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ENTERTAINING EXPERIENCES AT HOME
See the invisible. Physical experiments
Entertaining experiences at home / Physics experiments for children About four hundred years ago, skilled craftsmen in Italy and Holland learned how to make glasses. Following glasses, magnifiers were invented for examining small objects. It was very interesting and captivating: to suddenly see in all details some grain of millet or a fly leg! In our age, radio amateurs are building equipment that allows them to receive more and more remote stations. And three hundred years ago, opticians were addicted to grinding ever stronger lenses, allowing them to penetrate further into the world of the invisible. One of these amateurs was the Dutchman Anthony van Leeuwenhoek. The lenses of the best masters of that time were magnified only thirty to forty times. And Leeuwenhoek's lenses gave an accurate, clear image, magnified three hundred times! As if a whole world of miracles opened up before the inquisitive Dutchman. Leeuwenhoek dragged under the glass everything that came into his eyes. He was the first to see microorganisms in a drop of water, capillary vessels in the tail of a tadpole, red blood cells and dozens, hundreds of other amazing things that no one had suspected before him. But don't think that Leeuwenhoek had an easy time with his discoveries. He was a selfless man who devoted his whole life to research. His lenses were very uncomfortable, unlike today's microscopes. I had to rest my nose against a special stand so that during the observation the head was completely motionless. And so, resting against the stand, Leeuwenhoek spent sixty years! Modern microscopes give an increase of one and a half - two thousand times, and electronic ones - even 200 thousand times. Of course, you and I cannot make a real microscope. But we can build a magnifying glass a little like the one used by Leeuwenhoek! Cut out a plate from thin sheet brass, copper, zinc, or at least from tin from a can. Put this plate on a board and pierce a hole in it with a sewing needle. Perhaps you think that it is impossible to pierce a plate with a needle, that the needle will break? Yes, of course, it will break if you let it bend. The trick is to keep the needle from bending. To do this, pick up a long cork stopper. Drive the needle vertically into the cork. If it turns out that the cork is a little short and the eye of the needle protrudes, break it off. Then put two dominoes or two identical boards on the table so that there is very little space between them. Above this space, put a plate on the supports, and put a cork with a needle on it. If now you hit the cork with a hammer hard and abruptly, the needle will pierce the plate through and through!
It is interesting that this hole in itself, without any glass, already increases. Bring the plate to your very eye and look through the hole at least at the book page, but only from a distance of about two centimeters. With the naked eye, you can't see anything that close. And through the hole, the letters will seem very large, as if not in a book, but on a poster! In the same way, you can consider, for example, a small bug, impaled on a pin, a fly's foot, and you never know what else. There is only one condition: the observed object must be very brightly lit. It is best to hold it against the light or cast the light of a lamp on it using a mirror.
A small hole increases because the rays are also refracted at its edges, as in a lens. But you can insert a lens into this hole, and then its magnifying effect will be greatly enhanced. How to do it? Take a drop of pure water or vaseline oil on the tip of a pin and "plant" it in the hole. Of course, the plate must be held horizontally so that our liquid "lens" does not leak and lose its round shape. If the drop is small, add more liquid. So you can pick up a "lens" with a high magnification. It will only be very inconvenient to use it. The plate must be held motionless and horizontal, and the head very close to it and also completely motionless. Work a little with this "microscope", and you will understand what patience Leeuwenhoek had! Leeuwenhoek used one lens. But already in his time there were microscopes with two glasses. In them, the image that the first lens gave was viewed not directly with the eye, but through the second lens. And this second lens was taken weaker, so that it would be more convenient to attach the eye to it. So not only was it easier to see, but even once again an increase was obtained! True, in those days, microscopes with two lenses were still very imperfect. They magnified only a few tens of times and gave a poor, unsharp image. Leeuwenhoek "squeezed" much more out of his one lens. But gradually, two-lens microscopes were improved, and they far surpassed what the Leeuwenhoek lens gave. Our current microscopes came from them, in which there are no longer two lenses, but two groups of glasses: one facing the object of observation (objective), the other facing the eye (eyepiece). Author: Galpershtein L.Ya.
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