Everyone loves the lights of the holiday season. White, green, blue, red and other colors shimmer in the cold evening air. Did you ever wonder about the colors of lights? What causes us to see different colors?
Human eyes are able to see a variety of colors, and each color has its own wavelength and frequency. Human eyes see green light best. Green light has a shorter wavelength and higher frequency than yellow, orange or red light. Blue and violet light have shorter wavelengths and higher frequencies than green light.
Light waves are transverse waves. This means the light wave travels at a 90-degree angle to the height of the wave. Water waves are another example of transverse waves. Sound waves are a completely different kind of wave. Sound waves are compression waves. The compression travels in the same direction as the sound wave.
Light waves also can travel in a vacuum where there is no air. This is why we can see the sun's light even though it travels to us through the vacuum of space.
Activity: Modeling a light wave
You will need the following:
1. A Slinky, or "lazy spring," is a walking spring toy. The Slinky was invented in the early 1940s, and the first Slinkys were sold in 1945. It was named the official state Toy of Pennsylvania in 2002. The metal Slinky (original or junior) works best for this activity.
2. A long area to stretch out the Slinky spring; you will need a space at least 3 meters (10 feet) long.
3. A friend, brother, sister or parent to help on the other end of the stretched out Slinky.
4. Stretch the Slinky spring out. You hold one end of the Slinky and have your friend hold the other end while you both are standing at least 2 meters (6.5 feet) apart.
5. Move your end of the Slinky repeatedly up and down slowly over a total of about 15 cm (6 inches). Notice the amount of energy you are putting into the putting into the Slinky. What else do you notice?
6. Now move your end of the Slinky a little more quickly (still up and down 15 cm). Are you putting less or greater energy than before into the Slinky. What do you notice? Is the Slinky wave different or the same as the slow wave?
7. This time move your end of the Slinky as fast as you can up and down over a range of 15 cm. Notice the relative amount of energy in the Slinky wave. What can you say about the wavelength of the three Slinky waves: "slow," "a little more quickly" and "as fast as you can"?
Note: Please be careful with your Slinky and hold on tightly to your end!
What happens to the wavelength of the Slinky wave when you add energy? Discuss this with your Slinky wave partner.
Frequency is the number of waves that pass a point in a single second. Wavelength is the distance from one point to the same point on another wave.
All light travels at the same speed. Only the wavelength and frequency change. The wavelength and frequency cause us to see the various beautiful colors of light during the holidays and every day.
- Libby and Robert Strong and Richard Pollack work with the SMART Center, a hands-on science outreach and education organization in the northern Ohio Valley, the headquarters of which is located at the SMART-Centre Market, 30 22nd St., Wheeling. Visit them at www.smartcenter.org.