Prism: Composition of Light

• To understand how a prism works and to learn about its properties
• To understand the concept of dispersion

Have you ever seen a rainbow? Why do you think rainbows may appear after it rains? Let us get a piece of glass and hold it up to the sun and try to make a ray of light separate into the seven colors of the rainbow, which is called a spectrum. In this lesson, we will answer the following questions.

How and why can a prism split white light into seven colors?

A prism separates white light into a group of seven colors called a spectrum. These seven colors are always in the same order. The colors of the spectrum are red, orange, yellow, green, blue, indigo, and violet. You can make up a name by using the first letter of each color to form a person's name. ROY G BIV Light can be reflected and bent. When light passes into the prism glass it slows down and it bends. The color red is not bent in the same way as the color violet is bent. When the colors come out of the prism, each color is bent in a different way and in a different quantity. People hang prisms from fancy lights in their homes or from windows that the sun shines through in their homes in order to fill their rooms with rainbows.

After it rains, there are lots and lots of water droplets in the air, around us. When the sun comes out, white light will strike all the drops of water. Each and every water drop of the millions and millions of water droplets acts just like a prism in that it separates the single strand of white light into seven colors. Sunlight enters each and every drop of water and the colors are given out as if the drop of water was a prism. This bending and reflecting happens at the same time in all the droplets of water and that is what forms the colors of the rainbow that you see after it rains.

You can make your own rainbow-one that works exactly like one you might see in the sky. On a bright, sunny day, take a garden hose and use your finger or a nozzle to spray a fine mist up into the air. You will see a rainbow form in the water droplets as they fall from the fine mist up in the air.

Rainbows have no end, because they are circles. You can see the complete circle of a rainbow from an airplane. There is a reason why you can't see the end of a rainbow from the ground. For you to see a rainbow, raindrops have to be falling somewhere in front of you, and the sun has to be somewhere behind you. That way the raindrops can reflect the light from the sun back to your eyes. You see that light as the colors of the rainbow because light from the sun is made up of all possible colors. Sunlight gets separated into those colors when it hits the raindrops.

If you try to walk to the end of the rainbow, the rainbow will keep moving with you. The droplets are still in front of you, and the sun is still behind you, so you can never get to the end!

• Inclined plane, with 3 different trackterminals — 5491.11
• Projector with 12V 20W halogen lamp — 4414.18
• Equilateral glass prism (side 25 mm) — 4450.10
• Prism table — 4418.29
• Holder for slides and diaphragms — 4414.03
• Set of seven diaphragms — 4414.12

• Name all of the colors, in order, which can be found in a rainbow.
• Why do raindrops, droplets of water, split white light into colors just like a prism?