What happens when light passes through two narrow slits instead of one? You cut a single slit in one piece of cardboard and two parallel slits in another. Then you shine a laser pointer through each card onto a white screen in a dark room.
With one slit, the light spreads into a bright band that fades at the edges. With two slits, the spreading light waves overlap and interfere with each other. This creates a pattern of alternating bright and dark bands on the screen. The pattern is three to four times wider than the single-slit result.
Hypothesis
The hypothesis is that the double slit experiment will prove that light has the properties of waveforms.
Laser light waves all travel in the same direction, which makes them ideal for revealing how light behaves as a wave. Shine a laser pointer through two narrow slits cut in cardboard and the spreading waves overlap on the other side. As a result, they interfere with each other — combining in some spots and canceling in others. The screen shows a pattern of alternating bright and dark bands that is three to four times wider than the single-slit result, proving that the synchronized waves can add or cancel depending on their alignment.
Light does not always travel in a straight line. When it passes through a narrow opening, it bends and spreads outward — and you can see this directly with a laser pointer and two sheets of cardboard. Cut two small parallel slits in one sheet, set up a whiteboard as a screen in a dark room, and shine the laser through. The light spreads well beyond the width of the slits. Where the spreading waves overlap and interfere, they create a pattern of alternating bright and dark bands that is three to four times wider than the single-slit result.
Shining a laser through two narrow slits produces a result that a single slit cannot. You cut one slit in a piece of cardboard and two parallel slits in another, then shine a laser pointer through each onto a white screen in a dark room. With one slit, the light spreads into a bright band that fades at the edges. With two slits, the spreading light waves overlap and interfere — combining in some spots and canceling in others. The result is a pattern of alternating bright and dark bands that is three to four times wider than the single-slit result.
Method & Materials
You will set up the experiment by cutting two small slits in a sheet of cardboard and placing it in front of a light source. You will then place a whiteboard at the back to act as the screen. You will then adjust the distance between the light source and the screen so that the diameter of the circle of light that falls on the slits is larger than the slits on the cardboard.
You will need a light source (for example, a laser pointer), two sheets of cardboards 100mm x 100mm in size, a paper cutter, a stack of newspapers, and a white board to act as the screen.
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The results of the experiment show that when light passed through the cardboard with only one slit, it was diffracted. When the test was repeated using the cardboard sheet with two slits, light leaving both the holes were diffracted. The diffracted light from the two slits met and "interfered", resulting in the interference pattern of dark and light bands on the whiteboard screen. This proves the wave properties of light.
Why do this project?
This science project is interesting and unique because it allows students to explore the dual nature of light and observe the wave-like behavior of light.
Also Consider
Experiment variations to consider include varying the size of the slits and putting pinholes into the cardboards in different locations.
Full project details
Additional information and source material for this project are available below.
