Internet version [Naruhodo no Mori] Vol.36

by Yumiko Mori

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Vol. 36     January 15th, 1998

Projecting Spectrum

Home science experiments for mothers of elementary school children

Tae: "It's pretty. We can see red, yellow. green and blue colors."
Mom: "Especially the red color is beautiful."
Tae: "Let Satoshi see this spectrum!"

Satoshi (4 year old) and his older brother, Toshi, came over.
Toshi: "What are you doing?"
Tae: "We are projecting a spectrum."
Toshi: "I know what you are doing. Basically, you are separating light."
Tae: "What do you mean, Toshi?"
Toshi: "White colored sunlight is composed of red, green, blue and the other colors."
Tae: "That's interesting!"

Satoshi: "I want to make a spectrum, too."
Tae: "OK! You can do next."
Satoshi: "All right! This is very pretty."
Mom: "Satoshi, do you know 'red'
Satoshi: "No, I don't."
Mom: "How about blue color?"
Satoshi: "I don't know blue either."
Mom: "Now, what color is this?"
Satoshi: "Rainbow color!"
Mom, Tae, and Toshi are all amazed at Satoshi, who didn't know any color but rainbow color.

Materials

A Flashlight	1
A clear plastic box-like container	1	(Alternatively, you may use a glass container such as a aquarium. *We had a very good result from a heat-resistant oven tray for pound cake.)
Water	(enough amount to fill your container)
A white drawing paper
Aluminum foil	(size:15cm X 15cm)
A small cutter knife

How to make a spectrum

1. Make a thin slit (1 mm width, 3 cm length) near the center of the aluminum foil using a cutter knife.
   Cover the front end of the flashlight with the foil. Position the slit at the center.
   
2. Pour plenty of water into the plastic container.

Arrange the flashlight, the plastic container, and a drawing paper, as shown in the drawing.

3. Switch off the lights to make the room dark.

Set the slit in the vertical direction. Direct the light to the plastic container to make a spectrum on the drawing paper.

• Slowly move the flashlight to find the best position for the spectrum.

• A spectrum can appear without attaching a piece of foil, but it looks blurred.

• There is another easy way to see a spectrum. Hold a mirror in water at a tilted angle (~30 degree) and the light is projected to the water surface.

   Thanks to light, we can see red sweaters, yellow bananas, and blue sky. Red, yellow, blue colors are not literally attached to these things. Instead, reflected lights give various colors. If lights were color paints, the spectrum would be a palette for various colors.

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