PASCO TD-8555 THERMAL RADIATION SYSTEM - Manual (Page 24)

Thermal Radiation System 012-04695D
20
Notes on Questions
① The graph of Radiation versus 1/x 2
is more linear,
but not over the entire range. There is a distinct
falloff in intensity at the nearer distances, due to the
non-point characteristics of the lamp. (A graph of
Radiation versus 1/x
2
using only data points from
10cm or more is nearly linear.)
② If we use data from distances that are large com-
pared to the size of the lamp filament—so that the
filament is effectively a “point”—then this data sup-
ports the hypothesis.
③ The Stefan-Boltzmann Lamp is not truly a point
source. If it were not, then there would be a falloff
in light level for measurements taken close to the
lamp. This falloff can be seen in our data.
Suggestion:
The largest part of the error in this lab is due to the
non-point nature of the Stefan-Boltzmann Lamp.
You can approximate a much better “point” source
with a laser and a converging lens.
"P o int" S o u rce
L as er
For best results, use a short-focal-length lens and
make sure that the sensor is always completely
within the beam.
Notes on Questions
① A power regression of our data shows a power of
4.36. However, an analysis of only those points
with temperature greater than 1500° shows a power
of 4.01. This inaccuracy in the low-temperature
points is due to absorbtion of the infrared by the
glass lamp bulb. (See experiment 1) This absorbtion
is more significant at the lower temperatures, where
the infrared makes up a larger percentage of the en-
tire output.
X
X
X
X
X
X
X
X
X
X
X
X
0.1
1
10
100
100 1000 10000
Radiation sensor Voltage
Temperature (K)
f(x) = 5.521363E-14 * (x^4.363707E+0 )
R^2 = 9.979700E-1
f(x) = 8.141230E-13 * (x^4.006331E+0 )
R^2 = 9.974766E-1
First fit uses all data points,
second uses only those 1500K or higher.
Experiment 3: Stefan-Boltzmann Law (at high temperatures)
Notes on Procedure
Part 1
③ Between readings, place the insulating material be-
tween the lamp and the sensor. For best results use
both sheets, with the aluminum sides facing away
from each other. Remove the sheets for only
enough time to take each measurement.
Calculations
③/④
1
1
1
1
1
1
1
1
1
1
1
1
0
2
4
6
8
10
12
14
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Radiation Sensor Voltage
Temperature (K)
f(x) = 5.521363E-14 * (x^4.363707E+0 )
R^2 = 9.979700E-1