. In this way the end of the bar is
alternately heated and cooled with a period of 60 s.
3.
Continue for several minutes until the temperature wave at each thermistor has
stabilized with a constant amplitude.
4.
Stop data recording and set the power supply to 0 V.
Analysis
1.
Observe the shape of the two waves (it helps to zoom in on the last few cycles).
What is the shape of the wave that you applied to the bar by switching between
heating and cooling? What is the shape of this wave when it reaches the close
thermistor (T2)? How has it changed when it reaches the far thermistor (T1)?
2.
Notice that there is a time lag between the two waves. What causes this? Measure
the time lag. How is the time lag related to the distance between the thermistors?
3.
Why is there an amplitude change between the two waves? Are these really two
different waves?
4.
Create a new graph showing data collected by the thermistors in the aluminum
bar (T5 and T6). Repeat analysis steps 1 through 3 for the aluminum bar.
5.
Compare the shape of the waves in the aluminum and brass bars. Why are they
different? Compare the amplitude of the waves. Which material is the better con-
ductor?
6.
Compare the time lags in the aluminum and brass bars? What does this tell you
about the speed of the pulse in each bar?
C. Heat Waves
Theory
In this part, the power supply will apply a triangle wave voltage to the Peltier device.
This heating and cooling of one end of each bar causes a thermal wave to travel down
the bar. The wave on each bar is measured by two thermistors. You will investigate
the relationship between wave speed, period, and wavelength.
2
You can decrease the
wait time by applying a
higher voltage (8 V), but
reduce the voltage back
to 5 V before the temper-
ature reaches 40
o
C.
3
If you are going to do
part C of this lab, set the
power supply now. This
will allow the system to
come to equilibrium while
you perform the follow-
ing analysis. See the
Set-up section for part C
below.
