PASCO TD-8555 THERMAL RADIATION SYSTEM - Manual (Page 21)

17
012-04695D Thermal Radiation System
Experiment 4: Stefan-Boltzmann Law (low temperature)
1
2
3 4 5
6
7
8
LOW HIGH
CAUTION: HOT! CA
UT
IO N
HO
T!
TH ER MIS TO R
Mo del TD -85 54A
(LE SL IE'S CU BE )
100W
BULB
MAX.
ON
OFF
Figure 4.1 Equipment Setup
Millivoltmeter
Ohmmeter
EQUIPMENT NEEDED:
— Radiation Sensor — Thermal Radiation Cube
— Millivoltmeter — Ohmmeter.
Introduction
In experiment 3, you investigated the Stefan-Boltzmann Law (R
rad
= sT 4 ) for the high
temperatures attained by an incandescent filament. At those high temperatures (approxi-
mately 1,000 to 3,000 K), the ambient temperature is small enough that it can be neglected
in the analysis. In this experiment you will investigate the Stefan-Boltzmann relationship at
much lower temperatures using the Thermal Radiation Cube. At these lower temperatures,
the ambient temperature can not be ignored.
If the detector in the Radiation Sensor were operating at absolute zero temperature, it would
produce a voltage directly proportional to the intensity of the radiation that strikes it. How-
ever, the detector is not at absolute zero temperature so it is also radiating thermal energy.
According to the Stefan-Boltzmann
law, it radiates at a rate, R
det
=
sT
det
4 . The voltage produced by the
sensor is proportional to the radia-
tion striking the detector minus the
radiation leaving it. Mathemati-
cally, the sensor voltage is propor-
tional to R
net
= R
rad
– R
det
= s(T 4 -
T
det
4 ). As long as you are careful to
shield the Radiation Sensor from
the Radiation Cube when measure-
ments are not being taken, T
det
will
be very close to room temperature
(T
rm
).
Procedure
① Set up the equipment as shown in
Figure 4.1. The Radiation Sensor should be pointed directly at the center of one of the
better radiating surfaces of the cube (the black or white surface). The face of the Sensor
should be parallel with the surface of the cube and about 3 to 4 cm away.
② With the Thermal Radiation Cube off, measure R
rm
, the resistance of the thermistor at room
temperature. Enter this data in the space on the following page.
③ Shield the sensor from the cube using the reflecting heat shield, with the reflective side of
the shield facing the cube.
④ Turn on the Radiation Cube and set the power switch to 10.
⑤ When the thermistor resistance indicates that the temperature is about 12 C° above room
temperature, turn the power down so the temperature is changing slowly. Read and record
R, the ohmmeter reading, and Rad, the millivoltmeter reading. The readings should be
taken as nearly simultaneously as possible while briefly removing the heat shield. Record
these values in Table 4.1.
Heat Shield
(reflective side
toward cube)