To investigate the wavelength properties of visible light.
- copy of "What's Your Wavelength?" student handout
- transparent plastic or glass container (about 30 cm (12 in) long, 20 cm (8 in) wide, and 15 cm (6 in) high)
- powdered milk
- spoon or stirring rod
- blank white card for image screen
Once students understand that there are a number of ways to detect radiant
energy invisible to our eyes, have them investigate the wavelength properties
of the radiant energy they can see: visible light. Explain that as light from
the sun passes through earth's atmosphere, it collides with air molecules,
producing a scattering effect. Students can use this activity to investigate the effects of the earth's
atmosphere on different wavelengths of light.
Organize students into groups and give each group a copy of the "What's Your Wavelength?" student handout and a set of materials.
The activity works best in a
darkened room. Once students have done the activity, facilitate a discussion
about what causes the colors students see and why the colors change. (see Activity Answer for more information.)
What's Your Wavelength?
This experiment helps to explain why the sky appears blue and the sun
looks yellowish orange. As the sun's light shines on the earth, shorter
wavelengths are scattered by the atmosphere. Blue light scatters more than the
other colors, making the sky blue and leaving the remaining transmitted light a
predominantly yellowish orange hue (the color of white light minus blue).
This scattering effect can also be noticed in the apparent color change of the
sun as it rises and sets. When the sun is at the horizon, light must travel a
longer distance through the atmosphere to your eyes than when it is overhead.
During this time, most of the blue light is scattered out, leaving a reddish
orange color. When the sun is directly overhead, the least amount of scattering
occurs, so the sun looks white.
Students might notice that violet light has an even shorter wavelength than
blue light, prompting them to wonder why the sky appears blue rather than
violet. Even though violet light scatters more than blue light, the sun puts
out a greater quantity of blue light compared to violet light. You might want
to tell students that in 1910, at the age of 31, Einstein came up with a
mathematical formula describing why the sky is blue.