Year 4 Science

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Put an apple in a bowl of water. What do you see? From the side, like in this picture, the part of the apple that's underwater looks a lot larger than the part above the surface, doesn't it? Why? What do you see when looking from the top?

Whenever you see something, you are seeing light rays bouncing off it. The light travels from the apple, through the water and the glass, then through the air before it reaches your eyes. Transparent materials allow light to pass through. But light moves less quickly through transparent materials than through air. So, water and glass slow light down much more than air, which you can see particularly well when your apple is half-in and half-out of the water.

The light rays change course just a little when they move from water to glass, then from glass to air. It is called refraction. Light leaving the water is bent closer to the surface. Those slight changes in the course of the light rays travelling between the apple and your eyes make the partly-submerged apple look crooked and misshapen.

Now try putting a pencil in a straight-sided glass that is half full of water. What do you see? Does it also look crooked when seen from the side? When looking from above, things in water appear shallower than they really are. The top of the water is flat but the area where it touches the glass is curved. A curved, refracting surface is a kind of lens.


This activity is adapted from page 315 of What Your Year 4 Child Needs to Know, which can be purchased here. Click below to see the related activities.

science owl
science owl