Program 31: Light & Color

I’ve always loved rainbows. There’s nothing more special than seeing a brilliant rainbow in the sky after a summer storm, or seeing dozens of miniature rainbows floating about your room thanks to a strategically placed prism in the window. But how do we see certain colors in the world around us? And is there a difference between the colors we see in, say, ink on paper, and the colors of light we might see in the sky via a rainbow?

I turned to “the master,” Bill Nye, to start off our Light and Color program to teach some key facts to our G3 scientists. Why does Bill Nye remain such a popular scientist with both kids and adults? He’s truly the master of honing a science topic down to a handful of key facts and concepts and presenting that information in such a fun and silly way.  We have a full line of Bill Nye DVDs at the library for anyone to check and take home, including his episode on Light and Color 🙂

From Bill, we learned (or were reminded of) several key facts about light and color:

  1. When we see a color in the world, we are observing the color that a specific object is reflecting. For example, we see a red apple as red because the apple is absorbing every single color except red. Red light is reflected, and thus that is the color we see for the apple.  For another example, if you are wearing a green t-shirt, you and everyone around you see it as a green shirt because it absorbs every color except green; green is reflected, and thus that is the color we see.
  2. White is all colors reflected; black is all colors absorbed.
  3. Black absorbs all colors and converts that light to energy or heat. This is why wearing a black shirt on a sunny day makes you much hotter than if you wear a white shirt. Or why sitting in black car in the sun is much hotter than sitting in a white car.
  4. colorwheelColored light behaves differently than colored pigments and dyes.  Most of us have heard the phrase “yellow and blue make green” before, right? And that’s true, at least for dyes/pigments. If you had yellow and blue paint, they would indeed mix together to make green paint. But what about yellow and blue light? For light, the primary colors are red, blue, and green. So, no colors combine to create green. But green and red light will combine to make yellow light. Or red and blue light will combine to make magenta light. Check out the color wheel to the right to see what some possible colored light combinations are.

OUR EXPERIMENTS

Experiment #1:  Chromatography

Chromatography is a term used to describe the separation of mixtures, usually with the help of a fluid.  As we know, black is the combination of all colors. So does that mean that black markers are the combination of all color dyes? Just a couple of colors?

Materials

  • Round filter paper or coffee filters  (we used 11 cm. filter papers; some experiments even use something as simple as paper towels)
  • A variety of black markers, including water soluble (washable) ones
  • Small plastic cups
  • Pipe cleaners, cut to size (for us, about 4-5 inches in length)
  • Some water (we used distilled, though tap water would work fine)
  • Table cloths (I mention them specifically because as you use water to separate the dyes in markers, you get the equivalent of water with food dye which can stain clothing, carpets, etc.)

A chromatography experiment can be done simply without some of these steps, but we’re scientists after all! We used Steve Spangler’s spin art experiment as the inspiration for our chromatography experiment. First we poked a hole in the center of the filter paper with our pipe cleaner, and then set the pipe cleaner aside. I instructed our scientists to put large, filled-in dots of black ink around the filter paper. You will see the best results if you put 4 or 5 large dots around the filter paper versus lots of tiny pin-point dots.  Next we dipped our pipe cleaners in the cups of water, making sure we pinched any excess water from the pipe cleaners. The final step was to put the pipe cleaner back through the center hole in the filter paper, and put one end of the pipe cleaner back into the water (like a flower stem going into water). The filter paper can simply rest on the top lip of the cup. You should notice water slowing moving from the center of the filter paper outward. Water is actually moving up the pipe cleaner stem thanks to friction, and is then flowing through the fibers of the filter paper in the same manner.

This process was actually a bit too slow for some of our scientists, so in most cases we pulled the filter papers off of the pipe cleaners, placed them on the table, and used the pipe cleaners to slowly drip water on the filter paper directly. Most of us only saw a partial separation of colors in the black dyes – namely, blue, some purple, and even some hints of yellow/orange. I also gave all of the scientists the opportunity to experiment with water soluble markers of other colors. We may not have had complete success in separating the black dye from the markers, but our scientists got to take home some pretty cool art!

Experiment #2:  Kaleidoscopes

Technically, this was more of a project than an experiment. I finally discovered a super simple way for our scientists to create kaleidoscopes of their very own…thanks to really nifty objects called rainbow peepholes.

Rainbow Peepholes

Rainbow Peepholes

Materials

  • Rainbow peepholes (you can buy these from various locations – I got mine from Amazon.com)
  • Recycled paper towel tubes
  • Duct tape or electrical tape (we used duct tape since I can get it cheap at the dollar store)
  • Scissors
  • Craft paper punches (optional – I bought a few at Michael’s in the scrap-booking aisle)

Steve Spangler was again our inspiration for this project. And the project is simple enough thanks to the peepholes, which are designed to naturally refract light. In fact, you can hold a peephole alone up to the light and you’ll see refracted light (in rainbows) through the peephole without the aid of a constructed kaleidoscope. To construct the kaleidoscope, you hold the rainbow peephole in place over the hole of one end of the paper towel tube, and then secure it in place with some tape….and you’re essentially done! You can cover the rest of the cardboard tube with tape to make it cosmetically more appealing if you’d like. Also, if you punch shapes out of circles of paper, hold them at the opposite end of the kaleidoscope, and then look through the peephole, you’ll actually see swirls of refracted color in the shape you punched. For example, I purchased punches for a star, puppy paw print, butterfly, and flower. If you punch a star out of a circle of paper, you’ll see star shapes in the kaleidoscope. According to the Steve Spangler site, you can also line the cardboard tube with tin foil for a dramatic result. We didn’t get a chance to do that, but you can give that a try at home and tell me what happens!

Experiment #3:  Colored Light

Materials

  • Flashlights (I got as many as I could at the dollar store so our scientists could work in small groups)
  • Sheets of colored cellophane (I got 8 1/2 x 11 sheets from Amazon.com)
  • Rubber bands
Red and blue light create magenta light.

Red and blue light create magenta light.

Red and green light create yellow light.

Red and green light create yellow light.

This experiment was inspired by something I read on HowStuffWorks about making colors. We didn’t have a ton of time to do this experiment (I was a little ambitious with my time), but our scientists got to at least try it out so that they can then attempt this one at home. Refer back to the color wheel for light at the top of this post. Our three base/main colors were red, blue, and green.  Grab 1 flashlight and place 2-3 layers of red cellophane over the top, held in place with a rubber band. Do the same with 2 more flashlights, but using green and blue cellophane. In some cases, I needed to play around with the lights to figure out how many layers of cellophane worked best. [I created multiple layers simply by folding the cellophane sheets.]

This experiment works best in a dark room (we closed the shades and shut off the lights in our program room). To create yellow light, take the flashlights with red and green cellophane. We found it worked best when we walked very closely to the wall so the light from each “colored” flashlight was very concentrated. Then you slowly move the two concentrated pools of light closer together on the wall. As they start to cross, you will see the new color of light emerge!

Below is an Animoto video highlighting some of the work of our G3 scientists with this program. See you next time for some fun with polymers!

 

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