Have you ever wondered why we see red sunsets even though the sky is blue? Try this experiment to learn why!
- a flashlight
- A clear container with flat parallel sides
- 1 cup of milk
- Put your container on a table that allows you to see it from all sides. Then fill the container ¾ full of water.
- Then put the flashlight against the side of the container so that the light from the flashlight shines through the container. Write down your observations on how easy it is to see the light beam shining in the container. Also write down your observations about the colour of the beam from different positions of the container.
- Add ¼ a cup of milk to the water in the container and stir it. Now put the flashlight against the side of the container so that the light from the flashlight shines through the container. Write down your observations on how easy it is to see the light beam shining in the container again. Also, write down your observations about the colour of the beam from different positions of the container.
- Again, add another ¼ a cup of milk to the container and stir it and again write down your observations about the visibility of the light beam and its colour.
- Finally, add the rest of the milk to the mixture and write down your final observations.
- You will have noticed that the more milk you add, the more the light beam is easier to see. Also, the light from the flashlight looks blue from the side of the container but orange when you look at it head on.
- Why does this happen? Well usually light travels in straight lines except when it hits the edge of the container. When the beam from the flashlight travels through the water we cannot see the beam from the side because the water is uniform and so the light travels in a straight line. The same thing happens when light from the sun travels through the air.
- When you add milk to the water, the particles of fat and protein in the milk are suspended in the water. These milk particles scatter the light and make the beam of light visible from the side. The more milk you add the more the light scatters, causing differences in observations as you add more milk. The blue light is scattered more, while the orange light is scattered less. This means that the orange and red-light travels in more of a straight line.
- This experiment shows us how we see red sun sets because the light you see when you look at the sky is sunlight scattered by particles of dust in the atmosphere. The sunlight scattered by dust in the atmosphere is scattered in the same way the milk particles scatter the light from our flashlight. Looking at the sky when its blue is like looking at the scattered beam of light from the side. Meanwhile, looking at the beam of light head on when it looks orange or red is like looking at the sun set, we are looking at non-scattered light.
For more information and pictures please visit http://scifun.chem.wisc.edu/HOMEEXPTS/BlueSky.html