Solar radiation meter (luxmeter)
To help technical and scientific staff, many measuring instruments have been developed to ensure accuracy, convenience and efficiency. At the same time, for most people, the names of these devices, and even more so the principle of their operation, are often unfamiliar. In this article, we will briefly reveal the purpose of the most common measuring instruments. Information and images of devices were shared with us by the website of one of the suppliers of measuring devices.
Spectrum analyzer- This is a measuring device that serves to observe and measure the relative distribution of energy of electrical (electromagnetic) oscillations in a frequency band.
Anemometer- a device designed to measure the speed, volume of air flow in a room. The anemometer is used for sanitary and hygienic analysis of territories.
Balometer– a measuring device for direct measurement of the air volume flow on large supply and exhaust ventilation grilles.
Voltmeter is a device that measures voltage.
Gas analyzer- a measuring device for determining the qualitative and quantitative composition of gas mixtures. Gas analyzers are either manual or automatic. Examples of gas analyzers: freon leak detector, hydrocarbon fuel leak detector, particulate number analyzer, flue gas analyzer, oxygen meter, hydrogen meter.
Hygrometer is a measuring device that serves to measure and control the humidity of the air.
Rangefinder- a device that measures distance. The rangefinder also allows you to calculate the area and volume of an object.
Dosimeter- a device designed to detect and measure radioactive emissions.
RLC meter- a radio measuring device used to determine the total conductivity of an electrical circuit and impedance parameters. RLC in the name is an abbreviation of the circuit names of elements whose parameters can be measured by this device: R - Resistance, C - Capacitance, L - Inductance.
Power meter- a device that is used to measure the power of electromagnetic oscillations of generators, amplifiers, radio transmitters and other devices operating in the high-frequency, microwave and optical ranges. Types of meters: absorbed power meters and transmitted power meters.
THD meter- a device designed to measure the coefficient of non-linear distortion (coefficient of harmonics) of signals in radio engineering devices.
Calibrator- a special standard measure that is used for verification, calibration or graduation of measuring instruments.
Ohmmeter, or resistance meter is a device used to measure the resistance to electric current in ohms. Varieties of ohmmeters depending on sensitivity: megaohmmeters, gigaohmmeters, teraohmmeters, milliohmmeters, microohmmeters.
Current clamp- a tool that is designed to measure the amount of current flowing in a conductor. Current clamps allow you to measure without breaking the electrical circuit and without disturbing its operation.
thickness gauge- this is a device with which you can, with high accuracy and without violating the integrity of the coating, measure its thickness on a metal surface (for example, a layer of paint or varnish, a layer of rust, a primer, or any other non-metallic coating applied to a metal surface).
Luxmeter- This is a device for measuring the degree of illumination in the visible region of the spectrum. Light meters are digital, highly sensitive devices such as luxmeter, brightness meter, pulse meter, UV radiometer.
pressure gauge- a device that measures the pressure of liquids and gases. Types of pressure gauges: general technical, corrosion-resistant, pressure gauges, electrocontact.
multimeter- This is a portable voltmeter that performs several functions at the same time. The multimeter is designed to measure DC and AC voltage, current, resistance, frequency, temperature, and also allows you to carry out continuity and diode testing.
Oscilloscope- This is a measuring device that allows you to monitor and record, measure the amplitude and time parameters of an electrical signal. Types of oscilloscopes: analog and digital, portable and desktop
Pyrometer is a device for non-contact temperature measurement of an object. The principle of operation of the pyrometer is based on measuring the thermal radiation power of the measurement object in the range of infrared radiation and visible light. The accuracy of temperature measurement at a distance depends on the optical resolution.
Tachometer- This is a device that allows you to measure the speed of rotation and the number of revolutions of rotating mechanisms. Types of tachometers: contact and non-contact.
Thermal imager- This is a device designed to observe heated objects by their own thermal radiation. The thermal imager allows you to convert infrared radiation into electrical signals, which in turn, after amplification and automatic processing, are converted into a visible image of objects.
Thermohygrometer is a measuring device that simultaneously measures temperature and humidity.
Road defect detector- This is a universal measuring device that allows you to determine the location and direction of cable lines and metal pipelines on the ground, as well as determine the location and nature of their damage.
pH meter is a measuring device designed to measure the hydrogen index (pH index).
Frequency meter– a measuring device for determining the frequency of a periodic process or the frequencies of the harmonic components of the signal spectrum.
Sound level meter- a device for measuring sound vibrations.
Table: Units of measurement and designations of some physical quantities.
Noticed an error? Select it and press Ctrl+Enter
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 hang the conductor on flexible wires connected to a current source.
When this conductor with current is placed between the poles of a permanent arcuate 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 current-carrying conductor in a magnetic field?
The direction of movement of a conductor with current in a magnetic field depends on the direction of the current in the conductor and on the location of the poles of the magnet.
3. What device can be used to rotate a current-carrying conductor in a magnetic field?
The device, on which it is possible to carry out the rotation of a conductor with current in a magnetic field, consists of a rectangular frame mounted on a vertical axis.
A winding is laid on the frame, consisting of several tens of turns of wire covered with insulation.
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 forces of the magnetic field will also act on these sides of the frame in opposite directions.
As a result, the frame will begin to rotate.
4. With the help of what device in the frame do they change the direction of the current every half a turn?
The frame with the winding is connected to the electrical circuit through half rings and brushes, which allows you to change the direction of the current in the winding every half a turn:
- one end of the winding is connected to one metal half-ring, the other - to the other;
- half rings rotate in place with a frame;
- each half-ring is pressed against a metal plate-brush and slides along it during rotation;
- one brush is always connected to the positive pole of the source, and the other to the negative;
- when the frame is rotated, the half-rings will turn with it and each will press against the other brush;
- as a result, the current in the frame will change direction to the opposite;
In this design, the frame rotates all the time in one direction.
5. How does a technical electric motor work?
The rotation of a coil with current in a magnetic field is used in the device 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 amplify the magnetic field.
The winding cylinder is called the motor armature.
The magnetic field in which the armature of such an engine 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 the rotation to the payload.
§61. The action of a magnetic field on a current-carrying conductor. Electrical engine
Questions
1. How to show that a magnetic field acts on a current-carrying conductor located in this field?
1. If you hang the conductor on thin flexible wires in the magnetic field of a permanent magnet, then when you turn on the electric current in the network with the conductor, it will deviate, demonstrating the interaction of the magnetic fields of the conductor and the magnet.
2. Using Figure 117, explain what determines the direction of movement of a current-carrying conductor in a magnetic field.
2. The direction of movement of a conductor with current in a magnetic field depends on the direction of the current and on the location of the poles of the magnet.
3. What device can be used to rotate a current-carrying conductor in a magnetic field? What device is used in the loop to change the direction of the current every half a turn?
3. It is possible to carry out the rotation of a current-carrying conductor in a magnetic field using the device shown in fig. 115, in which a frame with an insulated winding is connected to the network through conductive half rings and brushes, which allows you to change the direction of the current in the winding in half a turn. As a result, the frame rotates all the time in one direction.
4. Describe the device of a technical electric motor.
4. A technical electric motor incorporates an anchor - this is an iron cylinder having slots along the side surface into which the winding turns fit. The armature itself rotates in a magnetic field created by a strong electromagnet. The engine shaft, passing along the central axis of the iron cylinder, is connected to the device, which is driven by the engine into rotation.
5. Where are electric motors used? What are their advantages over thermal ones?
5. DC motors are especially widely used in transport (trams, trolleybuses, electric locomotives), in industry (for pumping oil from a well) in everyday life (in electric shavers). Electric motors are smaller in size compared to thermal motors, and also have a much higher efficiency, in addition, they do not emit gases, smoke and steam, i.e., they are more environmentally friendly.
6. Who and when invented the first electric motor suitable for practical use?
6. The first electric motor suitable for practical use was invented by a Russian scientist - Boris Semenovich Jacobi in 1834. Task 11
1. In fig. 117 showing a diagram of an electrical measuring instrument. In it, the frame with the winding in the off state is held by springs in a horizontal position, while the arrow, rigidly connected to the frame, indicates the zero value of the scale. The entire core frame is placed between the poles of a permanent magnet. When the device is connected to the network, the current in the frame interacts with the magnet field, the frame with the winding turns and the arrow turns on the scale, and in different directions, depending on the direction of the current, and the angle depends on the magnitude of the current.
2. In fig. 118 shows an automatic device for turning on the bell if the temperature exceeds the allowable one. It consists of two networks. The first contains a special mercury thermometer, which serves to close this circuit when the mercury in the thermometer rises above a predetermined value, a power source, an electromagnet, the armature of which closes the second circuit, which contains, in addition to the armature, a bell and a power source. You can use such an automatic machine in greenhouses, incubators, where it is very important to monitor the maintenance of the desired temperature.
Devices whose main purpose is to measure the dose rate of radiation (alpha, beta and gamma, taking into account X-ray) and thereby check for the radioactivity of suspicious objects.
Dosimetric devices are used to determine the levels of radiation on the ground, the degree of contamination of clothing, human skin, food, water, fodder, transport and other various items and objects, as well as to measure the doses of radioactive exposure of people when they are at objects and areas contaminated radioactive substances.
They are used for chemical analysis of air, which provides information on the qualitative and quantitative composition of pollutants and allows predicting the degree of pollution. The main internal pollutants include interior items, furniture, floor and ceiling coverings, building and finishing materials. Chemical analysis of air reveals indicators such as dust, sulfur dioxide, nitrogen dioxide, carbon monoxide, phenol, ammonia, hydrogen chloride, formaldehyde, benzene, toluene, etc.
Instruments for measuring the hydrogen index (pH index). Investigate the activity of hydrogen ions in solutions, water, food products and raw materials, environmental objects and production systems, including in aggressive environments.
Serve to assess the quality of drinking water. Show the amount of inorganic impurities suspended in water, mainly salts of various metals. In everyday life, they are used to determine the quality of tap water, bottled water, as well as to control the effectiveness of water treatment filters.
Portable instruments designed to measure the exact sound level. Noise is called an environmental pollutant. It is also harmful like tobacco smoke, like exhaust gases, like radiation activity. Noise can have a total of four types of source. Therefore, it is customary to divide it into: mechanical, hydromechanical, aerodynamic and electromagnetic. Modern devices are able to determine the noise level of any mechanisms: land, water and even power lines. The device will allow you to objectively measure the sound volume level.
Portable devices designed to measure the exact level of illumination produced by various light sources. The scope of luxmeters is wide, which is explained, first of all, by their high spectral sensitivity, which approaches the sensitivity of the human eye. It should be remembered that some sources of lighting devices, halogen, fluorescent and even LED lamps, after some time of operation lose a significant amount of light flux, the overall illumination in the room may deteriorate. This will not only reduce the visual acuity of a person, but will also affect his fatigue. Illumination should be constantly monitored.
Devices designed for express determination of the amount of nitrates in vegetables, fruits, meat and other food products. Not so long ago, to conduct such studies, an entire laboratory was required, now it can be done using one compact device.
Portable nitrate meters have gained wide popularity due to their compactness, low cost and ease of use. Nitrates are present in many fertilizers that are actively used in agriculture to increase crop yields. For this reason, nitrates in vegetables and fruits are often found in significant concentrations. Getting into the human body with food, nitrates in large quantities can cause nitrate poisoning, various disorders and chronic diseases.
The nitrate indicator will help you recognize dangerous products in time and protect yourself from nitrate poisoning.
For waves of 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 a 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. The satellites used for radio communication are launched into a geostationary orbit, the period of revolution in 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 hovering 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 the Earth and then relays it back. Satellite TV has already become quite common, in any city you can see "dishes" - antennas for receiving satellite signals. However, in addition to television signals, a lot of other signals are transmitted via satellites, in particular, Internet signals, 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 the propagation of radio waves are illustrated in Fig.3.
All radio waves are divided into several ranges depending on their length. The names of the ranges, the properties of the propagation of radio waves and the characteristic areas of use of the waves are given in the table.
Radio wave bands |
|||
Wave range | Wavelengths | Propagation Properties | Usage |
They go around the surface of the Earth and obstacles (mountains, buildings) | Broadcasting |
||
Broadcasting, radio communication |
|||
Short | Rectilinear propagation, reflected from the ionosphere. |
||
Ultrashort | 1 - 10 m (meter) | Rectilinear propagation, passing through the ionosphere. | Broadcasting, television broadcasting, radio communication, radar. |
1 - 10 dm (decimeter) |
|||
1 - 10 cm (centimeter) |
|||
1 - 10 mm (millimeter) |
The generation of radio waves occurs as a result of the movement of charged particles with acceleration. A wave of a given frequency is generated by the oscillatory motion of charged particles with this frequency. When a radio wave acts on free charged particles, an alternating current of the same frequency as the frequency of the wave arises. This current can be registered by the 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. * Express a hypothesis, what can 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. The 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 opportunities does radar provide?
Radio communication. Radar. wave modulation.
0 "style="border-collapse:collapse;border:none">
Alexander Stepanovich Popov (1859 - 1906) - famous Russian physicist, inventor of the radio. Carried out the first experiments on the practical application of 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 somehow changed or, in scientific terms, modulate(from lat. modulatio - dimension, dimension). Protozoa radio wave modulation was used in the first radiotelegraphs, for which Morse code was used. Using the key, the radio transmitters were turned on for a longer or shorter time. Long intervals corresponded to the dash sign, and short intervals 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 gap. On Fig. Figure 1 shows a graph of the oscillations of a wave that transmits a dash-dot-dot-dash signal. (Note that in a real signal, a much larger number of oscillations fit into one dot or dash).
Naturally, it was impossible to transmit voice or music with such a signal, so later they began to use a different modulation. As you know, sound is a pressure wave. For example, a pure sound corresponding to a note of the first octave corresponds to a wave whose pressure varies according to a sinusoidal law with a frequency of 440 Hz. With the help of a device - a microphone (from the Greek micros - small, phone - sound), pressure fluctuations can be converted into an electrical signal, which is a voltage change with the same frequency. These oscillations can be superimposed on the oscillation of a radio wave. One such modulation method is shown in Fig. 2. Electrical signals corresponding to speech, music, and images have a more complex form, but the essence of the modulation remains unchanged - the envelope of the radio wave amplitude 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 that carries image information.
At present, there is a tendency to return to the original "dots" and "dashes". The fact is that any sound and video information can be encoded as a sequence of numbers. It is this 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 encoded with a certain 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, two digits 0 and 1 are used. Obviously, these numbers are similar to the dots and dashes of Morse code. Digitally encoded signals 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 TVs to some program, some used mobile phones. Our ether is filled with a wide variety of radio signals, and their number is constantly increasing. Isn't it "cramped" for them there? Are there any restrictions on the number of simultaneously operating radio and TV transmitters?
It turns out that there is a limit 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 the wave a in Fig. 2 has a frequency w, lying in the range of radio waves, 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 in is actually three radio waves with frequencies w-W, w and w+W. The more information a wave contains, the greater the range of frequencies 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 affect each other, that is, so that the transmitted information is not distorted, the bands occupied by radio stations should not overlap. This imposes a limit on the number of radio transmitters operating on each band.
With the help of radio waves, it is possible to transmit various information (sound, image, computer information), for which it is necessary to modulate the waves. The modulated wave occupies a certain frequency band. In order for the waves of different transmitters not to interfere, their frequencies must differ by a value greater than the frequency band.
Principles of radar.
Another important application of radio waves is radar, based on the ability of radio waves to reflect off various objects. Radar allows you to determine the location of an object and its speed. For radar, decimeter and centimeter waves are used. The reason for this choice is very simple, longer waves, due to the phenomenon of diffraction, go around objects (aircraft, ships, cars), practically without being reflected from them. In principle, the tasks of radar can also be solved with the help of electromagnetic waves in the visible range of the spectrum, that is, by visual observation of an object. However, visible radiation is delayed by such components of the atmosphere as clouds, fog, dust, smoke. For radio waves, these objects are completely transparent, which allows the use of radar in all weather conditions.
To determine the location, you must 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 the 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 the object, narrowly directed antennas are used. Such antennas form a wave in the form of a narrow beam, so that the object enters this beam only at a certain location of the antenna (the action is similar to the beam of a flashlight). In the process of radar, the antenna "turns" so that the wave beam scans a large area of space. The word "rotates" is in quotation marks because no mechanical rotation occurs in modern antennas, the antenna's directivity is changed electronically. The principle of radar is illustrated in Fig. 3.
Radar makes it possible to set the distance to the object, the direction to the object and the speed of the object. Due to the ability of radio waves to freely pass through clouds and fog, radar techniques can be used in all weather conditions.
1. ○ What is the length of the radio waves used for communication?
2. ○ How to “force” a radio wave to carry information?
3. ○ What is the limit on the number of radio stations on the air?
4. Assuming that the transmission frequency must be 10 times the bandwidth occupied by the signal, calculate the minimum wavelength for transmitting a television signal.
5. * How can radar determine the speed of an object?
Section 27.Principles of operation of mobile telephony.
(Practical lesson)
If Edison had such conversations, the world would not see either a gramophone or a telephone.
I. Ilf, E. Petrov
How does mobile phone work? What elements are included in the composition of a mobile telephone and what is their functional purpose? What are the prospects for the development of mobile telephony?
0 "style="border-collapse:collapse;border:none">
Lifestyle.
1. When using a mobile phone, there is a constant emission of radio waves in the immediate vicinity of the brain. Currently, scientists have not come to a consensus on the degree of influence of such radiation on the body. However, you should not conduct excessively long conversations on a 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 the flight or at certain times of the flight (takeoff, landing). If such prohibitions exist, observe them, it is in your interest!
3. Some parts of the mobile device, such as the LCD display, may be damaged when exposed to strong sunlight or high temperatures. Other elements, such as electronic circuitry that converts signals, may deteriorate when exposed to moisture. Protect your mobile phone from such harmful influences!
Answer to task 1.
Compared to conventional telephony, mobile telephony 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 the mobile handset does not need to be powerful, and therefore can be small and light.
Answer to task 2. For mobile communications, ultrashort waves should be used.
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 are spread over a line-of-sight distance, it is necessary to have a network of relay stations. To communicate with other telephone stations located in distant regions, it is necessary to have access to the intercity and international network.
Answer to task 5. The apparatus must contain information input and output devices, a device that converts an information signal into a radio wave and back a radio wave into an information signal.
Answer to task 6. First of all, using the telephone, we transmit and perceive sound information. However, the apparatus can also give us visual information. Examples: the phone number on which we are called, the phone number of our friend, which we entered into the memory of our phone. Modern devices are able to perceive 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 the buttons on which numbers and letters are indicated.
Answer to task 7. Entering audio information - microphone, sound information output – telephone, input of video information video camera, video information output – display, as well as buttons for entering information in the form of letters and numbers.
Answer to task 8.
(The dotted box in the illustration means that this device is not necessarily part of a mobile phone).
§28. Geometric optics and optical devices.
(Lesson-lecture).
Then, sparing no labor or expense, I succeeded in making an instrument so perfect that when looked through it, objects appeared almost a thousand times larger and more than thirty times closer than those naturally seen.
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 a visual increase? 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 devices . (Physics 7-9 cells). Natural Science 10, § 16.
Geometric optics and lens properties.
Light, like radio waves, is an electromagnetic wave. However, the wavelength of visible radiation is a few tenths of a micrometer. Therefore, such wave phenomena as interference and diffraction practically do not manifest themselves under normal conditions. This, in particular, led to the fact that the wave nature of light was not known for a long time, and even Newton assumed that light is a stream of particles. It was assumed that these particles move from one object to another in a straight line, and the streams of these particles form rays that can be observed by passing light through a small hole. This consideration 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 different transparent substances. As a result, the properties of the 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's recall how an image is built in a thin converging lens (see Fig. 1).
The object is represented as a set of luminous dots, and its image is built by dots. To draw a point image A you need to use two beams. One beam goes parallel to the optical axis, and after refraction in the lens passes through the focus F'. The other beam passes without being refracted through the center of the lens. The point at the intersection of these two rays A' and will be the image of the point A. Remaining point arrows ending at a dot A are constructed in a similar way, resulting in an arrow ending at a point A'. Note that the 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 focus of the lens to the lens. The image of an object can be either reduced or enlarged. The coefficient of increase (decrease) is easy to obtain, based on Fig. 1 and similarity properties of triangles: G = d¢ /d. The following property can be deduced from the last two formulas: the image is reduced if d>2f(in this case f< d¢ < 2f). It follows from the reversibility of the path of the rays 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 large 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 focus from the lens.
Lenses in various devices.
The described property of lenses is used in various devices where converging lenses are used as lenses. Strictly speaking, any quality lens consists of a lens system, but its effect is the same as that of a single converging lens.
Devices that enlarge the image are called projectors. Projectors are used, for example, in cinemas, where an image on a film with a size of a few centimeters is enlarged to a screen size of several meters. Another type of projectors are multimedia projectors. In them, the signal coming from a computer, video recorder, image recording device on video disks forms a small image, which is projected through the lens onto a large screen.
Much more often you need to reduce rather than enlarge the image. This is what lenses are used for in cameras and camcorders. An image of several meters, for example, the image of a person, is reduced to a size of a few centimeters or a few millimeters. The receiver where the image is projected is a photographic film or a special matrix of semiconductor sensors ( CCD) that converts the video image into an electrical signal.
Image reduction is used in the production of microcircuits used in electronic devices, in particular in computers. Elements of microcircuits - semiconductor devices, connecting wires, etc. have dimensions of several micrometers, and their number on a silicon plate with dimensions of the order of a centimeter reaches several million. Naturally, it is impossible to draw so many elements of this scale without zooming in with a lens.
Zoom lenses are used in telescopes. Objects such as galaxies, which are millions of light years in size, "fit" on a film or CCD array with dimensions of a few centimeters.
Concave mirrors are also used as lenses in telescopes. The properties of a concave mirror are in many respects similar to those 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 that 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 an object approaches and decreasing it when moving away. The ability to change focal length is called accommodation. The normal eye is able to focus the image 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 action of which is equivalent to a decrease in the focal length of the lens. Correction of the opposite defect of vision - myopia occurs with the help of a diverging lens.
Devices that give visual magnification.
With the help of the eye, we can only estimate the angular dimensions of an object (see § 16 Natural History 10). For example, we can close the image of the Moon with a pinhead, that is, the angular dimensions of the Moon and the pinhead can be made the same. You can achieve visual magnification either by bringing the object closer to the eye, or by somehow magnifying it at the same distance from the eye (Fig. 4).
Trying to consider some small object, we bring it closer to the eye. However, with a very strong approximation, our lens does not cope with the work, the focal length cannot decrease so that we can view the object, for example, from a distance of 5 cm. You can correct the situation 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 a normal eye can comfortably see a small object is called the distance of best vision. Usually this distance is taken equal to 25 cm. If a magnifying glass allows you to view an object, for example, from a distance of 5 cm, then a visual increase of 25/5=5 times is achieved.
And how to get a visual increase, for example, of the Moon? With the help of 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 how the Kepler tube works (see § 16 Natural History 10).
Visual magnification, 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 how a microscope works.
Lenses and lens systems are used in many devices. Instrument lenses allow you to get both enlarged and reduced images of the object. Visual magnification is achieved by increasing the angular size of the object. For this, a magnifying glass or an eyepiece in a system with a lens is used.
1. On what property of rays is the action of lenses based?
2. * Based on the method of constructing an image in a converging lens, explain why the focal length of the lens should change when the distance between the object and the eye changes?
3. In a microscope and a Kepler tube, the image is inverted. Which lens, lens or eyepiece inverts the image?
§ 29. The principle of operation of points.
(Lesson-workshop).
The monkey has become weak with eyes in old age,
But she heard from people
That this evil is not of such a big hand,
You just need to get glasses.
What happens during eye accommodation? What is the difference between normal, nearsighted and farsighted eyes? How does the action of the lens correct visual impairment?
Lens. Focal length of the lens. The eye as an optical system. Optical devices . (Physics grades 7-9). Visual disturbances. (Biology, basic school).
Objective: Using a multimedia program to study the work of the lens of the eye in normal, nearsighted and farsighted vision. Explore how a lens corrects visual impairment.
Equipment: Personal computer, multimedia disk ("Open Physics").
Work plan: Performing the task in sequence, explore the possibilities of accommodation of a normal, nearsighted and farsighted eye. Investigate the accommodation of the nearsighted and farsighted eyes in the presence of a lens in front of the eye. Choose a lens for the appropriate eye.
You already know that such visual defects as nearsightedness and farsightedness are associated with the inability to give the lens of the eye an optimal curvature through the work of the eye muscles. With myopia, the lens remains too convex, its curvature is excessive, and, accordingly, the focal length is too short. The reverse takes place in farsightedness.
Recall that instead of the focal length, another physical quantity can be used to characterize the lens - optical power. Optical power is measured in diopters and is defined as the reciprocal of the focal length: D = 1/f(1 diopter = 1/1m). The optical power of a diverging lens has a negative value. The optical power of the lens is always positive. However, for a near-sighted eye, the optical power of the lens is too large, and for a far-sighted 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 standing lenses are added (taking into account the sign).
Exercise 1. Examine the functioning of a normal eye without a lens. You are offered three options for accommodation: normal - for the distance of the best vision, far - for an infinite 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 in this case is the image focused inside the eye? What is the distance of best vision in this program?
Task 2. Explore the effect of a magnifying glass. Set the normal eye to normal accommodation. Place a converging lens in front of the eye with the highest possible optical power. Find the distance at which the eye is focused. Using the material of the previous paragraph, determine how many times this magnifying glass magnifies?
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 the automatic accommodation of the eye. Adjust the lens so that the eye is focused as the distance changes from the best vision distance (25 cm) to the infinite distance. What are the limits of the optical powers of the lenses, in which glasses for the "eyes" given in the program can successfully perform their functions.
Task 5. Try to achieve optimal results for nearsightedness and farsightedness, when the selected lens will focus the eye at distances from infinite to the smallest 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 blurred. To correct, glasses with divergent lenses are required. Rays from nearby objects, after passing through the lens of a far-sighted eye, are focused behind the retina, and the image becomes blurred. Corrective glasses with converging lenses are required.
§ 25. Electricity and ecology.
(Lesson-conference).
It occurred to me more than once that work in hydraulic engineering construction is the same war. In war you don’t have to yawn, otherwise you will be knocked over, and here you have to work continuously - 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 principle of operation of a hydroelectric power plant (HPP)? What impact on the ecological situation can the construction of thermal power plants and hydroelectric power plants have?
The 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 plants. Understand the impact on the environment that the construction of these types of power plants can have.
Conference plan:
1. Design and operation of a modern thermal power plant.
2. Design 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 a rapid breakthrough in the field of electric power industry that made it possible to turn an agrarian power into an industrialized country in the shortest possible time. 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 came, at the cost of what human resources, at the cost of what changes in nature. Any medal always has two sides, and an educated person must see and compare both sides.
Message 1. Factory of electricity and heat.
The combined heat and power plant is one of the most common electricity producers. The main mechanism of CHP is a steam turbine that drives a generator of electricity. The most expedient is the construction of thermal power plants in large cities, since the steam exhausted in the turbine enters the heating system of the city and supplies heat to our homes. The same steam heats the hot water that enters our homes.
Message 2. How a hydroelectric power plant works.
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 nothing”. However, hydroelectric power plants are very expensive hydraulic structures. The cost of building a hydroelectric power station is different. The most quickly paid off are 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 rather large territories from industrial and agricultural circulation.
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 the negative consequences is one of the tasks that arise in the design of power plants. But, first of all, it is necessary to be aware of the negative impact on the nature of powerful installations for the production of electricity.
Burning a large amount of 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 burns, should not have a negative impact on nature. However, the construction of lowland HPPs is always associated with the flooding of vast territories. Many of the environmental consequences of such flooding, produced in the middle of the 20th century, are only now beginning to show. Blocking the rivers with dams, we inevitably invade the life of the inhabitants of the reservoirs, which also has negative consequences. There is, for example, an opinion that all the electricity generated by the Volga HPPs is not worth the losses associated with a decrease in the sturgeon catch.
Information sources.
1. Children's encyclopedia.
2. Kirillin of the history of science and technology. - M.: Science. 1994.
3. Vodopyanov consequences of NPT. Minsk: Science and technology, 1980.
5. Non-traditional sources of energy. - M: Knowledge, 1982.
6., Skalkin aspects of environmental protection .- L .: Gidrometeoizdat, 1982.
7. Nikitin - technical progress, nature and man.-M: Science 1977.
8., Spielrain. Problems and prospects. - M: Energy, 1981.
9. Physics and scientific and technological progress / Ed. , .- M: Enlightenment, 19888
10. Energy and environmental protection / Ed. etc.-M.: Energy, 1979.
Modern power plants are complex engineering structures. They are necessary for the existence of modern society. However, their construction should be carried out in such a way as to minimize the damage to nature.
