Light refraction in a glass of water makes a straw appear to be broken or bent

Experiment to demonstrate the principle of refraction

Ever reached down into the bath tub water to grab a toy and found that it was not in the position it appeared to be in? What you are experiencing is the effect called refraction. When light enters the water (or any transparent material) it slows down slightly. If the light enters the water at an angle then this change in speed causes the light beam to bend away from its original path. This is called refraction.

Let’s conduct an experiment that allows us to see the effect of refraction.

  1. Fill the glass 2/3 full of water.
  2. Place the pencil in the glass holding it straight up and down (i.e. not at an angle). Notice that the pencil still appears straight when viewed through the side of the glass.
  3. Now take the pencil and let it lean against the side of the glass. Look through the glass at the pencil. Notice that it appears bent. This is the effect of refraction or bending of light.

So if light is bent when passing through a transparent material, does this mean that everything we see through our clear glass window is actually distorted and not in the position that it appears to be? Yes and no. Refraction does occur but the effect of the bent light actually cancels itself out. Remember that a clear glass has 2 surfaces that the light passes through – the inside surface of the glass and the outside surface of the glass. When the light passes through the inside surface of the glass the path is bent in one direction and when the light passes back out through the outside surface of the glass it is bent in the other direction, hence canceling out the effect of refraction. Everything inside the glass window is pretty much located exactly where it appears to be.

Experiment Supplies

Supplies: Pencil, glass of water

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