A Long Lens


This week we will see that you can do science experiments anytime, even while cleaning out the refrigerator. Well, to be honest, it distracted me from cleaning out the refrigerator, but eventually the job will get done. I
promise. I really do promise. To avoid cleaning your refrig.... I mean to try this experiment, you will need:

  • a long glass jar, like olives come in
  • water
  • a magnifying glass

Look in your refrigerator, and get that old jar of olives from the bottom shelf. Put the last few olives onto a plate. Add a few pickles, some cubes of cheese, some celery, and a few grapes, and you will have a nice snack to eat while you do this experiment.

Wash the olive jar and remove the label. You may have to let it soak in hot water to get the label off, which will give you time to enjoy your snack.

Fill a large bowl or dish pan with water. Place the jar under the water and turn it so all the air comes out. Still under water, put the lid on the jar. When you remove it from the water, there should not be any air bubbles inside. Dry the outside of the jar.


Print the following words on a sheet of paper. Print them neatly, just as they are here. If your handwriting is like mine, type the words, and print them with your printer.

HIDE MY BIKE

Yes, it is a strange thing to write, but soon you will understand. Place the olive jar over the words, with the side of the jar touching the paper. Reading through the jar, what do you see? You see the same words, maybe a bit bigger depending on your jar, but otherwise just the same.


Now comes the interesting part. Lift the olive jar a couple of inches off the paper, and read the words through the jar again. What happened? The words HIDE and BIKE look the same, but the word MY is upside down! Why?

To understand, we need to know a bit about lenses. Hold a magnifying glass a few inches above the words. Looking through the lens, the words look larger, and they are all right side up. Then try holding the magnifying glass about 2 feet in front of you and looking at your room through it. Everything is upside down and backwards. Quite a difference.


As light passes through the lens of the magnifying glass, it is bent. The light bends toward the center, so light from the top is bent downwards. Light from the bottom is bent upwards. Light from the right is bent to the left. Light from the left is bent to the right. As the light moves away from the lens, you reach a point where all the light comes together. You have seen that point if you have ever used a magnifying glass to burn a piece of paper. As the light passes that point, it spreads out again, but now if is reversed. Beyond the focal point, the light from the top is now at the bottom. The light from the right is now on the left. The image looks upside down and backwards.


Now, lets compare that with our olive jar. Holding the olive jar horizontally over the words, you will now see that you have a lens that is a cylinder instead of circle. It is curved on the top and bottom, but it does not curve inwards from the sides. The light from the top is bent downwards, and the light from the bottom is bent upwards, but the light on the left and right is not bent towards the center. As a result, when you move past the focal point,
the image is flipped upside down, but not reversed left to right. The words HIDE and BIKE are made up of letters that look the same upside down as they do right side up. That lets them look the same when you read them through the olive jar. The letters M, Y, and most of the other letters in the alphabet look different when they are upside down,

If you want a challenge, make a list of the letters that look normal though the olive jar. Can you write an entire sentence that looks right through your long lens? If you come up with a good one, email it to me. I'll post the best ones. Now I have to finish my snack, and get back to cleaning out the refrigerator.

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