Refraction Activities
Bent Light
| Put a penny in the middle of a big mixing bowl. It might be wise to fix it there with Plasticine. Look along a line of sight, over the edge of the bowl. Keep still while somebody fills the bowl with water. (You could fix your eye position by peeping through a hole in a card, bent to stand upright.) As the bowl fills, the penny appears to swim into sight. |
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But the penny and your sight line are fixed. What has changed? Light reflected by the penny - which you were unable to see before - now comes into your line of sight. To do this, the light must bend. It bends towards your line of sight when it leaves the water. Underwater, as in air, light usually travels in straight lines.
Think about the penny trick. When you observe the penny while it is underwater, it appears to be higher than where you know it must be. Also, the depth of the water seems less. Water in a swimming pool is always deeper than it looks - so take care.
Stick Tricks
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The explanation of the penny trick will help you to understand how a stick that is partly dipped in water appears to be bent. |
| Try these light tricks with a stick and glass jar filled with water. The curved glass shapes the water into a magnifying lens. Lenses work by bending light. |
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More Evidence That Light Can Bend
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You need a rectangular plastic
lunchbox, or something similar, that is transparent. Fill the box with water. Stand it on
a sheet of paper. Rest a peashooter (minus its mouthpiece) behind the box, so that it
touches at an angle of about 50'. Look through a second peashooter tube from the opposite side of the box - through the water - at the first tube. Arrange the tube along which you are sighting so that you can see light coming to you from the far end of tube one. Let both tubes rest on the paper. |
Stand back and look down on the tubes through which the light "beam" came to your eye. The tubes are not in line. The light coming through the first tube must have bent when it entered the water and (assuming it travelled straight through the water) it must have bent again when it passed from the water into the second tube. When light bends like this it is said to be refracted.
A Fisherman's Secret
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Refraction is the secret of yet another mystery. Draw two equal fishes touching a line ruled on a paper. Rest the box of water over one of the fishes. Notice that the "underwater" fish looks higher up and a little further back than where you know it must be. (The second fish acts as a control, to help you make the comparison.) |
Headless soldier
| Stand a toy soldier up to its neck in water, inside a plastic box or an aquarium. To "behead" the soldier, look through the side of the container, but "at an angle". |
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You see light coming directly to you from the head, but light coming out from underwater is refracted and seems to be coming from an unlikely place.
The Broken Pencil in Water
You Need: • pencil |
Fill the glass nearly to the top with water. Place the pencil in the water so that it slants across the insdie of the glass. Notice the part of the pencil where it enters the water. it appears broken and slightly larger. This is becuse the light that shines on the upper part of the pencil first strikes the pencil then travels to your eyes through air andd the top part of the glass. This light is only reflected and not bent.
| The light that allows you to see the part of the pencil below the water
must travel through the water, the glass, and then the air to reach your eyes. the
light rays are bent. This slows the light rays just enough so that they reach your
eyes slightly after the ones from the part of the pencil above the waer. This
time difference is enough to distort the image. The distortion is called refraction. The part of the pencil below the water also appears larger. This is because the water and curvature of the glass magnify the image. |
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The Moving Coin
You Need: • cereal bowl |
Place the coin in the bowl at the edge where the bowl starts to slope upward. This will be a reference point. Look at the coin from an angle above the lip of the bowl. Position your head so that you can only see the outer edge of the coin, keep looking at the coin and very slowly pour water into the bowl. This coin will appear to move toward the centre of the bowl until it is in full view. Check to ensure that the coin hasn't moved by looking at the reference point.
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When there was no water in the bowl, the light travelled in a straight line from the coin to your eyes. As you sighted over the edge of the bowl, only the outer edge of the coin was reflecting light to your eyes. When water was added to the bowl, the light rays were bent, or refracted by the water. The angle of the bending was great enough to allow all of the light reflected from the coin to travel to your eyes.
