PASCO TD-8580A Thermal Cavity - Manual (Page 4)

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Thermal Cavity Suggested Experiments
4
4. Open the configuration file IR_vs_Temp.ds.
Procedure
Start with the cube below 40 °C.
1. Click Start.
2. Apply 10 V to the apparatus.
When the cube reaches 40 °C, data recording will automatically begin.
3. After the cube has reached 90 °C, click Stop. (If the cube reaches 100 °C, data
recording will automatically stop.)
4. Turn off power to the apparatus.
Analysis
1. According to your data, how is measured IR intensity related to cube tempera-
ture?
2. The Stefan-Boltzmann law states that a surface’s radiant intensity, I, is related to
its absolute temperature, T, by
where ε is the emissivity of the surface, and σ is the Stefan-Boltzmann constant.
The measurement of I made by the IR sensor is proportional to the net power
exchange, P
net
, between the surface and the sensor. The net power is related to
the surface’s absolute temperature, T, and the sensor’s own absolute temperature,
T
0
, by
where k is a constant related to the geometry of the surface and the sensor. 2
Observe the graphs of I versus T and I versus T 4 . Does your data appear to
support this relationship?
3. Repeat the experiment with the polished and white surfaces of the cube. How do
the emissivities of the black, polished, and white surfaces compare?
I ε σ T
4
=
σ=
5.670 × 10 -8 W/m 2 ·K 4
P
net
ε k σ T
4
T
0
4
–
( )
=
2 The PASPORT IR sen-
sor makes a direct mea-
surement of T
0
, which
you can use in your anal-
ysis.