PASCO OS-8542 BLACK BODY LIGHT SOURCE - Manual (Page 14)

Black Body Instruction Manual 012-07105B
10
A. Black Body Spectrum: Scanning Nested Curves from Black Bodies of Different Temperatures
Note: Before running the experiment, perform the rotary motion sensor calibration, as described in
the “Calibration” section on page 9. Enter this calibration as “Ratio” into the DataStudio calculator,
and click the Accept button.
1. Rotate the light sensor arm until it hits the stop against the angle indicator on the circular table.
Note: Before proceeding, the black body light source must be turned on and emitting light.
If not, click the On button in DataStudio’s Signal Generator dialog box.
2. Block the light source by placing your hand between the collimating slits and the collimating
lens. While the light is blocked, press the tare button on the light sensor to zero the sensor.
3. Remove your hand to unblock the light and start recording data on the computer. Click the Start
button in the DataStudio setup window, and slowly rotate the light sensor arm through the spectrum.
Experiment
4. Stop recording data. The initial angle (when the
stop is against the angle indicator) is required to
calculate the wavelength.
5. In DataStudio, make a graph of intensity vs. angular
position. Measure the angle to the white light that
passes directly through the spectrophotometer and
under the prism. This angle is subtracted from all
angles, so that all angles are referenced from the
reference line (the parallel beams that travel in a
straight line through the spectrophotometer).
6. Enter the intial angle as “Init” into the wavelength
calculation in the DataStudio calculator.
Figure 10: Measuring the Angle of the
Refracted Light (Using DataStudio)
Initial angle Angle to white light
4. After you have scanned through the spectrum, stop rotating the arm, continue recording and
push the tare button again. Place your hand between the collimating slits and the collimating lens
to block the light and return the light sensor arm to its original position against the stop. Block
ing the light during this time causes the return scan to be below the axis of the graph, so it does
not trace back over the black body data.
5. a) Change the temperature of the bulb by changing the voltage applied to the bulb. You get tem-
perature from current and voltage, as shown by
Temp.(K) = 300 + ((voltage/current)/0.84 - 1/.0045).
b) For each temperature, determine the maximum peak (
λ
max
) of the wavelength. Use the Wien
displacement law, where
λ
max
T =2898
μm ⋅ K, to calculate the λ
max
.