By: writer Rookie parenting Science

Refraction of Light

Have you ever before noticed if girlfriend look through a glass of water, the image behind the glass occasionally looks funny or distorted?

It’s choose the glass that water is play tricks on your eyes.

You are watching: Why does a straw look bent in a glass of water

The cheat is actually created by the refraction that light.

Light travels at different speed through various materials.

As a result, the light “turns” when it passes from one medium to another.

There space somany an excellent refraction of irradiate experiments we desire to do.

Let’s begin with these 2 simples ones.


Light Refraction Experiment


Experiment 1Put a straw right into the glass that water vertically and also watch indigenous the side.Slowly tilt the straw and also watch just how the straw shows up to be broken at the water surface. Experiment 2Raise the glass or reduced your eye to look at the straw from under the water surface. The straw shows up to it is in bent instead of broken.Move to different angles and watch exactly how the straw seemsto change in form at the water surface ar as girlfriend move.


Why:Experiment 1

Light bends as soon as it passes from one tool (air) into another medium of a various density(water). This bending that light, called refraction, causes the straw to look broken​1​. The section of the straw the is submerged in water also appears come be broader than the portion of the straw over the water.


Since the glass is reasonably thin, we deserve to assume not lot refraction takes place there. So the optical illusionsare mainly caused through the water inside.

However, even though the irradiate bends in ~ the water/air interface, our brain does not recognize that or account for that. Ours brains believe that light always travels in a directly line and also extend the light rays backward to a location different from the initial straw. The is why the submerged part of the straw appears to be shifted in water.

When ns was law this experiment with my 4 year old daughter, she retained saying that the straw need to be broken. Yet I maintained pulling it out of the water to present her that it wasn’t damaged at all. She was fascinated.


Why: Experiment 2

Light bends once it passes from water into the air. As soon as the light comes from a location close enough to the surface (or the angle that incidence is larger than water’s critical angle) the light bends so lot that instead of passing out into the air, all of it reflects ago into the water as if the water surface were a mirror. This is calledtotal interior reflection.

Diagram below: once there is full internal reflection, your brain thinks the the underwater fish is at over the water (and upside down).


This is what happened when friend looked at the straw from listed below the water surface. The reflected straw appears to it is in connecting in between the above-water part and the under-water distortion. That is why the straw looked crooked.


What did girlfriend see once you relocated your head to various positions? deserve to you think that some fun experiments to do using this refraction property of light?


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