PASCO OS-8542 BLACK BODY LIGHT SOURCE - Manual (Page 17)

012–07105B Black Body Instruction Manual
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Teacher’s Guide
Notes:
1. See the Operational Notes section of this manual for important setup reminders.
2. Before beginning the experiment, have students do the following:
a) Set the collimating and aperture slits.
b) Check the position of the prism.
c) Ensure the cables from the rotary motion sensor are properly inserted into ScienceWorkshop.
d) Check to see that the black body light is turned on and is emitting steady light.
Students can turn the bulb on from the Signal Generator box in DataStudio. If the bulb does not turn on or
emits intermittent bursts of light, see the Troubleshooting section of this manual.
Calibration:
Init Angle: 76.8 degrees (1.33 rads)
Ratio of plate to pin radius: 59.740
Procedure: Scanning a Spectrum
Spectrum Color
(deg) θ(rads) n
Red 58 1.01 1.714 746
Yellow 59 1.03 1.717 705
Green 60 1.05 1.732 569
Blue 61 1.06 1.741 517
Violet 62 1.08 1.749 481
Sample Data
Theory of the Black Body Experiment
An incandescent light source that emits light through a small cavity is a “perfect emitter.” By definition, a perfect
light emittter is one that emits light rays throughout an infinite number of frequencies in the visible and invisible
electromagnetic spectrum. When light from the black body is cast through a prism, the observed spectrum is
continuous, and no overlapping of the spectral lines occurs.
In this experiment, parallel light rays travel through the collimating lens, which allows the light rays to remain
parallel. Passing through the prism, the light rays refract and project in front of the aperture slit over the light
sensor. The light sensor detects and records the light intensity as voltage.
Unlike other light sources, changes in light intensity from an incandescent black body is solely dependent on
temperature. Increasing the temperature of the black body light source increases the light intensity. For any given
temperature, there appears to be an optimal wavelength for reaching a maximum light intensity.
The angle of the emitted light depends upon the refraction index of the prism and the wavelength of the rays.
Shorter wavelengths show more “bend” than longer wavelengths and therefore exihibit higher indices of refraction.
λ