Mammoth Memory

Broken pencil

A pencil viewed through the edge of a rectangular glass block at an angle other than 90° will appear to be broken.

Looking through a glass block at a pencil the pencil appears broken.

Picture looking from side.


Why does the pencil look broken? From above we can work out what is happening. The light ray from the pencil passes from a fast to slow medium and turns towards the normal line (remember FAST SOFA).

Path the light ray takes from the pencil through the glass block to the observer.

Picture looking from above.

The light ray passing through the glass block passes from a slow medium to a fast medium and moves away from the normal line (again remember FAST SOFA).

If you look at an animal from the side of a tank that is half in the water and half out of the water, it can look split. This is refraction in action.

A duck can appear split in half at the surface of the water due to the effect of refraction.


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