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ENTERTAINING EXPERIENCES AT HOME
The complexity of the world. Physical experiments
Entertaining experiences at home / Physics experiments for children When in school it comes to the branch of physics called "Optics", you will learn that light is a wave process. What are waves (for example, on water), of course, you know well. They probably heard about electromagnetic waves: after all, who was not interested in knowing where TV and radio programs get on TV screens or into radio loudspeakers. To the question: "How does it work?" - you were answered very briefly: "With the help of radio waves" (or electromagnetic waves). Radio waves are transmitted from a central television station or radio station and received by a television or receiver. So you know that electromagnetic waves exist. Light is also electromagnetic waves. But the length of light waves is much shorter than the length of radio waves. And the white color we see, so simple at first glance, is actually very complex. It consists of seven primary colors: red, orange, yellow, green, blue, indigo and violet. And each of these colors has its own wavelength. When all seven colors are present, the impression is white. Sometimes you can see all these colors separately: either in the sky in the form of a rainbow, or at home, somewhere on the wall, when a bright ray of the sun, refracted at the edge of the mirror, gives a bright, multi-colored stripe. There are several ways to observe such a strip, or spectrum, that is, a white beam decomposed into its component colors. For example, if you look against a bright light source at a long-playing gramophone record, holding it horizontally and pressing it to the bridge of your nose. The new phonograph record is especially capable of creating a beautiful "iris". Light waves, like any oscillations, can, under certain conditions, both add up and subtract. When waves of the same length are added, the light is amplified, and when they are subtracted from each other, the light is attenuated or disappears altogether. Now we will verify this. For the experiment, you need to make a fairly simple device. Take a piece of thick black paper and use a safety razor blade to make a three-centimeter cut in it. It turned out a very narrow gap - this is our device. This slit has the ability to add and subtract light waves. Look through it during the day at the sky. You will see many black parallel stripes along the gap. Black stripes - where there is no light. In those places of the gap where there is a black strip, the light waves seem to "ate" each other. It would be more accurate to say that light waves of the same length subtracted from each other and the light in this place disappeared: darkness formed - a small black stripe. Now look through this slit at a brighter light source - at the filament of a burning electric light bulb (turn the slit as far as possible along the hot filament). In addition to the black stripes, you will see a lot of iridescent threads on both sides of the light bulb filament. As you move away from the bright part, from the middle, these rainbow threads become dimmer. A narrow slit has the ability to add and subtract light waves, and also sort them into individual colors (that is, by wavelengths). Doing these experiments, adjust the width of the gap. It must be very narrow, extremely narrow. This is easily achieved by spreading the edges of the paper in different directions. By studying "Optics" you will learn in more detail what happens in such a narrow slit, you will find out why it has the ability to decompose light into its component colors. Thin films also have the ability to decompose light into all the colors of the rainbow. This refers to the thinnest films that can be found in nature or created with your own hands. For example, they are formed by soapy water when blowing bubbles, machine oil stains on wet asphalt and puddles, the surface of mother-of-pearl shells, consisting of the thinnest scales. Very beautiful films are obtained by spreading a drop of nail polish on the surface of the water. Pour clean water into a plate and drop a drop of varnish there: it will spread in a thin layer over the water. Make a ring out of wire (about six to eight centimeters in diameter) and, for convenience, a handle. Pry off the lacquer film with the ring and, tilting it slightly, remove the film. She will play with all the colors of the rainbow, resembling the wings of a dragonfly. Such a film can be stored for quite a long time. A beam of white light, falling on a thin film or flake, is partially reflected from it, and partially passes deep into and is reflected from its inner surface. Both of these reflections fall into our eyes. It is clear that both reflected beams are slightly different from each other: they have traveled different paths. The difference in path is, you guessed it, about twice the thickness of the film. When dealing with such small quantities as the wavelengths of light, the thickness of even the thinnest film still turns out to be huge and the path difference of the reflected rays is large. What happens to these two reflected beams? They add up, or rather, their waves add up and fall into our eyes no longer in the form of a white beam, but a beam of some color. The color depends on the thickness of the film (what is the path difference) "and on the angle at which we look at this film. So it turns out that the entire surface of the film shimmers with different colors of the rainbow. There is another way to get a rainbow - with a prism, a trihedral transparent prism. The ideal instrument for this experiment would, of course, be a glass prism. But it is unlikely that you will find anything similar to her at home. A transparent trihedral prism can also be made from a piece of plexiglass by working it with the appropriate tools and then sanding its surfaces. But it is unlikely that everyone can do this, so we will choose a different path: we will make a transparent trihedral prism from a simple material - water. Take a small, cheap mirror, you can round. Put it in the bottom of a small bowl. Pour water into it and tilt it, placing something under it. The surface of the water in the basin should form an angle of approximately 25° with the mirror (see illustration). Now we need to take care of the light source. The experiment is best done in the evening, in the dark, so that the rainbow that you get is clearly visible.
Use, for example, a flashlight for photographic work as a light source, replacing the red light filter with cardboard and making a slit in it a little narrower than the cardboard and one centimeter wide. It is only important that the slot is not at the level of the light bulb filament. If you do not have such a lantern, you can also use a table lamp with a lampshade that does not let light through. The results of the experiments will be somewhat different from each other, so we describe them separately. In the case when you use a flashlight, direct the light of the slit on the mirror in the water from the side where the mirror is immersed deeper (see figure). If you now look from above at the mirror, you will see an iridescent strip with bright colors of the spectrum. The light from the crack passed through the water, refracted in it, hit the mirror, reflected from it and left the water as a beam of colored rays. As mentioned earlier, light entering another inhomogeneous medium is refracted in it. But since light consists of different colors, and each color beam is refracted in its own way, in different ways, then as a result of such a trihedral prism (it doesn’t matter if it is glass or water, as in our experience), the light comes out decomposed into all the colors of the rainbow. If the experiment is carried out with a table lamp, then there is no gap, the lamp itself should create a rainbow bunny. Hold the lamp at a distance of about one meter from the mirror. Please note that the ceiling is not lit by a lamp, it is in the shade. A rainbow reflection from the mirror will appear on the shaded ceiling. By moving the lamp, you can achieve on the ceiling, as on the screen, the appearance of a beautiful spectrum. At other angles between the mirror and the surface of the water, the rainbow may appear not on the ceiling, but on the wall. If the wall is covered with wallpaper, you need to hang a sheet of white paper in the place where the rainbow hit. This experiment can be successfully carried out during the day, using, if you have a sunny side, the rays of the sun. It is necessary to create darkness in the room by hanging the windows. Leave a gap in one of the windows for the sun's rays. Each of you may have different conditions, so you yourself need to think about how to do the experiment under these conditions. Author: Rabiza F.V.
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