How to Perform Young's Double Slit Experiment

Before 1801, the theory was that light was made of tiny bullet-like particles because it seemed to travel in a straight beam. Young's double slit experiment proves that light travels in waves, and that these waves are transverse rather than longitudinal. You can perform his experiment by following these steps.

Instructions

Difficulty: Easy

Things You’ll Need:

• Thin solid plate with two slits in it
• Light source
• 3 photographic plates

Performing the Experiment

1. Set up your light source. A desk lamp will do for an informal experiment. For a more rigorous experiment, use a light source that has a constant knowable output. Where you set it up is only important in relation to the other pieces, so you may need to adjust the position as you go.
2. Position the slitted plate so that the slits are vertical and parallel to each other and far enough away from the light source that both slits receive the same amount of light.
3. Place the photographic plate at a distance so that it receives light through both slits equally when neither one is obstructed. If you have any doubt, placing it the distance from the plate that the light source is should work. Make sure that it's on the opposite side of the slitted plate from the light source.
4. Prepare the photographic plate by removing any covering or obstructions between it and the slitted plate.
5. Activate the light source. Wait a few moments. Deactivate the light source.
6. Replace the photographic plate and obstruct a slit. Repeat Steps 3 through 5.

Analyzing the Data

7. Develop the photographic plates. If the results are intended for professional use, consider taking them to a professional developer.
8. Look at the pattern. If the experiment was performed well, it should look like the results found at the University of Colorado Physics 2000 website.
9. Consider what this means about the nature of light, particularly with regards to wave versus particle travel. Light particles would result in a one-sided image when the light was blocked, but waves would create a much larger image.

Tips & Warnings

• In order to prevent the plate from being overexposed, minimize the external light in the area and keep the photographic plate covered until you're ready to perform the experiment.