PASCO TD-8555 THERMAL RADIATION SYSTEM - Manual (Page 7)

3
012-04695D Thermal Radiation System
TD-8555
STEFAN-BOLTZMAN
LAMP
CAUTION
13 VDC MAX LAMP VOLTAGE
FOR MAXIMUM ACCURACY,
MEASURE VOLTAGE AT
BINDING POSTS
USE NO.1196 BULB
Stefan-Boltzmann Lamp
For large temperature differences, therefore, deter-
mine the temperature of the tungsten filament as
follows:
① Accurately measure the resistance (R
ref
) of the tung-
sten filament at room temperature (about 300 °K).
Accuracy is important here. A small error in R
ref
will result in a large error in your result for the fila-
ment temperature.
② When the filament is hot, measure the voltage and
current into the filament and divide the voltage by
the current to measure the resistance (R
T
).
③ Divide R
T
by R
ref
to obtain the relative resistance
(R
T
/R
ref
).
④ Using your measured value for the relative resistiv-
ity of the filament at temperature T, use Table 2 on
the following page, or the associated graph, to de-
termine the temperature of the filament.
IMPORTANT: The voltage into the lamp
should NEVER exceed 13 V. Higher voltages
will burn out the filament.
The TD-8555 Stefan-Boltzmann Lamp (Figure 3) is a
high temperature source of thermal radiation. The
lamp can be used for high temperature investigations
of the Stefan-Boltzmann Law. The high temperature
simplifies the analysis because the fourth power of the
ambient temperature is negligibly small compared to
the fourth power of the high temperature of the lamp
filament (see Experiments 3 and 4). When properly
oriented, the filament also provides a good approxima-
tion to a point source of thermal radiation. It therefore
works well for investigations into the inverse square
law.
By adjusting the power into the lamp (13 Volts max, 2
A min, 3 A max), filament temperatures up to approxi-
mately 3,000 °C can be obtained. The filament
temperature is determined by carefully measuring the
voltage and current into the lamp. The voltage divided
by the current gives the resistance of the filament.
Equipment Recommended
AC/DC LV Power Supply (SF-9584) or equivalent
capable of 13 V @ 3 A max
For small temperature changes, the temperature of
the tungsten filament can be calculated using a, the
temperature coefficient of resistivity for the filament:
where,
T = Temperature
R = Resistance at temperature T
T
ref
= Reference temperature (usually room temp.)
R
ref
= Resistance at temperature T
ref
a = Temperature coefficient of resistivity for the
filament (
α
= 4.5 x 10 -3 K -1 for tungsten)
For large temperature differences, however, a is not
constant and the above equation is not accurate.
T = + T
ref
R - R
ref
aR
ref
REPLACEMENT BULB: GE Lamp No. 1196,
available at most auto parts stores.
ä NOTE: When replacing the bulb, the leads
should be soldered to minimize resistance.
PASCO scientific
Banana Connectors:
Connect to Power
Supply – 13 V MAX,
(2 A min, 3 A max)
Figure 3 Stefan-Boltzmann Lamp