Try This: Colors of Light

Color is a pretty interesting topic to study. In school, you probably learned to mix colors to make new colors. For example, green is made by mixing blue and yellow, and purple is made by mixing blue and red. In fact, every color can be made from the right combination of the three primary colors: red, yellow, and blue. But has anyone ever tried to convince you that red, blue, and yellow aren't the only primary colors? They aren't.

filter: a way to block certain colors of light from reaching your eyes.

QUESTION

What are the primary colors of light?

MATERIALS

Cellophane or plastic squares large enough to cover the light end of the flashlight. You will need 1 each of red, blue, and green.

3 flashlights

Rubber bands

A white screen or wall

Science Online

The EncycloZine has a collection of fascinating optical illusions. Visit www.encyclozine.com. From the main page, click on “Optical Illusions.”

Where does a mad scientist go to college?

A looney-versity!

PROCEDURE

  • Secure one square of cellophane or plastic to the end of each flashlight with a rubber band.

  • Turn on each flashlight to make sure it produces the correct color of light.

  • Carefully shine the red and blue lights onto the screen so that the color circles overlap. What color is produced?

  • Shine the red and green lights onto the screen. What color is produced by this pair of colors?

  • Shine the blue and green lights onto the screen. What color is produced by this pair of colors?

  • Carefully shine all three lights onto the screen so that all three colors overlap in the middle. What color is produced by all three colors?

WHAT'S HAPPENING

Light behaves differently than paint does. Red, blue, and green can combine to form every color of light, so they are called primary. Secondary colors are formed when two primary colors are mixed. These were the first three colors you produced: magenta, yellow, and cyan (blue). When you shined all three colors onto the screen, you should have produced white light. If your cellophane covers weren't totally pure (most aren't), you may have seen an off-white color.

FOLLOW-UP

Try looking at the world through the red, blue, or green filters. You will probably notice that most of what you see is the color of the filter you are looking through. But you may also see some objects that look black. The light from these objects is being blocked by your filter, so you see no color.

Black and White

Can you find the figure that is the EXACT opposite of the three figures in the box below? Draw a line between each pair.

KIDS' LAB LESSONS

QUESTION Which color is hotter: black or white?

EXPERIMENT OVERVIEW In this experiment you'll be testing to see whether a black object heats up faster than a white object. You'll test the temperature of water inside a can of each color and also test the temperature of the air under a card of each color.

SCIENCE CONCEPT Each color of light that we see reaches our eyes because it has reflected off another object. All the other colors of light that hit that object were absorbed. Some objects absorb more light than others. In fact, white objects must reflect all the light they receive, which means they don't absorb any. On the other hand, black objects reflect no light to our eyes, which means they absorb all the light they receive. This experiment will show which of these two ends up being warmer.

MATERIALS

2 thermometers 2

sheets of paper: 1 white and 1 black

2 tin cans: 1 painted white and 1 painted black (have an adult help you paint the cans)

Pitcher of water

PROCEDURE

  • Place the thermometers outside and lay one sheet of paper over each one.

  • Let them sit for 30 minutes.

  • Remove the papers and compare the temperature each thermometer shows.

  • Fill each can with water at the same temperature and place the corresponding sheet of paper on top to cover it (black on black, white on white).

  • Set both cans outside for 30 minutes. Remove the papers and compare the temperature of each can of water.

QUESTIONS FOR THE SCIENTIST

  • Which thermometer measured a higher temperature in the first experiment?

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  • Which can of water was warmest?_________________________________

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  • On a cold day, which color would be better to wear to school — black or white?

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  • If you lived in a very hot place, what color car would you buy if you wanted to stay as cool as possible?____________________________________________

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