What you need: 1 glass of water 1 pencil

How do you perform the experiment?

Put the pencil slantwise into the glass filled with water.
Observe it from all sides.

What do you see?  yes  no  Nothing happens.      The pencil is broken.      It looks as if the pencil is broken.      If you look at it from above, the pencil is bent downwards.        if you look at it from the side, the pencil seems bent.

Explain the "bending" of the pencil with the law of refraction.

We have seen that a light ray is bent at the water surface. Explain now why the pencil seems to be broken.
Note: You can only see the pencil as light rays, leaving it, reach your eyes. What happens to those rays which come from the part of the pencil under water?
If this explanation is too difficult, go back to the figure at the bottom of experiment number 5.


Both pictures show what you can see: if you look at it from a different angle, the image differs. On their way from the object to you eye, the light rays undergo many (and often complicated) refractions.

The light rays leaving the pencil are broken at the water surface. Our eye is unaware of this, so it sees the rays running straight forward. So we think the pencil lies in the extension of the stright line from our eyes.