02.25.2016
Written By: Whitney Wenger
Why is the sky blue?
In continuation of last time’s experiments with light, we learned more about how light behaves in different media. The questions guiding this experiment included: why is the sky blue? When you put goggles on, why can you see farther in a swimming pool than in a lake or an ocean? Why is the city skyline hard to see some days and perfectly clear on other days? To understand how these things happened, we looked at how light scatters in different solutions.
The students first got a basis of how light behaves in different liquids by examining water, corn syrup, and oil with a flashlight and a laser pointer. While the laser pointer beam might look invisible as it passed through the water, you could see it glimmer in the bubbles in the corn syrup. The students then slowly poured a solution of watered down milk into a glass and shone a flashlight through the bottom of the glass, seeing what happened as they added more solution for the light to travel through. The flashlight originally looked white, but turned yellow and orange as they added more solution. We talked about how light was scattered by the proteins and other things in milk (milk is a colloid, after all!), and how certain light was reflected more than others, based on the light’s wavelength.
After these first two demos, the students then made their own solutions to test how light scatters. They explored what happened when you mixed different liquids (oil and water, for instance), and saw what happened over time as you add baking soda or sugar or even food coloring to their solutions. One student even recreated the pool and lake environments, which helped everyone see that the light did not scatter much in the pool analogy (water with food coloring), but quickly scattered in the lake analogy (food coloring with a mix of different liquids and solids added).