Water is clear and ice is clear, but you can usually see ice in your glass. Why is that? If you’ve ever tried to pick something up out of a pool of water, you know the object isn’t where your eyes tell you it should be. Why do diamonds sparkle more than glass and why does a prism give a rainbow? In this activity you’ll get to explore these questions and play with lasers at the same time!
Student Guide
Bendy Light
Experimenting with light waves from object to object
How does adding sucralose (sugar) to water change how the light moves through it?
This resource was originally published in PhysicsQuest 2015: Light Science.
How does adding sucralose (sugar) to water change how the light moves through it?
- Water gel cubes
- Sucralose packets
- Sugar packets
- Laser
- Binder clip
- Transparencies
- White paper
- Permanent marker
- Three cups
- Water
- Paper towels
- Ruler
Intro
Before the experiment
How do you think we are able to see clear objects such as glass or clear plastic?
Why can you see ice in a glass of water when they are both clear?
Take a cube out of the cup labeled “water” and put it in the cup labeled “sucralose water.” What do you see now?
Setting up
Fill three cups with water.
Label cup 1 “sugar” and dissolve the sugar into the water until no more sugar will fully dissolve.
Label cup 2 “sucralose” and dissolve the sucralose into the water until no more will fully dissolve.
Label cup 3 “water.”
Drop several gel cubes into each cup.
Allow the cubes to “grow” overnight in the cups. They grow in an interesting way so it's fun to pull them out every now and then while they are growing.
Unscrew the cap on the laser, shake out the batteries, and make sure to remove the tiny piece of paper between the batteries. Replace the batteries and push the button to make sure the laser turns on.
Put the laser in the binder clip so that the binder clip is pushing down the “on” button and keeping the laser turned on.
Take a cube out of a cup marked “water” and put it on a piece of paper towel and dry it off a bit.
After it's a bit drier, put it in the middle of the white piece of paper and trace around the base with the permanent marker. Label the paper “water.”
Aim the laser so that the laser beam hits the cube at a bit of an angle. It's easiest if the laser is far away from the cube.
During the experiment
Look in each of the three cups. What do you see? Turn off the room’s lights. Look at the gel cube. What do you see?
Stick your fingers in the cups. What do you feel?
You want to trace the beam of the laser both before and after it passes through the gel cube. The easiest way to do this is to put the permanent marker in the way of the beam and make a dot on the paper. Do this in three or four spots on each side of the gel cube. The laser beam is going to be kind of fuzzy after it passes through the cube so make sure you are putting the marker right in the middle of the beam when you are making marks.
Turn the lights on.
Use a ruler to connect the points and draw the laser beam both before and after it passed through the cube.
What can you say happens to light when it goes from the air to the cube?
What happens when it goes from the cube back to the air?
Put the transparency labeled “sugar water” on top of transparency labeled “sucralose water” and then put those two on top of the paper labeled “water.”
Line of the stack of transparencies and paper so that all “cubes” are on top of each other. The lines representing the incoming laser beams should also be lined up on top of each other. Draw what it looks like.
What do you notice about the lines coming out of the blocks? Are they lined up as well? If not, how are they different?
Conclusion
Does light always travel in straight lines? Cite evidence to explain.
What path would the laser beam follow if there was no cube at all? Draw that on the white piece of paper in a different color.
Which cube caused the light to bend the most?
“Index of Refraction” is a property of transparent materials that tells how much light bends when it passes through that material. The more light bends, the higher the index of refraction. Rank water, sugar water, and sucralose water from highest index of refraction to lowest index of refraction.