Author: Maddie Van Beek
Think back to a time that you’ve stood in a pool or a lake. When you look down, do your legs look like they normally do? No! Have you ever wondered why your legs look bent, or as if they are shorter? This weird effect is called refraction!
Refraction happens when a wave travels from one medium to a second medium in which the wave travels at a different speed (the speed of light is only constant in a vacuum). For example, when light goes from traveling through the medium of air to the medium of water, the speed of the light slows down and the wavelength shortens (the frequency of the wave—that is, the number of times the wave repeats in a given time—remains the same). The amount of refracting that occurs depends on the index of refraction. We can calculate the index of refraction (n) by dividing the speed of light in a vacuum (c) by the speed of light in that specific medium (v). That is:
Index of refraction = vacuum/specific medium
n = c / v
For example, the speed of light is 299,792,458 meters per second, but is commonly denoted as c. Let’s try calculating the refractive index for a vacuum.
Index of Refraction (n) = c (the speed of light) / c (the speed of light)
Anything divided by itself equals 1. Therefore, the refractive index for a vacuum is 1.
Below, you can see that the all other mediums have a larger refractive index than in a vacuum. This is because the speed of light in any other medium will be slower than in a vacuum. Therefore, the index of refraction will usually be over 1. Negative refractive indexes are only achieved with synthetic materials that possess uncommon refractive properties.
Think back to a time that you’ve stood in a pool or a lake. When you look down, do your legs look like they normally do? No! Have you ever wondered why your legs look bent, or as if they are shorter? This weird effect is called refraction!
Refraction happens when a wave travels from one medium to a second medium in which the wave travels at a different speed (the speed of light is only constant in a vacuum). For example, when light goes from traveling through the medium of air to the medium of water, the speed of the light slows down and the wavelength shortens (the frequency of the wave—that is, the number of times the wave repeats in a given time—remains the same). The amount of refracting that occurs depends on the index of refraction. We can calculate the index of refraction (n) by dividing the speed of light in a vacuum (c) by the speed of light in that specific medium (v). That is:
Index of refraction = vacuum/specific medium
n = c / v
For example, the speed of light is 299,792,458 meters per second, but is commonly denoted as c. Let’s try calculating the refractive index for a vacuum.
Index of Refraction (n) = c (the speed of light) / c (the speed of light)
Anything divided by itself equals 1. Therefore, the refractive index for a vacuum is 1.
Below, you can see that the all other mediums have a larger refractive index than in a vacuum. This is because the speed of light in any other medium will be slower than in a vacuum. Therefore, the index of refraction will usually be over 1. Negative refractive indexes are only achieved with synthetic materials that possess uncommon refractive properties.
When light passes from one medium to another, it refracts. What exactly does this mean? Let’s look at some examples!
| Refraction of light by water: Did this straw happen to break in water? Nope! It only appears to be broken. The light is refracted because it is going from air to water, causing the straw to appear distorted. |  Image 1 |
Try this yourself!
YOU WILL NEED:
YOU WILL DO:
Refraction also makes items appear to be in a different spot than they actually are. For example, think about trying to grab a diving stick in a pool. It may look like the stick is close, but it is actually deeper than it appears! you ever dived for something in the pool? Under water, an object's actual depth is often different from that of its apparent depth. Test it out!
YOU WILL NEED:
YOU WILL DO:
In the image below, you can see that the design on the wall behind the water is flipped inside the glass! How does this happen? Refraction! Watch the video below to learn more about refraction in the next activity, "The Magic Arrow!"
YOU WILL NEED:
- A pencil
- Water
- A clear cup
YOU WILL DO:
- Place a pencil in an empty clear cup. Draw what you see.
- Hypothesize how adding water to the cup might change your view of the pencil.
- Fill the cup half full of water.
- Record what you see! Look at how your view of the pencil changes at the surface of the water. Does it look different than it normally does?
Refraction also makes items appear to be in a different spot than they actually are. For example, think about trying to grab a diving stick in a pool. It may look like the stick is close, but it is actually deeper than it appears! you ever dived for something in the pool? Under water, an object's actual depth is often different from that of its apparent depth. Test it out!
YOU WILL NEED:
- A bowl
- A penny
- Water
YOU WILL DO:
- Place the penny in the bowl.
- Back away. Eventually, you will not be able to see the penny.
- Keep the penny in the bowl and fill the bowl with water.
- Make a hypothesis--will adding water make any difference? What might water change?
- Once again, back away. Can you see the penny?!
- Why is it that you can see the penny the second time and not the first time?
In the image below, you can see that the design on the wall behind the water is flipped inside the glass! How does this happen? Refraction! Watch the video below to learn more about refraction in the next activity, "The Magic Arrow!"
Image 2
Try it out for yourself!
YOU WILL NEED:
YOU WILL DO:
YOU WILL NEED:
- A clear cup
- A marker
- An index card
- Water
YOU WILL DO:
- Draw two arrows on your index card. They should both be pointing in either the right or left direction.
- Hold the index card behind an empty glass cup. What do you see? Record your thoughts.
- Keep the index card behind the cup, and fill the cup until it reaches the level of second arrow. What happens to the bottom arrow?! Why does this happen?
What other kinds of refraction are there?
Mirages: Now, I’m not talking about hallucinations. I know some of you may think a mirage is like the vision of a beautiful oasis that a thirsty traveler imagines in the desert.
The truth is, I bet all of you have seen a mirage. Have you ever driven on a hot day and seen what appeared to be puddles of water on the hot tar ahead of you, only to have them disappear as you draw nearer? That’s a mirage! What causes this odd phenomenon?
We know light bends when it passes through different mediums. Did you know that even cold air and hot air can be considered different mediums? When light travels through different air temperatures, the light bends. Cold air is denser than warm air, so it has a greater refractive index. As light passes from the warm air to the cold air, it is bent upwards, so you end up seeing a refracted image of the sky on the tar.
Mirages: Now, I’m not talking about hallucinations. I know some of you may think a mirage is like the vision of a beautiful oasis that a thirsty traveler imagines in the desert.
The truth is, I bet all of you have seen a mirage. Have you ever driven on a hot day and seen what appeared to be puddles of water on the hot tar ahead of you, only to have them disappear as you draw nearer? That’s a mirage! What causes this odd phenomenon?
We know light bends when it passes through different mediums. Did you know that even cold air and hot air can be considered different mediums? When light travels through different air temperatures, the light bends. Cold air is denser than warm air, so it has a greater refractive index. As light passes from the warm air to the cold air, it is bent upwards, so you end up seeing a refracted image of the sky on the tar.
Image 3: Mirage in the Mojave Desert
Rainbows: As you know, as light passes through different mediums, it refracts, or bends. Droplets of rainwater can cause light to bend, thus creating a rainbow.
Image 4: Rainbow in Grodnow, Belarus.
References:
- http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c3
- http://en.wikipedia.org/wiki/Refraction
- http://teachinginroom6.blogspot.com/2012/04/light-refraction-fun-independent.html
- http://science.howstuffworks.com/nature/climate-weather/storms/rainbow1.htm
Image and Video Credits in order of appearance:
Image 1: Bcrowell, 2014. Refraction-with-soda-straw-cropped. Uploaded from Wikimedia Commons on 7/31/2016. https://en.wikipedia.org/wiki/Refraction#/media/File:Refraction-with-soda-straw-cropped.jpg File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license.
Image 2: JrPol, 2015. Refraction in a glass of water. Uploaded from Wikimedia Commons on 7/31/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/R-DSC00449-WMC.jpg/800px-R-DSC00449-WMC.jpg File used in accordance with the Creative Commons Attribution-Share Alike 4.0 International license. No changes were made.
Home Science, 2014. Amazing water trick - Amazing science tricks using liquid. Uploaded from Youtube on 7/31/2016. https://youtu.be/G303o8pJzls
Image 3: Inaglory, 2007. An inferior mirage on the Mojave desert in spring. Uploaded from Wikimedia Commons on 7/31/2016. https://upload.wikimedia.org/wikipedia/commons/7/7c/Desertmirage.jpg File released into the Public Domain.
Image 4: Сергей Banifacyj Морозов, 2008. Rainbow after the rain, Grodnow, Belarus. File uploaded from Wikimedia Commons on 7/31/2016.
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/%D0%A0%D0%B0%D0%B4%D1%83%D0%B3%D0%B0_%D0%BD%D0%B0%D0%B4_%D0%93%D1%80%D0%BE%D0%B4%D0%BD%D0%BE.jpg/1280px-%D0%A0%D0%B0%D0%B4%D1%83%D0%B3%D0%B0_%D0%BD%D0%B0%D0%B4_%D0%93%D1%80%D0%BE%D0%B4%D0%BD%D0%BE.jpg File used in accordance with the Creative Commons Attribution-Share Alike 4.0 International license. No changes were made.
