Sometimes when you look into a swimming pool it’s difficult to tell how deep the water actually is. If you grab something long, like a stick, you can use it to test the depth of the water. Upon putting it in the pool though you might notice something funky. The stick looks like it bends! This is due to light refraction. Light refraction is caused when the ray of light travels through different mediums and slows down or speeds up. In the case of this stick in the pool, water and air are two different mediums. When light travels through air it can move quickly, but as soon as it travels through water it slows way down. Molecules in the air are spread out, which is why little refraction occurs through air. However, the water molecules are closer together and this makes it more difficult for light to travel through the. Similarly, we have a much easier time moving through air than we do through water! When the light waves slow down, it will appear as though the stick has bent, but we know that it is still straight. Our eyes trick us into seeing the stick as bent. You might not have a pool at home to try this with, but you can try it on a much smaller scale!
Materials: Clear drinking glass, water, penny, plate.
Directions: Place a penny on a flat surface and put the glass on top of it. Take the plate and put it on top of the glass. You can still see the penny. Now remove the plate and fill the glass with water. Once you have filled the glass, put the plate back on top. Do you still see the penny now?
How it Works: Light can travel easily through the air which is why we could see the penny when the glass was empty. When we added water to the glass, the light waves slow down. These light waves are refracted and can’t make it to our eyes! The glass also refracts the light even more and the image ends up closer to the top of the glass. With the plate on top of the
glass, we cannot see the penny! Remove the plate and look straight down. Sure enough, the penny is still there.
Want more? Research it!: How does light refraction create rainbows? Email email@example.com with what you learn and you could be featured on our Facebook page!
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Carlie Wright is the education programs coordinator at ECHO, Leahy Center for Lake Champlain. The center, which works to engage families in the joy of scientific discovery, partnered with the Burlington Free Press to publish this feature.
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