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CHILDREN'S SCIENTIFIC LABORATORY
With compass through magnetic fields. Children's Science Lab
Directory / Children's Science Lab Now there are almost no people left who will gratefully shake your hand for the story that the Earth is round, saying: "Thank you, friend, you will always hear something new." But why is she spinning? This question baffles not only the student. Their learned fathers also become thoughtful when the eternal rotation asks them this "why". "Probably magnetism," they say. So why? But... first about magnetism in general. Electromagnetic field from a nail and a file With a file or even a simple nail, you can. obtain well-marked magnetic fields. It is enough to wrap them with an insulated wire and let current flow through it. The electric current, passing through the coils, will create a field, and the core will sharply increase it. The very core of such a simple solenoid, be it a nail or a file, will become a magnet. But at the same time, a core magnet made from a nail will have a fundamental difference from a magnet made from a file. What do you think this difference is? This will be discussed below. But if you want to find the difference yourself, then do the following experiments. Wrap an insulated wire 0,1-0,4 mm thick around an ordinary nail. Connect one end of the winding to the flashlight battery (Fig. 1). Sprinkle small cloves on the table. Bring the head of the nail to the small studs, then attach the other end of the winding to the battery. Small nails will instantly stick to the head of the core nail. When turned off, the clove batteries will immediately fall.
Now let's make an artificial magnet from a file. On the emery wheel, grind off the notch from the planes of the file, cut off the necessary strip from it. Then the strip must be rubbed from the center to the ends - with the opposite poles of the magnets. A rigid steel strip can be artificially magnetized in another way - using a direct electric current. Wind a wire with good insulation on a steel plate, and then turn on the winding through the rheostat for a few seconds. Now the difference between a magnetized nail and a file will become apparent. In the first case, the core has magnetic properties only during the passage of current (along the turns), in the second case, a permanent magnet is obtained. A file, unlike a nail, will have residual magnetism. The reason lies in the high hardness of the file material. In a solid steel plate, the atoms of which it is composed are very "strongly" oriented. Therefore, they better retain their magnetic properties. By cutting the magnet in half, we get two identical magnets with different poles. By repeating this operation, we again get magnets with different poles. If we cut a magnet into microscopic particles, each of these particles would still have two poles: north (positive) and south (negative). This fact leads to the conclusion that the poles of a magnet do not exist separately, just as there are negative (electrons) and positive (protons) electrically charged particles. However, it is possible to make a magnet with the same poles at the ends. It is only necessary to rub the steel plate with the same poles, for example, north ones, leading them from the middle to the ends. Then the atoms will be arranged in the structure of the plate so that the north poles will go in one direction, and the south - in the other. The magnetic needle is located along the magnetic lines of force. The configuration of magnetic field lines is easy to capture with iron filings. After placing the glass with metal filings on the bar magnet, lightly tap on the glass. Each magnetized iron particle will be a small magnetic needle. Stretching along the lines of force of the field, they will reveal its configuration. During shaking, most of the sawdust will move to the poles. The equatorial part of the field will thin out. But electrically charged particles behave quite differently. If negatively and positively charged particles could be poured like sawdust on glass, then the charged particles would repel from the poles and concentrate in the equatorial zone of the magnetic field - in the form of a ring. But how can you see all this? Homemade galaxies Beams of charged particles, in particular electrons (beta particles), are produced in betatrons. In them, electrons are accelerated to almost the speed of light, and the devices themselves weigh tons, and sometimes hundreds of tons. And yet, almost every one of us is able to conduct an experiment with an electron beam using ordinary televisions. Indeed, in the TV tube, it is the electrons that hit the kinescope screen in rows, causing a glow. Take a stronger permanent magnet, bring its pole to the screen. The image on the screen will turn into a spiral resembling a galaxy. If the image is twisted to the right, then this means that the north pole of the magnet is brought to the screen. The south pole of the magnet forms a spiral twisted to the left. When the magnet approaches the screen, a dark ring will appear against it (if the magnet is cylindrical), and a bright point will remain in the very center, through which the electron flow continues to go to the pole. The dark spot shows that the magnetic poles repel electrons, direct them to the equator of the magnetic field and orbit around the magnet. The electrons are repelled by the north and south poles. Therefore, they are concentrated in the equatorial plane of the magnetic field in the form of a fairly flat ring, like the rings of the planet Saturn.
Taking the magnet by the end of the north pole with your right hand, bring it horizontally to the screen with its entire plane. The image on the screen will be bent by an arc - upwards above the equator of the magnetic field. Turn the magnet with the south pole to the right - the image on the screen will bend down. It can be seen from these experiments that electrons orbit counterclockwise in a magnetic field, if you look at the magnet from the north pole. If we are dealing with positively charged particles, then they, starting from the poles of the magnet, would go in the direction opposite to the direction of the electrons in orbit. And what will happen if the magnet is put on bearings and irradiated with a rather powerful electron beam? Probably, the magnet will begin to rotate: in the flow of electrons - clockwise, in the flow of protons - counterclockwise. The direction of rotation of the magnet will be opposite to the direction of twisting of the charged particles. And now let's remember that our Earth is a huge magnet, that a stream of protons falls on it from space. Now it is clear why we talked for a long time about magnetism before moving on to the promised explanation of the rotation of our planet. In one round dance The English scientist W. Gelbert believed that the Earth consists of a magnetic stone. Later it was decided that the Earth was magnetized from the Sun. Calculations disproved these hypotheses. They tried to explain the magnetism of the Earth by mass flows in its liquid metal core. However, this hypothesis itself relies on the hypothesis of the liquid core of the Earth. Many scientists believe that the core is solid and not at all iron. In 1891, the English scientist Schuster, apparently for the first time, tried to explain the magnetism of the Earth by its rotation around its axis. The well-known physicist P. N. Lebedev gave a lot of work to this hypothesis. He assumed that under the influence of centrifugal force, the electrons in atoms are displaced towards the surface of the Earth. From this, the surface must be negatively charged, this causes magnetism. But experiments with ring rotation up to 35 thousand revolutions per minute did not confirm the hypothesis - magnetism did not appear in the ring. In 1947, P. Bleket (England) suggested that the presence of a magnetic field in rotating bodies is an unknown law of nature. Blackett tried to establish the dependence of the magnetic field on the speed of rotation of the body. At that time, data were known on the rotation speed and magnetic fields of three celestial bodies - the Earth, the Sun and the White Dwarf - the star E78 from the constellation Virgo. The magnetic field of the body is characterized by its magnetic moment, the rotation of the body - by the angular momentum (taking into account the size and mass of the body). It has long been known that the magnetic moments of the Earth and the Sun are related to each other the same as their angular momenta. The E78 star observed this proportionality! Hence it became obvious that there is a direct connection between the rotation of celestial bodies and their magnetic field.
One got the impression that it was the rotation of the bodies that caused the magnetic field. Blacket tried to experimentally prove the existence of the law he proposed. For the experiment, a golden cylinder weighing 20 kg was made. But the most subtle experiments with the mentioned cylinder yielded nothing. The non-magnetic golden cylinder showed no signs of a magnetic field. Now the magnetic and angular momentums have been established for Jupiter, and also preliminary for Venus. And again, their magnetic fields, divided by angular momentum, are close to Blacket's number. After such a coincidence of the coefficients, it is difficult to attribute the matter to chance. So what - the rotation of the Earth excites a magnetic field, or the magnetic field of the Earth causes its rotation? For some reason, scientists have always believed that rotation has been inherent in the Earth since its formation. Is it so? Or maybe not! The analogy with our "television" experience raises the question: is it because the Earth rotates around its axis that it, like a large magnet, is in a stream of charged particles? The flow consists mainly of hydrogen nuclei (protons), helium (alpha particles). Electrons are not observed in the "solar wind", they are probably formed in magnetic traps at the moment of collisions of corpuscles and are produced in cascades in the zones of the Earth's magnetic field. Earth - electromagnet The connection between the magnetic properties of the Earth and its core is now quite obvious. Scientists' calculations show that the Moon does not have a fluid core, so it should not have a magnetic field either. Indeed, measurements using space rockets have shown that the Moon does not have an appreciable magnetic field around it. Interesting data were obtained as a result of observations of terrestrial currents in the Arctic and Antarctica. The intensity of terrestrial electric currents there is very high. It is tens and hundreds of times higher than the intensity in the middle latitudes. This fact indicates that the influx of electrons from the rings of the Earth's magnetic traps enters the Earth intensely through the polar caps in the zones of the magnetic poles, as in our experiment with the TV. At the moment of increased solar activity, terrestrial electric currents also increase. Now, probably, it can be considered as established that electric currents in the Earth are caused by the currents of the masses of the Earth's core and the influx of electrons into the Earth from space, mainly from its radiation rings. So, electric currents cause the Earth's magnetic field, and the Earth's magnetic field, in turn, obviously makes our Earth rotate. It is easy to guess that the speed of the Earth's rotation will depend on the ratio of negatively and positively charged particles captured by its magnetic field from the outside, and also born within the Earth's magnetic field. Author: I.Kirillov
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