Vanishing Glass

Refract light to make an object vanish in water

With some everyday household objects, you'll have your friends and family thinking you're a magician. You'll have the power to make glass vanish right before your, and their, very eyes. It might not be actual magic, but it is definitely an amazing science experiment about index of refraction that will make an object appear invisible.

Materials

3 clear glass beakers (or clear cups)
Wesson oil
Water
Pyrex stirring rods (must be pyrex glass for this experiment to work)

Experiment
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Begin with 2 of the glass beakers (or cups).
Fill one of the beakers half full with water and fill the other half full with Wesson oil.
Take one of the pyrex stirring rods and place it in the beaker that is half-full with water. You can see the stirring rod perfectly clearly, can't you?
Use another pyrex stirring rod and place it in the beaker that is half-full with Wesson oil. What happens to this stirring rod? It disappears!
Take your last beaker and fill it half-full with water.
Gently fill the beaker the rest of the way full with Wesson oil. If you did it right, you should have a beaker with water on the bottom and Wesson oil on the top.
Submerge another stirring rod into the beaker with the two liquids in it. What happens to this stirring rod? Why do you think this happens?

How does it work?

Translucent and transparent substances each bend light at a different angle, allowing it to pass through at different speeds. The refractive index measures the speed at which light moves through the substance. The more that light is bent (refracted) as it passes through a substance, the higher the refractive index of the substance.

If we compare water to Wesson oil, we find that Wesson oil has a higher refractive index number than that of water. When the first pyrex stirring rod is placed in the water, we see that light moves more quickly through water than through the pyrex stirring rod. But when the pyrex stirring rod is placed in the Wesson oil, we see that the two substances have very similar refractive index numbers.

When the pyrex stirring rod is placed in the Wesson oil, it disappears. Because the refractive index numbers of pyrex and Wesson oil are very similar, the light is not altered as it passes through the pyrex stirring rod. It appears that the light is only passing through the Wesson oil.

Additional Info

Try taking this experiment further by researching other substances and objects that share refractive index numbers. Our Vanishing Jelly Marbles is a great way to get started.