Refraction of Light Science Experiments

Here are some super cool refraction of light science experiments!

These experiments are so easy to do with materials that you have around your home or classroom.

I would recommend these experiments for kids in the upper elementary grades through middle school and even high school. Kids will be impressed and can understand that bending light is causing these cool effects. Teens can develop of much more full understanding of how refraction works, the refraction index of different materials (see the sugar water experiment below!) and the implications for everyday life.

Refraction of light refers to the fact that light rays slow down or speed up when they travel through different materials. For example, light travels more slowly through water than it does through air. This causes the light rays to bend, and it creates some cool effects and optical illusions.

Experiment #1: Magically Appearing Penny

Supplies Needed:

• A mug or cup
• A penny
• Water
• Something to pour from, like a pitcher
• Two people! You’ll need a partner for this one.

Start by placing a penny in the bottom of your mug.

Stand back from the mug, and move your head back until the penny just disappears from sight.

Have your lab partner slowly pour water into the mug.

They will need to pour very slowly and carefully so that the stream of water doesn’t dislodge the penny. If you pour too quickly, the penny will slide around in the bottom of the mug and then you’ll have to start over.

Keep your head in the same position. As the mug fills up, the penny should appear in your line of sight!

The Science Explanation:

Light hits the penny inside the mug and is reflected back to your eye. As the reflected light leaves the water in the mug and travels through the air toward your eye, it speeds up, causing the light rays to bend. Because of this, the penny under water appears closer to the surface of the water than it actually is.

Questions to Consider:

Did you have to have a certain amount of water in the mug before the penny “appeared?”

Did you see more of the penny when the mug was half full or when it was completely full?

Try this experiment with a wide mug and a narrow mug. Does the shape of the mug matter?

If you reach into a pond to grab a rock, will it be in the exact location that it appears to be?

Experiment #2: Broken Pencil

Supplies Needed:

• Glass of water
• Pencil

Here’s another classic refraction of light science experiment!

Place a pencil in a cup of water. Does it appear broken? It’s pretty weird! Again, this is the result of light traveling more slowly through water than through air.

The part of the pencil that is in the water also appears larger than the part sticking up out of the water.

Experiment #3: Backwards Letters!

Supplies Needed:

• Glass of water
• Index cards
• Markers

Here’s another fun trick to try with the refraction of light.

Fill a glass with water.

Then write your name BACKWARDS on an index card.

We enjoyed making Janie’s name go from backwards to correct with this experiment, but if your student can’t write their name backwards, then just have them write it the right way. They can flip it backwards with the experiment!

Place your index card behind the glass of water. The letters reverse directions!

Another fun idea is to reverse the colors in a rainbow.

The Science Explanation:

In this experiment, we have two factors going on – the water and the shape of the glass. The round glass creates a cylinder of water which acts as a convex or converging lens. Light rays from the right side of the card are refracted by the lens and end up on the left side as they enter your eye, and vice versa.

Here’s a great video on YouTube that explains how this works with some great illustrations.

Experiment #4: Refraction Index of SUGAR WATER

The refraction index of water is 1.33, but the refraction index of a saturated sugar solution is 1.49. This means that sugar water refracts light rays to a greater degree than water does. We decided to find out if we could observe the difference!

To make your sugar solution, heat the water until it’s hot but not fully boiling. (You can boil it if you want, but we didn’t.) Hot water dissolves a solute more quickly. Then stir in sugar 1 spoonful at a time until the sugar stops dissolving and just sinks to the bottom of the glass. We added more than 10 heaping spoonfuls of sugar to our water. You’ll be surprised at how much it can hold!

Side Note: I did a science fair project on this concept in 11th grade while taking physics. I created a rectangular box out of acrylic sheets and glue and measured the refraction of a flashlight beam with sugar and salt solutions of different concentrations. I won a ribbon at the regional science fair!

This experiment works best for middle schoolers and high schoolers because the differences aren’t dramatic. However, we could easily observe that the part of the pencil in the water appeared larger in the sugar solution than in the water. Also, the “break” in the pencil was visibly larger.

We also tried the mug and penny experiment with sugar water. The penny was visible sooner, with less water added to the mug. So cool!

Experiment #5: Dancing Rainbow

Use refraction of light to split white light into all the colors of the rainbow! This is an impressive and fun experiment, and you just need a mirror, water, and some sunlight coming through a window.

See the instructions here: Dancing Rainbow Science Experiment