®
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
6
Procedure
1.
Set the power supply to 5 V (constant DC) and simultaneously start recording in
DataStudio. Watch the graph of “far” temperatures and allow them to increase for
about 5 minutes. Stop recording.
2.
Set the power supply voltage to zero. Remove the insulators to allow the bars to
cool.
Analysis
1.
Look at the final temperature measured by the “far” thermistor of each bar.
Which material is the best conductor? Which is the worst? Is there a difference
between the two brass bars?
2.
Create a graph showing data from both thermistors in the wide brass bar (T1 and
T2). Zoom in on the area of the graph where the temperatures start to increase.
Notice that the temperature at the close thermistor (T2) starts to increase before
the temperature at the far thermistor (T1). Measure this time difference.
3.
Calculate the speed of the heat pulse down the brass bar. At this speed, how long
would it take for the pulse to travel the length of the bar?
4.
In DataStudio, create a calculation for the temperature differ-
ence (
∆
T) between the close and far thermistors in the wide
brass bar. Create similar calculations for the other three bars
(be sure to subtract the “far” temperature from the “close”
temperature). Display all four calculations in a graph.
Which bar has the largest
∆
T? Which bar has the smallest?
What is the correlation between
∆
T and how good a
conductor each material is?
5.
Why does
∆
T peak and then decrease? Why does this peak occur at different
times for the four bars?
6.
Notice that
∆
T in each bar approaches a final equilibrium value. Estimate this
final value for each bar.
7.
The rate of heat flow (
∆
Q
/∆
t, in joules per second) is given by
where k is the thermal conductivity of the material, A is the cross-sectional area
of the bar, and x is the distance between the thermistors.
See page 4 for the conductivities of brass, aluminum, and stainless steel. Measure
the dimensions of the bars. Calculate the final heat flow rate in each bar.
8.
Which bar has the highest heat flow rate? Is there a correlation between
∆
T and
heat flow rate? Why is the heat flow lower in the narrow brass bar than in the
wide one?
Further Study
Repeat the previous experiment with the switch set to COOL. Which direction does
heat flow in this case?
1
To cool the bars faster,
you can set the switch to
COOL and apply 5 volts
for a few minutes; then
wait a few more minutes
with the apparatus
un-powered for the bars
to come to equilibrium.
Q
∆
t
∆
--------
kA T
∆
x
--------------
=
