PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM - Manual (Page 45)

012-02744K Introductory Optics System
®
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EQUIPMENT NEEDED:
-Optics Bench -Light Source
-Component Holders (2) -Variable Aperture
-Diffraction Plate -Slit Mask
-Color Filter (any color) -Black Construction Paper
-pin.
Experiment 17: General Diffraction
Figure 17.1 Equipment Setup
Introduction
The simplest diffraction patterns are produced by narrow slits. However, any aperture, or collection of
apertures, will produce a diffraction pattern if the dimensions of the apertures are of the same order of
magnitude as the wavelength of visible light.
The diffraction pattern created by a particular aperture can be determined quantitatively using Huygen’s
principle. Simply treat each aperture as a collection of point sources of light (small, closely packed
points will give the best approximation of the diffraction pattern). At any position on your viewing
screen, determine the phase of the light contributed by each point on the aperture. Finally, use the
superposition principle to sum the contributions from all the points on the aperture.
Of course, you must perform this same calculation for each point on your viewing screen to determine
the complete diffraction pattern—a time consuming task. In this experiment the approach will be more
qualitative. You will use your knowledge of diffraction patterns formed by slits to understand the
patterns formed by more complicated apertures.
Procedure
Setup the equipment as shown in Figure 17.1. Begin with the Variable Aperture fully open. Looking
through the Diffraction Plate at the Light Source filament, examine the diffraction patterns formed by
Patterns H, I, and J.
While looking through Pattern H, slowly close the Variable Aperture. Repeat this with Patterns I and J.
➀ What effect does aperture size have on the clarity of the diffraction patterns?
➁ What affect does aperture size have on the brightness of the diffraction patterns?
Adjust the Variable Aperture to maximize the brightness and clarity of the pattern. Place a color filter
over the Light Source Aperture.
➂ In what way does the color filter simplify the diffraction patterns that are formed?
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DI FF RA CT IO N P LA TE
A B C D
E
DIF FR AC TIO N P LAT E
J I H
G F