How to Set Up a Double Slit Experiment
The double slit experiment demonstrates the wave properties of light. The two slits divide light into two wave centers that interfere with each other. Constructive interference is the term used when the crests of waves complement each other, causing bright vertical bands of light. Destructive interference is when the troughs from one wave source cancel out the crests from another, causing dark bands. The resulting interference pattern appears as a series of alternating dark and light vertical bands.
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Things You'll Need
- Paper
- Black felt-tip marker
- Ruler
- Camera
- Black and white film
- 2 clothespins
- 3 Styrofoam cups
- Tape
- Laser pointer
Instructions
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1
Fold a piece of paper in half from top to bottom to make a crease through the middle. After opening it, draw two parallel lines with a black marker and ruler from side to side where you made the crease. Make the distance between these lines 1/8 inch.
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2
Turn the paper 90 degrees and take a picture of it with black and white film. Once developed, the negative will appear black with two narrow white slits. It's important that the width of both of these slits together be narrower than the width of your laser's beam.
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3
Secure the negative with two clothespins, one on either side of your slit image. These will serve as legs to hold the negative upright in front of the laser, so the clothespins need to be on the same side, perpendicular to the negative's length.
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4
Cut around the circumference of two Styrofoam cups 3/4 inch from the bottom. These bottoms will be the bases for giving the clothespins more stability when standing upright, so turn the Styrofoam bases upside down and puncture them through the center with the clothespins. Tape the clothespins to the bases to give them more stability as they hold the negative in an upright position.
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Turn a third Styrofoam cup upside down, and mark the point that is at the same height as the center of your slit image. Do the same on the opposite side of the cup. These points correspond to the center of your laser, so with these center points, cut two holes big enough to slide your laser into place. When it's inserted, the laser should be horizontal at the right height to shine through the center of the slit image.
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6
Position the laser pointing at a wall four feet away. Place the negative with its clothespin stand in line with the laser's beam. Adjust it so that the beam passes through the slits. With all the other lights in the room turned down, a series of vertical lines should appear on the wall. This is the interference pattern, demonstrating light's wavelike properties.
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Tips & Warnings
The double slit experiment only works with coherent light, which is light whose photons have a common wavelength in phase with each other. Because of this, substituting a flashlight for the laser won't work.
Never shine a laser into anyone's eyes.
References
- Photo Credit Hemera Technologies/AbleStock.com/Getty Images
