Have you ever looked at a straw in a glass, and it seems like it is in two separate pieces? Have you ever reached down to grab something underwater, and had to move your hand sideways to actually grab it? Both of those situations are examples of how water bends or refracts light. In this activity we will explore how refraction through water creates rainbows.
Refraction, or the way light bends when it travels through different materials, was explained for the first time by a mathematician from Iraq named Ibn Sahl. He wrote a mathematical formula for how light bends through glass in the year 984 CE. He showed that you can predict how much light will bend when it passes through something that is not air. Since then, many more people have used this idea to calculate the speed of light through various materials. Isaac Newton did many experiments with prisms to try and learn how light and color were related, and further advanced scientific understanding of refraction.
Fill the jar about three-quarters of the way with water.
You should see a rainbow appear on the white paper. This is happening because different colors of light refract or bend at different angles through the water. White light, like from the sun or a flashlight bulb, is made up of a mix of all of the colors, which can be separated out using something like a prism, or a glass of water. The red light bends the least as it passes through the water, and violet light bends the most. That is why rainbows are always in order from red to violet.
Make sure to clean up when you are done. Pour the water down the drain, recycle the paper, and put the jar and flashlight back where they belong.
What if the light you are shining on the jar is not white light? Does that make a difference? Does an LED flashlight give different results than a flashlight with an incandescent bulb? How does what you learned with this experiment apply to other rainbows you may have seen?
This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.
Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.
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