Things look displaced

The idea

An object partly immersed in water, or print under a glass slab, appears displaced or raised because light from it reaches the eye from a different direction after refraction.

A pencil in a tumbler

A pencil stands in a glass tumbler that is half full of water. Looking from the side, the pencil seems to be broken at the water surface.

Why does the pencil seem to be displaced at the water surface?

• The light from the part in water reaches the eye from a different direction
• The water makes that part of the pencil grow
• The water cuts the pencil in two

Why things look moved

In each picture the red lines are the real path of the light. The dashed grey lines show where the light seems to come from. Open every tab.

Seen from a new direction

Your eye assumes light travels straight. But the light bent on the way, so the eye places the object where the straight lines meet. That place is not the real one.

An object partly in water, or print under a glass slab, looks displaced or raised because light from it reaches the eye from a different direction after refraction.

Notes

Print under glass looks raised and an object partly in water looks displaced, because light from it comes to the eye from a different direction after refraction.

Check yourself

Why does the bottom of a pond look raised?

A pencil is partly in water. Which part sends light that seems to come from a different direction?

Letters are viewed through a thick glass slab placed over them. They appear

A pencil in water looks displaced by a certain amount. Would it be displaced by the same amount in kerosene?

• Light from the bottom bends at the water surface and reaches the eye from a different direction — correct. Yes!
• The water pushes the bottom upwards. The bottom does not move. It only looks raised because refraction changes the direction of the light.
• The water surface reflects the light back down. Reflection is not the reason. The light leaves the water and is refracted, which changes its direction.
• The part above the water. Light from the part in air goes straight to the eye. It is the light from the part in water that is refracted.
• The part inside the water — correct. Yes!
• Both parts equally. Only light from the part in water passes from water into air and is refracted.
• lowered. The light seems to come from a higher place, so the letters look raised, not lowered.
• at the same height as before. Refraction in the slab changes the direction of the light, and the letters look raised.
• raised — correct. Yes!
• No, the extent of the effect is different for different media — correct. Yes!
• Yes, it is the same for every liquid. The extent of the effect is different for different pairs of media.
• Yes, because only the pencil decides the displacement. The pair of media decides it. Kerosene and water would give different displacements.