Explorers Club

In February 2009 the Explorers spent a session investigating the nature of light. They learned that white light is actually anything but white, and that nearly every beam of light has a secret rainbow hiding inside it.

The Explorers started the session by performing a classic science demonstration first performed by Isaac Newton, using a prism to separate light into its component colors. A prism is simply a thick piece of triangular-shaped glass. Most people know that light travels at a constant speed of 186,000 miles per second, but many are not aware that this is only true for light traveling in a vacuum. When light enters a different medium such as water or glass, the speed of light slows down.

The energy of any particular source of light depends on its frequency or wavelength, and light of different frequencies travel at different speed when they enter a substance like glass. So, when white light enters a prism made of glass, each separate frequency of light travels at a different speed for the time that the light is in the prism. This leads to the frequencies separating and spreading out from one another once the light leaves the other side of the prism.

Since our eyes perceive different frequencies of light as being different colors, this means that passing white light through a prism will result in a rainbow of light emerging at the other end. One of Newton's most important discoveries was that he could not only turn white light into a rainbow, but that he could then turn the resulting rainbow back into white light by focusing it through a second prism.

The Explorers discovered that not only will a prism turn white light into colors, it will also distort images passing through it and make them appear to come from different directions than they really do. This is because the prism both bends light (called refraction), resulting in the separation into colors, and also bounces it in new directions (called reflection). This discovery of reflection proved to be a source of great amusement to the students, as they could see their friends' eyes peering out at them from unexpected places when the prism was in front of their eyes.

After admiring the prism and its rainbows and distorted images, the students moved on to the next activity. The goal here was to echo Newton's triumph of blending colors back into white, but instead of using a prism they used poster board, colored construction paper, and string to make the attempt.

The students began the project by cutting out a pair of paper plate sized circles from white poster board and gluing them back to back. Next, they traced and cut pie-shaped wedge shapes from six different colors of construction paper: red, orange, yellow, green, blue, and purple. On one side of the white wheels they glued one "full-sized" wedge of each color all the way around the wheel. On the other side, they split each full-sized color wedge into three smaller wedges and glued them around the wheel in the same pattern.

Next, the students each poked two holes (using first a push pin and then a sharp pencil to enlarge the holes) near the center of the wheel, just a bit less than an inch apart. A three-foot length of thick string was passed through each of these holes. Finally, the two strings were tied off to each other at both ends.

Now, the color wheels were ready to test. The students took turns in pairs, with one student holding the strings (looped over their hands at each end) wide while their partner twirled the wheel in the center until the strings were tightly wound around each other. (See the photo above to see how this worked, along with what one of our color wheels looked like when finished.) Then the partner let go while the student holding the strings pulled the ends tightly apart. This made the wheel spin rapidly as the pair of wound-up strings unwound themselves.

The theory here was that if the spinning was rapid enough, the colors on the wheel would blend together and become indistinguishable to the eye, merging back into white. Did it work? Well, sort of. We did indeed succeed in blending the colors until each individual color essentially disappeared from sight, but instead of a pure white color we ended up with shades ranging from pinkish to a pale brown. Why? Perhaps the spinning was not truly rapid enough, or perhaps the hues of our construction paper did not sufficiently match the colors in a true rainbow. Either way, we did manage to successfully demonstrate that the colors will blend and merge, so we considered that to be a success.

As for making the two sides of each color wheel differently, our hypothesis there was that the side with more color wedges would blend together more efficiently, because each section of color was smaller, thereby making a smoother transition as the wheel spun. This part of the experiment met with mixed results: some of the students reported that they indeed thought that the blending was better on that side of the wheel, while others said they saw little or no difference between the two sides.

Click on the word Gallery below to see some photos from our activity on this day.

Gallery