PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the wavelength of a light source following Young's experiment.

INTRODUCTION:
In the early 1800's, Thomas Young conducted his experiment. He allowed light to pass through a slit in a barrier so it expanded out in wave fronts from that slit as a light source. That light, in turn, passed through a pair of slits in another barrier. Each slit, in turn, diffracted the light as if they were also individual sources of light. The light projected on an observation screen.

There are two possible results of this experiment

1) Particle interpretation: If light exists as particles, the intensity of both slits will be the sum of the intensity from the individual slits, resulting in two bright bars.

2) Wave interpretation: If light exists as waves, the light waves will have interference under the principle of superposition, creating bands of light (constructive interference) and dark (destructive interference).

When the experiment was conducted, the light waves did indeed show these interference patterns supporting the wave interpretation of light. This lab follows the original experiment with the exception that an artificial light source is used.

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Show from left to right, the light source, slit holder and observation screen. A monochromatic light is generated in the light source, passes through two slits in the slit holder and is then projected on the screen.

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The distance between light bars on the interference pattern, is measured by a shortened meter stick.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

2) Click on the "Special" button and adjust the background until it is black. Viewing of this lab must be done in a darkened room.

3) Turn on the light source by clicking on the side switch. This light source will produce a light of only one wavelength and is thus monochromatic in nature.

4) Drag the slit holder to the right and left and note the effect on the interference pattern on the screen. Drag the slit holder to the far left and drop it.

5) Drag and position the measuring tape so that its left side lines up with the center of the slit holder. Click on the top button of the tape. The tape button should turn red indicating that the body of the tape measure can be dragged to the right exposing the metered tape. Pull the body of the tape measure over past the screen. Click on the tape button once more and then the entire tape measure can be moved. Record the distance from the center of the slit holder to the face of the screen remembering that the tape measure is graduated in meters.

6) Position the meter stick, under the close-up of the screen, and measure the distance from the central bright bar to the next bar on either side. This measurement will be in cm so convert to meters and record.

7) Drag the slit holder to the right 1/3 the distance to the screen. Measure the distance from slit holder to screen and the distance from the central bright bar to the next. Record.

8) Drag the slit holder to the right 2/3 the distance to the screen. Measure the distance from slit holder to screen and the distance from the central bright bar to the next. Record.

Note that the distance between slits on the slit holder is a constant 5.00 E-5 meters and has been entered into the data sheet for you.

9) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.