Instruments for measuring environmental quality. How to study the atmosphere: description, methods and methods of research

Planet Earth is wrapped in an atmosphere like an invisible blanket. This shell protects the Earth, as well as all its inhabitants, from threats from space. It can also be argued that life on Earth is possible only due to the existence of an atmosphere.

Humanity has been interested in studying the air envelope of the planet for a long time, but instruments for measuring atmospheric indicators appeared relatively recently - only about four centuries ago. What are the ways to study the air envelope of the Earth? Let's take a closer look at them.

Study of the atmosphere

Every person relies on weather forecasts from the media. But before this information becomes known to the public, it must be collected through a variety of various methods. For those who are interested in how the atmosphere is studied, it will be important to know: the main instruments for studying it, which were invented in the 16th century, are a weather vane, a thermometer, and a barometer.

Now he is studying the air shell of the Earth. In addition to Russia, it includes many other countries. Since they study the atmosphere in our time with the help special equipment, WMO staff have developed special programs for data collection and processing. For this purpose, the most modern technologies are used.

Thermometers

Temperature is still measured using thermometers. Degrees are measured in Celsius. This system based on physical properties water. At zero degrees Celsius it becomes solid state, at 100 - into gaseous.

This system is named after a scientist from Sweden. He proposed measuring temperature using this method in 1742. Despite technological advances, many places still use mercury thermometers.

Precipitation gauge

Information about how the atmosphere is studied will be of interest to both schoolchildren and adults. For example, it is interesting to know that the amount of precipitation is measured by meteorologists using a rain gauge. This is a device with which you can measure both the amount of liquid and solid precipitation.

This method of studying the atmosphere appeared in the 70s of the last century. The rain gauge consists of a bucket that is mounted on a pole and surrounded by a windbreak. The device is placed on flat areas; the optimal installation option is in a place surrounded by houses or trees. If the amount of precipitation exceeds 49 mm in 12 hours, the rain is considered heavy. For snow, this term is applied if 19 mm falls during the same period of time.

Measuring wind speed and direction

To measure wind speed, a device called an anemometer is used. It is also used to study the speed of directed air flows.

Air speed is one of the most important indicators atmosphere. In order to measure wind speed and direction, special ultrasonic sensors (anemormbometers) are used. A weather vane is usually installed next to the anemometer. Also, near airfields, bridges and other places where strong winds can pose a danger, special cone-shaped bags made of striped fabric are usually installed.

Barometers

We looked at what instruments and how to study the atmosphere. However, a review of all methods for studying it would be incomplete without mentioning the barometer - a special device with which you can determine the strength of atmospheric pressure.

The idea of a barometer was proposed by Galileo, although it was realized by his student E. Torricelli, who first proved the fact of atmospheric pressure. Barometers that measure pressure atmospheric column, allow you to make a weather forecast. In addition, these devices are also used as altimeters, since air pressure in the atmosphere depends on altitude.

Why does air press on the surface of the Earth? Air molecules, like all other material bodies, are attracted to the surface of our planet by the force of gravity. The fact that air has weight was demonstrated by Galileo, and this pressure was invented by E. Torricelli.

Professions that study the atmosphere

The study of the Earth's air envelope is carried out mainly by representatives of two professions - weather forecasters and meteorologists. What is the difference between these two professions?

Meteorologists take part in various expeditions. Their work often takes place at polar stations, high mountain plateaus, as well as airfields and ocean liners. The meteorologist cannot distract himself for a minute from his observations. No matter how insignificant the fluctuations may seem, he must enter them in a special journal.

Forecasters differ from meteorologists in that they predict the weather by analyzing physiological processes. By the way, the term “forecaster” comes from the ancient Greek language and is translated as “on-site observer.”

Who studies the atmosphere?

To make a weather forecast, it is necessary to use information collected from several points around the planet simultaneously. Air temperature is studied atmospheric pressure, as well as wind speed and strength. The science that studies the atmosphere is called meteorology. It examines the structure and all processes occurring in the atmosphere. There are special meteorological centers all over the Earth.

Schoolchildren often need information about the atmosphere, meteorology and meteorologists. Most often they have to explore this question in 6th grade. How is the atmosphere studied, and what specialists are involved in collecting and processing data about changes in it?

The atmosphere is studied by meteorologists, climatologists and aerologists. Representatives of the latter profession are studying various indicators of the atmosphere. Marine meteorologists are specialists who observe the behavior of air masses over the world's oceans. Atmospheric scientists provide information about the atmosphere to maritime transport.

Agricultural enterprises also need this data. There is also such a branch of atmospheric science as radiometeorology. And in recent decades, another area has developed - satellite meteorology.

Why is meteorology needed?

In order for a correct weather forecast to be compiled, information not only must be collected from different corners globe, but also correctly processed. How more information a meteorologist (or other researcher) has, the more accurate the result of his work will be. Currently all data is processed using computer technology. Meteorological information is not only stored in a computer, but is also used to create weather forecasts for the near future.

We know that conductors carrying currents interact with each other with some force (§ 37). This is explained by the fact that each current-carrying conductor is affected by the magnetic field of the current of the other conductor.

At all a magnetic field acts with some force on any current-carrying conductor located in this field.

Figure 117, a shows a conductor AB suspended on flexible wires that are connected to a current source. The conductor AB is placed between the poles of an arc-shaped magnet, i.e. it is in a magnetic field. When the electrical circuit is closed, the conductor begins to move (Fig. 117, b).

Rice. 117. Action magnetic field to a current-carrying conductor

The direction of movement of the conductor depends on the direction of the current in it and on the location of the poles of the magnet. In this case, the current is directed from A to B, and the conductor deviates to the left. When the direction of current is reversed, the conductor will move to the right. In the same way, the conductor will change the direction of movement when the location of the magnet poles changes.

The rotation of a current-carrying conductor in a magnetic field is of practical importance.

Figure 118 shows a device that can be used to demonstrate such a movement. In this device, a lightweight rectangular ABCD frame is mounted on a vertical axis. A winding consisting of several dozen turns of wire coated with insulation is laid on the frame. The ends of the winding are connected to metal half-rings 2: one end of the winding is connected to one half-ring, the other to the other.

Rice. 118. Rotation of a frame with current in a magnetic field

Each half-ring is pressed against a metal plate - brush 1. The brushes serve to supply current from the source to the frame. One brush is always connected to the positive pole of the source, and the other to the negative pole.

We know that the current in the circuit is directed from the positive pole of the source to the negative, therefore, in the parts of the frame AB and DC it has opposite direction, so these parts of the conductor will move in opposite directions and the frame will rotate. When the frame is rotated, the half rings attached to its ends will turn with it and each will press against the other brush, so the current in the frame will change direction to the opposite. This is necessary so that the frame continues to rotate in the same direction.

Rotation of a coil with current in a magnetic field is used in the device electric motor.

In technical electric motors, the winding consists of large number turns of wire. These turns are placed in grooves (slots) made along the side surface of the iron cylinder. This cylinder is needed to enhance the magnetic field. Figure 119 shows a diagram of such a device, it is called engine anchor. In the diagram (it is shown in a perpendicular section), the turns of the wire are shown in circles.

Rice. 119. Engine armature diagram

The magnetic field in which the armature of such a motor rotates is created by a strong electromagnet. The electromagnet is supplied with current from the same current source as the armature winding. The motor shaft, running along the central axis of the iron cylinder, is connected to a device that is driven by the motor to rotate.

DC motors have found particularly wide application in transport (electric locomotives, trams, trolleybuses).

There are special non-sparking electric motors that are used in pumps for pumping oil out of wells.

In industry, AC motors are used (you will study these in high school).

Electric motors have a number of advantages. With the same power they are smaller in size than heat engines. During operation, they do not emit gases, smoke or steam, which means they do not pollute the air. They do not need a supply of fuel and water. Electric motors can be installed in a convenient place: on a machine, under the floor of a tram, on the bogie of an electric locomotive. It is possible to produce an electric motor of any power: from a few watts (in electric shavers) to hundreds and thousands of kilowatts (in excavators, rolling mills, ships).

Coefficient useful action powerful electric motors reaches 98%. No other engine has such high efficiency.

Jacobi Boris Semyonovich (1801-1874)
Russian physicist. He became famous for the discovery of electroplating. He built the first electric motor and a telegraph machine that printed letters.

One of the world's first electric motors suitable for practical use was invented by the Russian scientist Boris Semenovich Jacobi in 1834.

Questions

How to show that a magnetic field acts on a current-carrying conductor located in this field?
Using Figure 117, explain what determines the direction of movement of a conductor carrying current in a magnetic field.
What device can be used to rotate a current-carrying conductor in a magnetic field? What device in the frame is used to change the direction of the current every half turn?
Describe the structure of a technical electric motor.
Where are they used? electric motors? What are their advantages over thermal ones?
Who and when invented the first electric motor suitable for practical use?

Exercise

For waves in the meter and decimeter ranges, the ionosphere is transparent. Communication on these waves is carried out only at a line of sight distance. For this reason, transmitting television antennas are placed on high television towers, and for television broadcasting over long distances it is necessary to build relay stations, receiving and then transmitting the signal.

And yet, at present, it is waves with a length of less than a meter that are used for long-distance radio communications. Artificial Earth satellites come to the rescue. Satellites used for radio communications are placed into geostationary orbit, the period of revolution of which coincides with the period of revolution of the Earth around its axis (about 24 hours). As a result, the satellite rotates with the Earth and thus hovers over a certain point on the Earth located at the equator. The radius of the geostationary orbit is about 40,000 km. Such a satellite receives a signal from Earth and then relays it back. Satellite television has already become quite common; in any city you can see “dishes” - antennas for receiving a satellite signal. However, in addition to television signals, a lot of other signals are transmitted via satellites, in particular Internet signals, and communication is carried out with ships located in the seas and oceans. This connection turns out to be more reliable than short-wave communication. Features of radio wave propagation are illustrated in Fig. 3.

All radio waves are divided into several ranges depending on their length. The names of the bands, properties of radio wave propagation and characteristic areas of use of waves are given in the table.

Radio wave bands
Wave range	Wavelengths	Spread Properties	Usage
		They bend around the surface of the Earth and obstacles (mountains, buildings)	Broadcasting
		Broadcasting, radio communications
Short		Straight propagation, reflected from the ionosphere.
Ultra short	1 – 10 m (meter)	Straight-line propagation, passing through the ionosphere.	Radio broadcasting, television broadcasting, radio communications, radar.
1 – 10 dm (decimeter)
1 – 10 cm (centimeter)
1 – 10 mm (mm)

The generation of radio waves occurs as a result of the movement of charged particles with acceleration. A wave of this frequency is generated at oscillatory movement charged particles with this frequency. When free charged particles are exposed to radio waves, an alternating current of the same frequency as the frequency of the wave appears. This current can be detected by a receiving device. Radio waves of different ranges propagate differently near the Earth's surface.

1. · What frequency corresponds to the shortest and longest radio waves?

2. * State a hypothesis about what may determine the limit of the lengths of radio waves reflected by the ionosphere.

3. · What ranges of waves coming to us from space can we receive with ground-based receivers?

§26. Use of radio waves.

(Lesson-lecture).

Here, there is a radio, but there is no happiness.

I. Ilf, E. Petrov

How can information be transmitted using radio waves? What is the basis for the transmission of information using artificial Earth satellites? What are the principles of radar, and what capabilities does radar provide?

Radio communication. Radar. Wave modulation.

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Alexander Stepanovich Popov (1859 - 1906) - famous Russian physicist, inventor of radio. Carried out the first experiments on practical application radio waves In 1986, he demonstrated the first radiotelegraph.

Improved designs of radio transmitters and radio receivers were developed by the Italian Marconi, who in 1921 managed to establish regular communications between Europe and America.

Principles of wave modulation.

The main task assigned to radio waves is the transmission of some information over a distance. A monochromatic radio wave of a certain length is a sinusoidal oscillation of the electromagnetic field and does not carry any information. In order for such a wave to carry information, it must be changed in some way or, in scientific terms, modulate(from Latin modulatio - dimension, dimension). The simplest radio wave modulation used in the first radiotelegraphs, for which Morse code was used. Using a key, the radio transmitters were turned on for a longer or shorter time. Long spaces corresponded to the “dash” sign, and short spaces corresponded to the “dot” sign. Each letter of the alphabet was associated with a certain set of dots and dashes, which came with a certain interval. In Fig. Figure 1 shows a graph of the oscillations of the wave transmitting the “dash-dot-dot-dash” signal. (Note that in a real signal, one dot or dash fits significantly larger number fluctuations).

Naturally, it was impossible to transmit voice or music with such a signal, so later they began to use other modulation. As you know, sound is a pressure wave. For example, a pure sound corresponding to the note A of the first octave corresponds to a wave, the pressure of which varies according to a sinusoidal law with a frequency of 440 Hz. Using a device - a microphone (from the Greek micros - small, phone - sound), pressure fluctuations can be converted into an electrical signal, which is a change in voltage with the same frequency. These oscillations can be superimposed on the oscillation of a radio wave. One of these modulation methods is shown in Fig. 2. Electrical signals corresponding to speech, music, and also images have more complex look, however, the essence of modulation remains unchanged - the amplitude envelope of the radio wave repeats the shape of the information signal.

Later, various other modulation methods were developed, in which not only the amplitude of the wave changes, as in Figures 1 and 2, but also the frequency, which made it possible to transmit, for example, a complex television signal, information-carrying about the image.

Currently, there is a tendency to return to the original “dots” and “dashes”. The fact is that any audio and video information can be encoded as a sequence of numbers. This is exactly the type of encoding that is carried out in modern computers. For example, an image on a computer screen consists of many dots, each of which glows in a different color. Each color is coded with a specific number, and thus the entire image can be represented as a sequence of numbers corresponding to points on the screen. In a computer, all numbers are stored and processed in the binary system of units, that is, the two digits 0 and 1 are used. Obviously, these numbers are similar to the dots and dashes of Morse code. Signals encoded in digital format have many advantages - they are less susceptible to distortion during radio transmission and are easily processed by modern electronic devices. That is why modern mobile phones, as well as the transmission of images using satellites, use a digital format.

Most of you have probably tuned your radios or televisions to some program, some of you have used a mobile phone connection. Our airwaves are filled with a wide variety of radio signals, and their number is constantly increasing. Aren't they "cramped" there? Are there any restrictions at all on the number of simultaneously operating radio and television transmitters?

It turns out that there are restrictions on the number of simultaneously operating transmitters. The fact is that when an electromagnetic wave carries any information, it is modulated by a certain signal. Such a modulated wave can no longer be associated with a strictly defined frequency or length. For example, if a wave A in Fig. 2 has a frequency w, lying in the radio wave range, and the signal b has a frequency W, lying in the range of sound waves (from 20 Hz to 20 kHz), then the modulated wave V actually represents three radio waves with frequencies w-W, w And w+W. The more information a wave contains, the larger frequency range it occupies. When transmitting sound, a range of approximately 16 kHz is sufficient; a television signal already occupies a range of approximately 8 MHz, that is, 500 times more. That is why the transmission of a television signal is possible only in the range of ultrashort (meter and decimeter) waves.

If the signal bands of two transmitters overlap, then the waves of these transmitters interfere. Interference causes interference when receiving waves. So that the transmitted signals do not influence each other, that is, so that the transmitted information is not distorted, the bands occupied by radio stations should not overlap. This places a limit on the number of radio transmitting devices operating in each band.

Radio waves can be used to transmit various information(sound, image, computer information), for which it is necessary to modulate the waves. A modulated wave occupies a certain frequency band. To prevent the waves of different transmitters from interfering, their frequencies must differ by a value greater than the frequency band.

Principles of radar.

Another important application of radio waves is radar, which is based on the ability of radio waves to be reflected from various objects. Radar allows you to determine the location of an object and its speed. For radar, waves of the decimeter and centimeter ranges are used. The reason for this choice is very simple: longer waves, due to the phenomenon of diffraction, bend around objects (airplanes, ships, cars), practically without being reflected from them. In principle, radar problems can be solved using electromagnetic waves in the visible range of the spectrum, that is, by visual observation of an object. However, visible radiation is delayed by atmospheric components such as clouds, fog, dust, and smoke. For radio waves, these objects are completely transparent, which allows the use of radar in all weather conditions.

To determine the location, you need to determine the direction to the object and the distance to it. The problem of determining the distance is solved simply. Radio waves travel at the speed of light, so the wave reaches an object and returns back in a time equal to twice the distance to the object divided by the speed of light. The transmitting device sends a radio pulse towards the object, and the receiving device, using the same antenna, receives this pulse. The time between transmission and reception of a radio pulse is automatically converted into distance.

To determine the direction to an object, highly directional antennas are used. Such antennas form a wave in the form of a narrow beam, so that the object falls into this beam only at a certain location of the antenna (the action is similar to the beam of a flashlight). During the radar process, the antenna is “rotated” so that the wave beam scans a large area of space. The word “rotates” is put in quotes because in modern antennas no mechanical rotation occurs; the direction of the antenna changes electronically. The principle of radar is illustrated in Fig. 3.

Radar makes it possible to set the distance to an object, the direction to the object and the speed of the object. Due to the ability of radio waves to travel freely through clouds and fog, radar techniques can be used in all weather conditions.

1. ○ What is the length of radio waves used for communication?

2. ○ How to “make” a radio wave carry information?

3. ○ How is the number of radio stations on the air limited?

4. · Assuming that the transmission frequency must be 10 times the frequency width occupied by the signal, calculate the minimum wavelength for transmission of a television signal.

5. * How can you determine the speed of an object using radar?

§ 27.Principles of operation of mobile telephony.

(Workshop lesson)

If Edison had such conversations, the world would never have seen a gramophone or a telephone.

I. Ilf, E. Petrov

How does mobile telephony work? What elements are included in a mobile telephone and what is their functional purpose? What are the prospects for the development of mobile telephony?

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WAY OF LIFE.

1. When using a mobile phone, there is constant radiation of radio waves in the immediate vicinity of the brain. Currently, scientists have not reached a consensus on the degree of influence of such radiation on the body. However, you should not have excessively long conversations on your mobile phone!

2. Mobile phone signals may interfere with various electronic devices, such as navigation devices. Some airlines prohibit the use of mobile phones during flights or during certain times of the flight (take-off, landing). If such prohibitions exist, follow them, it is in your interests!

3. Some elements of the mobile device, such as the liquid crystal display, may deteriorate when exposed to bright sun rays or high temperature. Other components, such as the electronic circuitry that converts signals, can deteriorate when exposed to moisture. Protect your mobile phone from such harmful influences!

Answer to task 1.

Compared to conventional telephone communication, mobile telephone communication does not require the subscriber to connect to a wire stretched to the telephone exchange (hence the name - mobile).

Compared to radio communication:

1. Mobile telephony allows you to contact any subscriber who has a mobile telephone or is connected to a wired telephone exchange in almost any area of the globe.

2. The transmitter in a mobile handset should not have high power, and therefore can be small in size and weight.
Answer to task 2. Ultrashort waves should be used for mobile communications.
Answer to task 3.

Answer to task 4. The telephone exchange must include devices that receive, amplify and transmit electromagnetic waves. Since the radio waves used travel over line-of-sight distances, it is necessary to have a network of relay stations. To communicate with other telephone exchanges located in distant regions, it is necessary to have connections to the long-distance and international networks.

Answer to task 5. The device must contain information input and output devices, a device that converts an information signal into a radio wave and back the radio wave into an information signal.
Answer to task 6. First of all, when using the phone, we transmit and perceive sound information. However, the device can also give us visual information. Examples: the phone number on which they call us, the phone number of our friend, which we have entered into the memory of our phone. Modern devices capable of perceiving video information, for which a video camera is built into them. Finally, when transmitting information, we also use such a sense as touch. To dial a number, we press buttons that contain numbers and letters.
Answer to task 7. Entering audio information – microphone, audio information output – telephone, input of video information – camcorder, output of video information – display, as well as buttons for entering information in the form of letters and numbers.
Answer to task 8.

(the dotted frame in the figure means that this device is not necessarily included in the mobile phone device).

§28. Geometric optics and optical instruments.

(Lesson-lecture).

Then, sparing neither labor nor expense, I succeeded in making an instrument so perfect that, when viewed through it, objects appeared almost a thousand times larger and more than thirty times closer than those seen naturally.

Galileo Galilei.

How are light phenomena considered from the point of view of geometric optics? What are lenses? What devices are they used in? How is visual magnification achieved? What devices allow you to achieve visual magnification? Geometric optics. Focal length of the lens. Lens. CCD matrix. Projector. Accommodation. Eyepiece.

Elements of geometric optics. Lens. Focal length of the lens. The eye as an optical system. Optical instruments . (Physics 7-9 grades). Natural Science 10, § 16.

Geometric optics and lens properties.

Light, like radio waves, is electromagnetic wave. However, the wavelength of visible radiation is several tenths of a micrometer. Therefore, wave phenomena such as interference and diffraction practically do not appear under normal conditions. This, in particular, led to the fact that the wave nature of light for a long time was not known, and even Newton assumed that light was a stream of particles. It was assumed that these particles move from one object to another in a straight line, and the flows of these particles form rays that can be observed by passing light through a small hole. This review is called geometric optics, in contrast to wave optics, where light is treated as a wave.

Geometric optics made it possible to substantiate the laws of light reflection and light refraction at the boundary between various transparent substances. As a result, the properties of lenses that you studied in the physics course were explained. It was with the invention of lenses that the practical use of the achievements of optics began.

Let us remember how an image is constructed in a thin converging lens (see Fig. 1).

An object is represented as a collection of luminous points, and its image is built point by point. To build an image of a point A you need to use two beams. One ray goes parallel to the optical axis, and after refraction in the lens passes through the focus F'. The other ray passes through the center of the lens without being refracted. The point at the intersection of these two rays A' and will be the image of a point A. The rest of the arrow points ending at A are constructed in a similar way, resulting in an arrow with the end at the point A'. Note that rays have the property of reversibility, therefore, if the source is placed at a point A’ , then its image will be at the point A.

Distance from source to lens d related to the distance from the image to the lens d¢ ratio: 1/ d + 1/d¢ = 1/f, Where f – focal length, that is, the distance from the focal point of the lens to the lens. The image of an object can be either reduced or enlarged. The increase (decrease) coefficient is easy to obtain based on Fig. 1 and similarity properties of triangles: G = d¢ /d. From the last two formulas we can derive the following property: the image is reduced if d>2f(in this case f< d¢ < 2f). From the reversibility of the ray path it follows that the image will be enlarged if f< d< 2f(in this case d¢ > 2f). Note that sometimes it is necessary to significantly enlarge the image, then the object must be placed at a distance from the lens a little further than the focus, the image will be at a great distance from the lens. On the contrary, if you need to significantly reduce the image, then the object is placed at a large distance from the lens, and its image will be slightly further than the focal point from the lens.

Lenses in various devices.

The described property of lenses is used in various devices where collecting lenses are used as lenses. Strictly speaking, any high-quality lens consists of a system of lenses, but its action is the same as that of a single converging lens.

Devices that magnify images are called projectors. Projectors are used, for example, in cinemas, where a film image measuring a few centimeters is enlarged to a screen size of several meters. Another type of projector is multimedia projectors. In them, a signal coming from a computer, VCR, or video disc recorder forms a small image, which is projected through a lens onto a large screen.

Much more often it is necessary to reduce, rather than enlarge, the image. This is what lenses in cameras and video cameras are used for. An image of several meters, for example an image of a person, is reduced to a size of several centimeters or several millimeters. The receiver where the image is projected is photographic film or a special matrix of semiconductor sensors ( CCD matrix), converting the video image into an electrical signal.

Image reduction is used in the production of microcircuits used in electronic devices, particularly computers. The elements of microcircuits - semiconductor devices, connecting wires, etc. - have dimensions of several micrometers, and their number on a silicon wafer with dimensions of the order of a centimeter reaches several million. Naturally, it is impossible to draw so many elements of such a scale without reducing it using a lens.

Lenses that reduce images are used in telescopes. Objects such as galaxies with dimensions of millions of light years “fit” on a film or CCD matrix with dimensions of several centimeters.

Concave mirrors are also used as lenses in telescopes. The properties of a concave mirror are in many ways similar to the properties of a converging lens, only the image is created not behind the mirror, but in front of the mirror (Fig. 2). It is like a reflection of the image received by the lens.

Our eye also contains a lens - a lens, which reduces the objects we see to the size of the retina - a few millimeters (Fig. 3).

To make the image sharp, special muscles change the focal length of the lens, increasing it when the object approaches and decreasing it when it moves away. The ability to change focal length is called accommodation. A normal eye is able to focus images for objects further than 12 cm from the eye. If the muscles are not able to reduce the focal length of the lens to the required value, the person does not see close objects, that is, he suffers from farsightedness. The situation can be corrected by placing a converging lens (glasses) in front of the eye, the effect of which is equivalent to reducing the focal length of the lens. The opposite vision defect, myopia, is corrected using a diverging lens.

Devices that provide visual magnification.

Using the eye, we can only estimate the angular dimensions of an object (see § 16 Natural Science 10). For example, we can cover the image of the Moon with a pinhead, that is, the angular dimensions of the Moon and the pinhead can be made the same. Visual magnification can be achieved either by bringing the object closer to the eye, or by somehow enlarging it at the same distance from the eye (Fig. 4).

Trying to look at some small object, we bring it closer to the eye. However, with a very close approach, our lens cannot cope with its work; the focal length cannot decrease so that we can view the object, for example, from a distance of 5 cm. The situation can be corrected in the same way as with farsightedness, by placing a converging lens in front of the eye. A lens used for this purpose is called magnifying glass. The distance from which it is convenient for the normal eye to view a small object is called the distance best vision. Usually this distance is taken to be 25 cm. If a magnifying glass allows you to view an object, for example, from a distance of 5 cm, then a visual magnification of 25/5 = 5 times is achieved.

How to get a visual magnification, for example, of the Moon? Using a lens, you need to create a reduced image of the Moon, but close to the eye, and then examine this image through a magnifying glass, which in this case is called eyepiece. This is exactly how the Kepler tube works (see § 16 Natural Science 10).

Visual enlargement, for example, of a plant or animal cell is obtained in a different way. The lens creates a magnified image of the object close to the eye, which is viewed through the eyepiece. This is exactly how a microscope works.

Lenses and lens systems are used in many devices. The lenses of the devices allow you to obtain both enlarged and reduced images of the object. Visual enlargement is achieved by increasing the angular size of an object. To do this, use a magnifying glass or eyepiece in a system with a lens.

1. · What property of rays is the action of lenses based on?

2. * Based on the method of constructing an image in a converging lens, explain why when the distance between the object and the eye changes, the focal length of the lens should change?

3. · In the microscope and Kepler tube, the image appears upside down. Which lens, objective or eyepiece reverses the image?

§ 29. The principle of operation of glasses.

(Workshop lesson).

The monkey's eyes have become weak in old age,

But she heard from people,

That this evil is not so big a hand,

You just have to get glasses.

What happens during eye accommodation? What is the difference between normal, nearsighted and farsighted eyes? How does a lens correct a vision defect?

Lens. Focal length of the lens. The eye as an optical system. Optical instruments . (Physics grades 7-9). Visual impairment. (Biology, basic school).

Purpose of the work: Using a multimedia program, explore the functioning of the eye lens in normal, nearsighted and farsighted vision. Explore how vision defects are corrected using a lens.

Equipment: Personal computer, multimedia disk (“Open Physics”).

Work plan: Performing the task sequentially, explore the possibilities of accommodation of a normal, myopic and farsighted eye. To study the accommodation of myopic and farsighted eyes in the presence of a lens in front of the eye. Select a lens for the appropriate eye.

You already know that vision defects such as myopia and farsightedness are associated with the inability, through the work of the eye muscles, to give the lens of the eye optimal curvature. With myopia, the lens remains too convex, its curvature is excessive, and, accordingly, the focal length is too short. The opposite occurs with farsightedness.

Recall that instead of focal length, another lens can be used to characterize a lens. physical quantity– optical power. Optical power is measured in diopters and is defined as the reciprocal of focal length: D = 1/f(1 diopter = 1/1m). The optical power of the diverging lens has negative value. The optical power of the lens is always positive. However, for a nearsighted eye the optical power of the lens is too great, and for a farsighted eye it is too small.

The action of glasses is based on the property of lenses, according to which the optical powers of two closely placed lenses are added (taking into account the sign).

Task 1. Examine the functioning of a normal eye without a lens. You are offered three accommodation options: normal - for the distance of best vision, far - for an infinitely large distance, and automatic, in which the eye adjusts the lens to a given distance. By changing the distance to the object, observe the moments when the eye is focused. Where is the image focused inside the eye in this case? What does the best vision distance correspond to in this program?

Task 2. Explore the effect of a magnifying glass. Set the normal eye to normal accommodation. Place a converging lens with the highest possible optical power in front of your eye. Find the distance at which the eye is focused. Using the material from the previous paragraph, determine how many times does this magnifying glass magnify?

Task 3. Repeat task 1 for the nearsighted and farsighted eyes. Where are the rays focused when the eye is not focused?

Task 4. Choose glasses for nearsighted and farsighted eyes. To do this, set automatic eye accommodation. Select a lens so that the eye is focused as the distance changes from the distance of best vision (25 cm) to infinity. What are the limits of the optical powers of the lenses at which the glasses for the “eyes” given in the program can successfully perform their functions?

Task 5. Try to achieve the optimal result for myopic and farsighted eyes, when with the selected lens the eye is focused at distances from infinity to the minimum possible.

Rays from distant objects, after passing through the lens of a myopic eye, are focused in front of the retina, and the image becomes blurry. To correct this, glasses with diverging lenses are required. Rays from close objects, after passing through the lens of a far-sighted eye, are focused behind the retina, and the image becomes blurred. To correct this, glasses with converging lenses are required.

§ 25. Electric power and ecology.

(Lesson-conference).

It has occurred to me more than once that working in hydraulic engineering construction is like war. In war you don’t have to yawn, otherwise you will be knocked over, and here you have to work continuously - the water comes on you.

What are the main components and principles of operation of a modern combined heat and power plant (CHP)? What are the main components and operating principle of a hydroelectric power station (HPP)? What is the impact on environmental situation can provide construction of thermal power plants and hydroelectric power stations?

Purpose of the conference: Familiarize yourself with the operation of the most common types of power plants, such as thermal power plants and hydroelectric power stations. Understand what impact the construction of these types of power plants can have on the environment.

Conference plan:

1. Construction and operation of a modern thermal power plant.

2. Construction and operation of a modern hydroelectric power station.

3. Power plants and ecology.

Assessing the historical past of our country, it should be recognized that it was the rapid breakthrough in the field of electric power that allowed as soon as possible turn an agricultural power into an industrial one developed country. Many rivers were “conquered” and forced to provide electricity. Only at the end of the 20th century did our society begin to analyze at what cost this breakthrough was achieved, at what cost? human resources, at the cost of any changes in nature. There are always two sides to any coin, and educated person must see and compare both sides.

Message 1. Factory of electricity and heat.

Combined heat and power plants are one of the most common producers of electricity. The main mechanism of a thermal power plant is a steam turbine that drives an electricity generator. The most appropriate is the construction of a thermal power plant in major cities, since the steam exhausted in the turbine enters the city’s heating system and supplies our homes with heat. The same steam heats hot water coming into our homes.

Message 2. How does a hydroelectric power station work?

Hydroelectric power plants are the most powerful producers of electricity. Unlike thermal power plants, hydroelectric power plants operate on renewable energy resources. It may seem that hydroelectric power is “given for free.” However, hydroelectric power plants are very expensive hydraulic structures. The cost of building a hydroelectric power station varies. The fastest payback is for power plants built on mountain rivers. The construction of hydroelectric power stations on lowland rivers requires, among other things, taking into account changes in the landscape and the withdrawal of quite large areas from industrial and agricultural use.

Message 3. Power plants and ecology.

Modern society requires a large amount of electricity. The production of such a volume of electricity is inevitably associated with the transformation of the nature around us. Minimizing negative consequences is one of the tasks that arise when designing power plants. But, first of all, it is necessary to understand the negative impact of powerful electricity production installations on nature.

Burning large quantity fuel can, in particular, cause phenomena such as acid rain, as well as chemical pollution. It would seem that hydroelectric power plants, in which nothing is burned, should not have a negative impact on nature. However, the construction of lowland hydroelectric power stations is always associated with the flooding of vast territories. Many of the environmental consequences of such flooding, carried out in the mid-20th century, are only now beginning to be felt. By blocking rivers with dams, we inevitably interfere with the lives of the inhabitants of reservoirs, which also has negative consequence. There is, for example, an opinion that all the electricity generated by the Volga hydroelectric power stations is not worth the losses associated with a decrease in the sturgeon catch.

Sources of information.

1. Children's encyclopedia.

2. Kirillin history of science and technology. - M.: Science. 1994.

3. Vodopyanov consequences of NPT. Minsk: Science and Technology, 1980.

5. Non-traditional energy sources. - M: Knowledge, 1982.

6., Skalkin aspects of environmental protection. - L.: Gidrometeoizdat, 1982.

7. Nikitin - technical progress, nature and man. - M: Nauka 1977.

8. , Spielrain. Problems and prospects. - M: Energy, 1981.

9. Physics and scientific and technological progress / Ed. , .- M: Education, 19888.

10.Energy and security environment/ Ed. and others - M.: Energy, 1979.

Modern power plants are complex engineering structures. They are necessary for existence modern society. However, their construction must be carried out in such a way as to minimize damage to nature.

During the operation of buildings, situations inevitably arise in which it is necessary to search for the locations of hidden wires and cables. These situations may include replacements, repairs to wiring faults, the need to refurbish or remodel the premises, or the need to install hanging furniture or equipment. A hidden wiring finder helps you quickly find wires without destroying walls. What is such a device, and what types of finders exist?

Hidden wiring

With a hidden installation method, detecting wiring under thick brick or concrete is not an easy task for a person who is encountering such a problem for the first time. Therefore, large volumes of search work are performed by qualified electricians.

However, anyone who is sufficiently versed in electricity can independently carry out searches and further repairs. A device for finding wires will help him. At its core, it is a detector or device for locating cables that cannot be detected visually. Using this device is not difficult at all, just read the operating instructions carefully.

Operating principle

The operation of devices for searching hidden electrical wiring is based on the following principles:

In the first case, the device will react to the metal structure of the conductor and signal the presence of metal in one of the ways provided for by the detector design (usually a light or sound alarm, but options with liquid crystal displays are possible).

The disadvantage of this type of device is the very low detection accuracy. The result of examining a reinforced concrete panel, for example, can be very distorted due to the fact that the device, along with wires, will also show the presence of reinforcement and mounting loops.

In the second case, a sensor built into the device will determine the presence of a conductor by the propagated magnetic field. The number of “false positives” will be minimal, but for positive search results the wiring must be energized. And some devices will be able to detect a magnetic field only if there is also a fairly high power load in the network.

But what if the wiring is damaged and no current flows through it, for example, when searching for a cable break? For this purpose, there are devices that have the properties of both types. With their help, it is easy to identify the wiring in the wall without the fear of bumping into a reinforcing rod instead.

Overview of detector models

Currently, the most common devices for searching for hidden wiring in walls are several devices from different manufacturers.

Woodpecker

E-121 or “Woodpecker” is an inexpensive device that can, with fairly high accuracy, determine not only the location of hidden wiring at a distance of up to 7 cm from the surface of the walls, but also find the location of a break due to mechanical damage to the wire. Using this tester, you can completely test the wiring in your apartment if an unknown and unexpected malfunction occurs. The country of manufacture of the device is Ukraine.

MS-258A

The MS-258A MEET tester is a budget device made in China. Determines the presence of metal in a structure according to the manufacturer at a distance of up to 18 cm; it also works by the presence of a magnetic field. The result is indicated in two ways - by turning on the indicator lamp and sound signal. The design has a variable resistor that allows you to adjust the sensitivity of the device. The disadvantage of this model is the low result when it is necessary to detect a shielded or foil cable.

BOSCH DMF

The next BOSCH DMF 10 zoom detector is a good device famous brand. Determines, depending on the settings, the presence of metal, wood, plastic hidden in building structures. The device has a multifunctional liquid crystal display, which displays the setup process and displays the results.

Wall Scanner

Model Wall Scanner 80 is a device similar in properties to its predecessor in the review. Produced mainly in China by ADA enterprises. Depending on the settings, it can be used to find various materials in building structures. The device is quite compact and light in weight.

Microphone, radio receiver and thermal imager

In the absence of a device to detect hidden wiring, the search can be carried out in a variety of ways. in various ways. In most cases, detectors are replaced with electrical devices for other purposes.

As a finder, you can successfully use a regular audio microphone connected to an amplifier with a loudspeaker (speaker). As the microphone approaches the intended location of the electrical wiring, it should produce an increasing background sound. And the closer the microphone is to the wiring, the stronger and louder the sound should be. Obviously, this search method works when there is voltage in the hidden wiring. The device will not detect de-energized wiring.

Instead of a microphone, you can use a portable radio with frequency control for searching. Having tuned it to a frequency of about 100 kHz, you need to use smooth movements along the wall to examine the location where the cables are supposed to be located. When the radio receiver approaches a conductor hidden in the wall, the device's speaker should emit an increasing crackling and hissing sound - a consequence of interference created by the electric current.

It is worth paying attention to the possibility of using a device such as a thermal imager to search for hidden wiring and the presence of faults. It will quickly and accurately show not only the presence and location of cables in the walls, but also the locations of breaks or short circuits. Its use is based on the property of a conductor to emit a certain amount of heat when passing an electric current.

De-energized conductors with a break will appear on the screen of a thermal imager as cold, and when shorted, on the contrary, they will glow very brightly.

Application of the scheme

In the case where none of the detectors are at hand, you can determine the location of hidden wiring absolutely without instruments. To do this, it is enough to know that according to established rules, wires and cables are laid strictly vertically or horizontally in the walls. Along the ceilings, wires run in straight lines connecting lighting fixtures to distribution boxes or switches, parallel to the walls of the room and located in the voids of the floors or in pipes behind the structure suspended ceilings. All wire connections are made in junction boxes.

How does this knowledge help in your search? You can draw a diagram of existing hidden wiring or a section of it on walls and ceilings, and then use this diagram in the future without having expensive devices. First you need to draw straight lines vertically upward from sockets and switches. Distribution boxes should be located on the wall, at a height of 150-250 mm from the ceiling.

You can determine their location by tapping the walls. Based on the changed sound, the boxes are marked and connected with straight lines, which will indicate the location of the cables. The connection of boxes and distribution board also occurs along straight vertical or horizontal lines. Of course, all these rules are valid for hidden wiring, and it is recommended to use them only when searching for fault locations due to the very low accuracy of determination. In the case of open wiring, obviously, you can do without the device and tapping.

How to find a cliff

To first, you need to determine the location where the break or short circuit supposedly occurred. The search algorithm is simple.

If there is no voltage in individual sockets or lamps within one group, there is a break in one of the sections of the wire. Here you need to cut off the non-working sockets with a mental line. A distribution box will immediately be detected, after which there is no current in the conductors. All that remains is to check the presence of voltage in this junction box using such a well-known device as an indicator screwdriver or a multimeter. If there is no voltage, you need to look for a break in the area preceding this node on the side of the switchboard.

If there is no voltage in the entire group, and the circuit breaker protecting it is triggered, then with a high degree of probability a short circuit has occurred in one of the electrical wiring sections. It can be diagnosed by measuring the resistance of each section, disconnecting it from the box and removing all the load from it.

To obtain an accurate result, each section must be tested. A short circuit is detected where the resistance is zero. You can use a regular tester for these purposes.

You can search for the location of the short circuit by sequentially disconnecting sections in the boxes, starting from the side of the furthest circuit from the distribution board. After disconnecting each individual section, it is necessary to check the functionality of the circuit by applying voltage until the circuit breaker stops switching off. This search method must be used with great care to protect yourself and other workers from electric shock.

It should be noted that the above methods of searching for hidden wiring become irrelevant if there is a technical passport, which reflects all the information on the location of electrical wiring in the room. If there is no technical certificate, it is strongly recommended that after discovering the wiring and replacing it, draw up a diagram in order to avoid labor-intensive work in the future.

What is the effect of a magnetic field on a current-carrying conductor?

A magnetic field acts with some force on any current-carrying conductor located in this field.

1. How to show that a magnetic field acts on a current-carrying conductor located in this field?

It is necessary to suspend the conductor on flexible wires connected to the current source.
When this conductor with current is placed between the poles of a permanent arc-shaped magnet, it will begin to move.
This proves that a magnetic field acts on a current-carrying conductor.

2. What determines the direction of movement of a conductor carrying current in a magnetic field?

The direction of movement of a conductor carrying current in a magnetic field depends on the direction of the current in the conductor and on the location of the magnet poles.

3. What device can be used to rotate a current-carrying conductor in a magnetic field?

The device, which can be used to rotate a current-carrying conductor in a magnetic field, consists of a rectangular frame mounted on a vertical axis.
A winding consisting of several dozen turns of wire coated with insulation is laid on the frame.
Since the current in the circuit is directed from the positive pole of the source to the negative, in opposite parts of the frame the current has the opposite direction.
Therefore, the magnetic field forces will also act on these sides of the frame in opposite directions.
As a result, the frame will begin to rotate.

4. What device in the frame is used to change the direction of the current every half turn?

The frame with the winding is connected to electrical circuit through half rings and brushes, allowing you to change the direction of current in the winding every half turn:
- one end of the winding is connected to one metal half-ring, the other - to the other;
- half rings rotate in place with the frame;
- each half-ring is pressed against a metal brush plate and slides along it when rotated;
- one brush is always connected to the positive pole of the source, and the other to the negative pole;
- when you turn the frame, the half rings will turn with it and each will press against another brush;
- as a result, the current in the frame will change direction to the opposite;
In this design, the frame rotates in one direction all the time.

5. How does a technical electric motor work?

The rotation of a coil with current in a magnetic field is used in the design of an electric motor.
In electric motors, the winding consists of a large number of turns of wire.
They are placed in slots on the side surface of the iron cylinder.
This cylinder is needed to enhance the magnetic field.
The cylinder with the winding is called the motor armature.
The magnetic field in which the armature of such a motor rotates is created by a strong electromagnet.
The electromagnet and the armature winding are powered by the same current source.
The motor shaft (the axis of the iron cylinder) transmits rotation to the payload.