Pasco OS-8500 INTRODUCTORY OPTICS SYSTEM Manuel d'utilisateur télécharger pdf (Page 30)

Introductory Optics System 012-02744K

Attach the Diffraction Plate to the other side of the Component Holder, as shown. Center pattern D, with the

slits vertical, in the aperture of the Slit Mask. Look through the slits. By centering your eye so that you look

through both the slits and the window of the Diffraction Plate, you should be able to see clearly both the

interference pattern and the illuminated scale on the Diffraction Scale.

➤➤

➤NOTE:

In this experiment, you look through the narrow slits at the light source, and the diffraction

pattern is formed directly on the retina of your eye. You then see this diffraction pattern superimposed

on your view of the illuminated diffraction scale. The geometry is therefore slightly more complicated

than it would be if the pattern were projected onto a screen, as in most textbook examples. (A very

strong light source, such as a laser, is required in order to project a sharp image of a diffraction pattern

onto a screen.)

The essential geometry of the experiment is shown in Figure 9.2. At the zeroth maxima, light rays from

slits A and B have traveled the same distance from the slits to your eye, so they are in phase and interfere

constructively on your retina. At the first order maxima (to the left of the viewer) light from slit B has

traveled one wavelength farther than light from slit A, so the rays are again in phase, and constructive

interference occurs at this position as well.

At the nth order maxima, the light from slit B has traveled n wavelengths farther than the light from slit

A, so again, constructive interference occurs. In the diagram, the line AC is constructed perpendicular to

the line PB. Since the slits are very close together (in the experiment, not the diagram), lines AP and BP

are nearly parallel. Therefore, to a very close approximation, AP = CP. This means that, for constructive

interference to occur at P, it must be true that BC = nλ.

From right triangle ACB, it can be seen that BC = AB sin θ, where A is the distance between the two slits

on the Diffraction Plate. Therefore, AB sin θ = nλ. (The spacing between the slits, AB, is listed in the

Equipment section of this manual.) Therefore, you need only measure the value of θ for a particular

value of n to determine the wavelength of light.

To measure θ, notice that the dotted lines in the illustration show a projection of the interference pattern onto the

Diffraction Scale (as it appears when looking through the slits). Notice that

θ´ = arctan X/L. It can also be shown from the diagram that, if BP is parallel to AP as we have already

assumed, then θ´ = θ. Therefore, θ = arctan X/L; and AB sin (arctan X/L) = nλ.

Looking through the pair of slits (pattern D) at the Light Source filament, make measurements to fill in Table

9.1. Alternately place the Red, Green, and Blue color filters over the Light Source aperture to make the meas-

urements for the different colors of light. If you have time, make measurements with the other two-slit patterns

as well (patterns E and F on the Diffraction Plate). Perform the calculations shown to determine the wavelength

of Red, Green, and Blue Light.

Additional Questions

➀ Assume, in the diagram showing the geometry of the experiment, that AP and BP are parallel.

Show that θ = θ´.

➁ Suppose the space between the slits was smaller than the wavelength of light you were trying to measure.

How many orders of maxima would you expect to see?

()

split

spacing

( )

Data Calculations

Color n AB X L sin (arctan X/L) = λ

Red

Green

Blue

Table 9.1 Data and Calculations

1 2 ... 25 26 27 28 29 30 31 32 33 34 35 ... 74 75

Commentaires sur ces manuels

Pas de commentaire

Pasco OS-8500 INTRODUCTORY OPTICS SYSTEM Manuel d'utilisateur Page 30

Commentaires sur ces manuels

Produits connexes et manuels pour Équipement Pasco OS-8500 INTRODUCTORY OPTICS SYSTEM