Rainbows

by

Lois Polakoff

This lesson was created as a part of the SMART website and is hosted by the Illinois Institute of Technology

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.

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

2.  Name the seven colors of the rainbow.

3.  Explain how the rainbow in the picture above was formed.

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 as bent 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.

A scientist who did split light by putting a glass prism in a narrow beam of sunlight, actually saw a light that was broken into seven colors by a prism and his name is Isaac Newton.   These are important facts to know in regards to prisms.  Prisms can separate white light into a group of colors called the spectrum.  The spectrum is made of red, orange, yellow, green, blue, indigo, and violet.  Rainbows are very special displays of all the seven colors of light in the spectrum.  Since each raindrop bends and reflects sunlight just like a prism does, sometimes you can see a rainbow just after a rain shower just like the picture at the beginning of this project.

Answer these questions in complete sentences to see if you have learned about rainbows.

1.  Draw a diagram to show what a prism does to white light.

2.  Name all of the colors, in order, which can be found in a rainbow.

3.  Why do raindrops, droplets of water, split white light into colors just like a prism?

4.   What do you think would happen if you placed a prism in front of a spectrum of colors?

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!

Here is a great activity that you can try at home to see what white light is made of.

Get a flashlight, a mirror, a very large bowl of water, and some crayons.

Put the mirror in the very large bowl of water and shine the flashlight at the mirror.  Move the flashlight from side to side and up and down until you can see the reflection of colors on the ceiling or the walls.  Draw a picture of what you have seen on the ceiling or the walls.  Ask yourself these questions about what happened to the white light from the flashlight and what colors make up white light.  You can see all this from this activity if you do this activity correctly.