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Teacher’s guide (continued) – PASCO OS-8542 BLACK BODY LIGHT SOURCE User Manual

Page 19

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012–07105B

Black Body Instruction Manual

15

Teacher’s Guide (Continued)

Answers to Questions from Page 14

1) The intensity of the light is related to the temperature of the bulb by I

αT

4

. The higher the bulb temperature, the

higher the intensity that the light ray becomes. The peak wavelength is shifted to higher frequencies (and
shorter wavelengths) at higher temperatures.

2) A prism spectrophotometer has two advantages over a grating spectrophotometer: a) it eliminates overlap of

orders observed with a grating. (When a grating is used, second order visible wavelengths orverlap first order
infrared wavelengths.), and b) the spectrum is brighter because it does not spread over several orders or in
both directions.

3) The spectral lines converge at a point in front of the light sensor. However, beyond the light sensor, light rays

diverge. The light rays do not overlap.

4) The collimating lens allows the light rays to travel parallel to one another before passing through the prism.

The parallel lines serve as a reference to compare to when measuring the angle of refraction.

I

f you remove the collimating lens, the waves will refract and reflect off of the various objects in the room

before reaching the prism. These waves would bend at various angles, and would make it difficult to
determine a reference line for the path of light travel through the prism. You would not be able to obtain an
accurate measurement of the refracted angle.

5) The angle of a wave is directly related to its ability to refract. The larger the angle, the greater the “bend” or

refraction, and the shorter the resulting wavelength. For any given temperature, there appears to be an
optimal wavelength for reaching a maximum light intensity.

6) Unlike other light sources, changes in light intensity from an incandescent black body is solely dependent on

temperature. The spectra of an incandescent light source are continuous and rainbow colored. Gas light
sources display discrete spectra.

7) The graphs display waves between 400-700 nm because the high sensitivity light sensor detects light in the

visible region of the electromagnetic spectrum. With the high sensitivity light sensor, you will not be able to
observe waves of infrared light, which are typically greater than 750 nm and lie in the invisible region of
the electromagnetic spectrum.