Refraction of light
How to make a rainbow
Background
Refraction
(check out the definition in the online science dictionary) is something that causes strange effects with light. The most obvious one, of course, is the rainbow.
(Check out the project
Refraction – fact or fiction
for more strange effects.)
Imagine being alive way back before scientists discovered why rainbows were formed. People must have wondered how all these pretty colors ended up in the sky. And, hey, they always appeared after it rained? Huh?
Well, lucky for you, you live in this age and you know about science. This experiment is going to show you how rainbows are made – and we have great scientists like Sir Isaac Newton to thank for doing all the groundwork...
Let's do science...
The Experiment
I am going to explain two different experiments to you that have the same results and conclusion. The first one you should be able to do at home with the equipment you have around the house. The second one needs some special equipment, which if you can get hold of and do the experiment will impress the socks off anyone who sees it. But do not despair if you can't get that equipment. Basically, what needs to happen is you need to refract white light and then find a way to see the resulting colors. Both ways outlined below will allow you to do this.
The Aim
To create a rainbow with all its colors using refraction.
HINT: Need I say that these experiments are best done in darkened conditions! This means that you need to have someone ready with a camera to capture your rainbow that you make, as it will be difficult to repeat the experiment in your project display.
Experiment 1:
Equipment Needed
A torch
A glass, “see through” rectangular bowl, fairly shallow
A small mirror
A white piece of cardboard or thin tissue paper
Water
Method
Pour the water into the glass bowl, until it is about half or three quarters full.
Balance the mirror against the side of the bowl and in the water at an angle, with the mirror pointing up out of the water.
Shine the torch from above the water, through the water onto the mirror.
Hold the white cardboard above the mirror until you have the reflection from the mirror on it.
Alternatively, make a frame with the cardboard and stick the tissue over the cardboard, much like a screen. When you get the image onto the tissue screen you will be able to see it from the top as it will shine through, rather than have to look underneath to see the colors.
HINT: If you have a sunny window and you look at the reflection of it in the mirror in the water, you can also see the colors of the rainbow.
(The photo below gives you a visual picture of what I have said in the method above...)
Experiment 2:
Equipment needed
A
prism
(see the definition in the online science dictionary)A strong light sourceA piece of cardboard or plastic with a small slit in one sideA white piece of cardboard
Method
Set up the light source and the cardboard with the slit so that the light shines through the slit creating a thin beam of light on the surface you are working on.Place the white cardboard so that the beam of light shines onto it.Place the prism in-between the light source and the white cardboard so that the beam of light passes through it. Move the prism around while watching the white cardboard.Results
This is what you should see happening... Experiment 1: The cardboard has the colors of the rainbow shining on it. (Check out the photo below. This is what I got when I tried this experiment out at home.)
Experiment 2: While watching the cardboard and moving the prism, you will notice rainbow colors. By moving it you will be able to get the best position for the best rainbow.
The Conclusion
In both situations above, the white light was split into it's seven colors. This happened because of refraction of light in the water in experiment 1 and in the prism in experiment 2.
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