Light is simply necessary for every person to have a great mood and mental health. Thanks to it, we get the opportunity to see objects, distinguish their shape and the structure of materials, because the artificial extension of daylight hours allows us to increase efficiency and productivity. When choosing fixtures and lamps for yourself, do not forget that the light must be selected correctly. In rooms for different purposes, a variable approach to lighting intensity is acceptable. And in order to choose the right lamps, you need to know how light is measured.
and artificial
All human health experts unanimously declare that the best source of light for people is a natural light source. It promotes the production of a number of vitamins and microelements in the body, and is also most beneficial for the eyes. Every object can be seen in natural light without distortion or glare.
But, unfortunately, the modern world dictates its own conditions, and we can no longer do without artificial light sources in the dark, otherwise the life of cities would come to a complete stop. Each apartment contains a lot of different lamps; quite often we have no idea how light is measured and what we need to pay attention to in the store when buying a variety of sconces, floor lamps and lampshades.
What kind of light is there?
No less important than the selection of light intensity is the category or type of lighting. As we have already said, the most pleasant and safe light is a natural source of lighting. It has a warm tint and is least harmful to the eyes. The closest thing to a similar tone were old incandescent lamps with a reddish tint of light output. They did not irritate the eyes and copied the sunlight entering the apartment windows.
Modern lamps have many variations in the working element and type of light. Before purchasing a new lamp, be sure to check what type of light is indicated on the packaging. For example, warm light would be ideal for living spaces. And neutral is usually used in offices and large industrial premises. Cold light is often used in watchmaking workshops, where its bluish tint helps to distinguish fine details. Cold shades of light are also welcome in subtropical countries, where they create a feeling of additional coolness and transparency of the air.
Based on the above, you can always choose the right type of light bulb that will create the desired mood and level of comfort in a relaxing home atmosphere. Psychologists have proven that the type of light plays a serious role in shaping the working mood in enterprises. Naturally, labor productivity also depends on this.
What parameters are used to measure light intensity?
The average buyer doesn’t even think about how light is measured and how important this information is. After all, light, being measured, is measured according to many quantitative and qualitative parameters. They must be taken into account when planning renovations in the apartment and counting the number of light bulbs needed for each room.
Light can be measured according to the following characteristics:
- intensity;
- strength;
- brightness
You won’t be able to determine all the necessary parameters just by eye, so you should take care of purchasing devices that will help you maintain your vision and a positive psychological attitude at any time of the day.
How is the brightness of light measured?
Brightness is a very important characteristic of a light source. It is the brightness of the lighting that allows us to see all the objects around us clearly and in contrast. Brightness enhances spatial perception and exposure of whites and blacks. In addition, it is the brightness of the light source that determines the degree of comfort when reading printed text, and this, as is known, directly affects eye health.
If we are talking about brightness, then remembering in what units light is measured is very easy. The candela is most often used to measure the brightness of a light source. This unit denotes the brightness of one candle, and it is from this unit that all measuring instruments are based. Sometimes experts also use other units of measurement - lambert and apostilbe.
What device can measure the brightness of lighting?
Modern specialized equipment stores are always ready to provide customers with a large variety of instruments for measuring light brightness. Brightness meters and colorimeters do the job best. They are able to give you information not only on the degree of brightness in a particular room, but also determine the color temperature of the room.
Devices with advanced functionality are suitable for professional photographers involved in studio shooting. And for household needs, a regular brightness meter that does not have additional options is suitable.
In what
Light power - According to the school physics course, it can be characterized as the energy of light that can be transferred from one point to another in a certain period of time. This energy can change direction depending on the given trajectory.
Light energy is measured in candelas. That is, having bought a brightness meter for home use, you can always measure not only the brightness, but also the intensity of the light.
Light intensity: what is it measured in?
Light intensity is often called illuminance, and it is also important when choosing lamps and different types of lamps. Even a child can remember how light intensity is measured, although some nuances should be taken into account here.
If we are talking about falling on a certain surface, then it is necessary to measure in lumens. But if you want to find out the degree of illumination of objects or surfaces, you need to talk about lux.
Such subtleties often frighten buyers who have heard somewhere that light is measured in lumens, and are perplexed by the incomprehensible units of measurement indicated on the packaging of the light bulb. A very common device - a lux meter - will help you cope with the problem of determining the degree of illumination in a room.
Luxometer - a device that preserves healthy vision
If you have difficulty remembering in what units light is measured, then a lux meter will save your time and nerve cells. This device is small in size and weight, most often it consists of a display and a measuring part.
You can use such an assistant at home, in educational institutions or office premises. To obtain data, you just need to turn on the light source and take measurements. Within a few seconds you will see the result on the display, which will show how safe your light bulbs and lamps are for the eyes.
for apartments and other residential premises
In order to choose lighting that is comfortable for the eyes, it is not enough to know how light is measured. You also need to have information about lighting standards, which you should use when planning the location of lighting fixtures in the apartment.
Each room and space has its own required level of illumination, which is measured in lux. For example, the children's room should be the most illuminated room in the apartment. There cannot be less than two hundred suites here, otherwise the baby’s health will be at great risk.
The kitchen and other rooms can be illuminated with one hundred and fifty lux, but utility rooms and corridors can get by with fifty lux. Compliance with these standards guarantees your family a comfortable existence, excellent mood and vision that even an eagle will envy.
If you care about your family, you should know exactly what light bulbs are installed in the lamps in your apartment. After all, every sane person dreams of returning from work to a home where cheerful children and a caring wife in a good mood are waiting for him. And an important role in making the dream finally become a reality is played by well-chosen lighting.
Radiation (or ionizing radiation) is a collection of different types of physical fields and microparticles that have the ability to ionize substances.
Radiation is divided into several types and measured using various scientific instruments specially designed for this purpose.
In addition, there are units of measurement, exceeding which can be fatal to humans.
The most accurate and reliable ways to measure radiation
Using a dosimeter (radiometer), you can measure the intensity of radiation as accurately as possible and examine a specific place or specific objects. Most often, devices for measuring radiation levels are used in places:
- Close to areas of radiation radiation (for example, near the Chernobyl nuclear power plant).
- Planned residential construction.
- In unexplored, unexplored areas during hikes and travels.
- When potentially purchasing residential properties.
Since it is impossible to clear the territory and objects located on it from radiation (plants, furniture, equipment, structures), the only sure way to protect yourself is to check the level of danger in time and, if possible, stay as far away from sources and contaminated areas. Therefore, under normal conditions, household dosimeters can be used to check the area, products, and household items, which successfully detect the danger and its doses.
Radiation regulation
The purpose of radiation control is not just to measure its level, but also to determine whether the indicators comply with established standards. Criteria and standards for safe levels of radiation are prescribed in separate laws and generally established rules. The conditions for containing man-made and radioactive substances are regulated for the following categories:
- Food
- Air
- Building materials
- Computer equipment
- Medical equipment.
Manufacturers of many types of food or industrial products are required by law to prescribe radiation safety compliance criteria and indicators in their conditions and certification documents. The relevant government services quite strictly monitor various deviations or violations in this regard.
Radiation units
It has long been proven that background radiation is present almost everywhere, it’s just that in most places its level is considered safe. The level of radiation is measured in certain indicators, among which the main ones are doses - units of energy absorbed by a substance at the moment of passage of ionizing radiation through it.
The main types of doses and their units of measurement can be listed in the following definitions:
- Exposure dose– created by gamma or x-ray radiation and shows the degree of ionization of air; non-systemic units of measurement – rem or “roentgen”, in the international SI system it is classified as “coulomb per kg”;
- Absorbed dose– unit of measurement – gray;
- Effective dose– determined individually for each organ;
- Dose equivalent– depending on the type of radiation, calculated based on coefficients.
Radiation radiation can only be determined by instruments. At the same time, there are certain doses and established standards, among which permissible indicators, negative doses of effects on the human body and lethal doses are strictly specified.
Radiation Safety Levels
For the population, certain levels of safe values of absorbed radiation doses have been established, which are measured by a dosimeter.
Each territory has its own natural background radiation, but a value equal to approximately 0.5 microsieverts (µSv) per hour (up to 50 microroentgens per hour) is considered safe for the population. Under normal background radiation, the safest level of external irradiation of the human body is considered to be up to 0.2 (µSv) microsievert per hour (a value equal to 20 microroentgens per hour).
Most upper limit permissible radiation level – 0.5 µSv - or 50 µR/h.
Accordingly, a person can tolerate radiation with a power of 10 μS/h (microsievert), and by reducing the exposure time to a minimum, radiation of several millisieverts per hour is harmless. This is the effect of fluorography and x-rays – up to 3 mSv. A photograph of a diseased tooth at the dentist – 0.2 mSv. The absorbed radiation dose has the ability to accumulate throughout life, but the amount should not cross the threshold of 100-700 mSv.
How is strength measured? In what units is force measured?
- What is the strength in, brother?
- In newtons, brother...
(They stopped teaching physics at school?)
Back in school, we learned that the concept of force was introduced into physics by a man who had an apple fall on his head. By the way, it fell due to gravity. Newton, I think, was his last name. This is what he called the unit of measurement of force. Although he could have called him an apple, it still hit him on the head!
According to the International System of Units (SI), force is measured in newtons.
According to the Technical System of Units, force is measured in ton-force, kilogram-force, gram-force, etc.
According to the GHS System of Units, the unit of force is the dyne.
For some time in the USSR, a unit of measurement called the wall was used to measure force.
In addition, in physics there are so-called natural units, according to which force is measured in Planck forces.
Force is one of the most widely known concepts in physics. Under by force is understood as a quantity that represents a measure of the impact on a body from other bodies and various physical processes.
With the help of force, not only the movement of objects in space can occur, but also their deformation.
The action of any forces on a body obeys Newton's 3 laws.
Unit of measurement force in the international system of units C is Newton. It is denoted by the letter N.
1N represents a force, when exposed to a physical body weighing 1 kg, this body acquires an acceleration equal to 1 ms.
To measure force, use a device such as dynamometer.
It is also worth noting that a number of physical quantities are measured in other units.
For example:
Current strength is measured in Amperes.
Luminous intensity is measured in Candelas.
In honor of the outstanding scientist and physicist Isaac Newton, who did a lot of research into the nature of the existence of processes that affect the speed of a body. Therefore, in physics it is customary to measure force in newtons(1 N).
In physics, the concept of force is measured in newtons. They gave the name Newtons, in honor of the famous and outstanding physicist named Isaac Newton. In physics there are 3 Newton's laws. The unit of force is also called newton.
Force is measured in newtons. The unit of force is 1 Newton (1 N). The very name of the unit of measurement of force comes from the name of a famous scientist named Isaac Newton. He created 3 laws of classical mechanics, which are called Newton's 1st, 2nd and 3rd laws. In the SI system, the unit of force is called Newton (N), and in Latin force is denoted newton (N). Previously, when there was no SI system yet, the unit of force was called the dyne, which was derived from the carrier of one device for measuring force, which was called a dynamometer.
Force in International Units (SI) is measured in Newtons (N). According to Newton's second law, force is equal to the product of a body's mass and its acceleration, respectively Newton (N) = KG x M / S 2. (KILOGRAM MULTIPLIED BY METER, DIVIDED BY SECOND SQUARE).
In principle, one can imagine any large number of different systems of units, but only a few are widely used. All over the world, the metric system is used for scientific and technical measurements and in most countries in industry and everyday life.
Basic units. In the system of units, for each measured physical quantity there must be a corresponding unit of measurement. Thus, a separate unit of measurement is needed for length, area, volume, speed, etc., and each such unit can be determined by choosing one or another standard. But the system of units turns out to be much more convenient if in it only a few units are selected as basic ones, and the rest are determined through the basic ones. So, if the unit of length is a meter, the standard of which is stored in the State Metrological Service, then the unit of area can be considered a square meter, the unit of volume is a cubic meter, the unit of speed is a meter per second, etc.
The convenience of such a system of units (especially for scientists and engineers, who deal with measurements much more often than other people) is that the mathematical relationships between the basic and derived units of the system turn out to be simpler. In this case, a unit of speed is a unit of distance (length) per unit of time, a unit of acceleration is a unit of change in speed per unit of time, a unit of force is a unit of acceleration per unit of mass, etc. In mathematical notation it looks like this:v = l / t , a = v / t , F = ma = ml / t 2 . The presented formulas show the “dimension” of the quantities under consideration, establishing relationships between units. (Similar formulas allow you to determine units for quantities such as pressure or electric current.) Such relationships are of a general nature and are valid regardless of what units (meter, foot or arshin) the length is measured in and what units are chosen for other quantities.
In technology, the basic unit of measurement of mechanical quantities is usually taken not as a unit of mass, but as a unit of force. Thus, if in the system most commonly used in physical research, a metal cylinder is taken as a standard of mass, then in a technical system it is considered as a standard of force that balances the force of gravity acting on it. But since the force of gravity is not the same at different points on the Earth's surface, location specification is necessary to accurately implement the standard. Historically, the location was sea level at latitude 45° . Currently, such a standard is defined as the force necessary to give the specified cylinder a certain acceleration. True, in technology, measurements are usually not carried out with such high accuracy that it is necessary to take care of variations in gravity (if we are not talking about the calibration of measuring instruments).
There is a lot of confusion surrounding the concepts of mass, force and weight.The fact is that there are units of all these three quantities that have the same names. Mass is an inertial characteristic of a body, showing how difficult it is to remove it from a state of rest or uniform and linear motion by an external force. A unit of force is a force that, acting on a unit of mass, changes its speed by one unit of speed per unit of time. All bodies attract each other. Thus, any body near the Earth is attracted to it. In other words, the Earth creates the force of gravity acting on the body. This force is called its weight. The force of weight, as stated above, is not the same at different points on the surface of the Earth and at different altitudes above sea level due to differences in gravitational attraction and in the manifestation of the Earth's rotation. However, the total mass of a given amount of substance is unchanged; it is the same both in interstellar space and at any point on Earth. Precise experiments have shown that the force of gravity acting on different bodies (i.e. their weight) is proportional to their mass. Consequently, masses can be compared on scales, and masses that turn out to be the same in one place will be the same in any other place (if the comparison is carried out in a vacuum to exclude the influence of displaced air). If a certain body is weighed on a spring scale, balancing the force of gravity with the force of an extended spring, then the results of measuring the weight will depend on the place where the measurements are taken. Therefore, spring scales must be adjusted at each new location so that they correctly indicate the mass. The simplicity of the weighing procedure itself was the reason that the force of gravity acting on the standard mass was adopted as an independent unit of measurement in technology.
Metric system of units. The metric system is the general name for the international decimal system of units, the basic units of which are the meter and the kilogram. Although there are some differences in details, the elements of the system are the same throughout the world.
Story. The metric system grew out of regulations adopted by the French National Assembly in 1791 and 1795 defining the meter as one ten-millionth of the portion of the earth's meridian from the North Pole to the equator. By decree issued on July 4, 1837, the metric system was declared mandatory for use in all commercial transactions in France. It gradually replaced local and national systems in other European countries and was legally accepted as acceptable in the UK and USA. An agreement signed on May 20, 1875 by seventeen countries created an international organization designed to preserve and improve the metric system. It is clear that by defining the meter as a ten-millionth part of a quarter of the earth's meridian, the creators of the metric system sought to achieve invariance and accurate reproducibility of the system. They took the gram as a unit of mass, defining it as the mass of one millionth of a cubic meter of water at its maximum density. Since it would not be very convenient to carry out geodetic measurements of a quarter of the earth's meridian with each sale of a meter of cloth or to balance a basket of potatoes at the market with the appropriate amount of water, metal standards were created that reproduced these ideal definitions with extreme accuracy. It soon became clear that metal length standards could be compared with each other, introducing much less error than when comparing any such standard with a quarter of the earth's meridian. In addition, it became clear that the accuracy of comparing metal mass standards with each other is much higher than the accuracy of comparing any such standard with the mass of the corresponding volume of water. In this regard, the International Commission on the Meter in 1872 decided to accept the “archival” meter stored in Paris “as it is” as the standard of length. Similarly, the members of the Commission accepted the archival platinum-iridium kilogram as the standard of mass, “considering that the simple relationship established by the creators of the metric system between the unit of weight and the unit of volume is represented by the existing kilogram with an accuracy sufficient for ordinary applications in industry and commerce, and the exact Sciences do not need a simple numerical relationship of this kind, but an extremely perfect definition of this relationship.” In 1875, many countries around the world signed a meter agreement, and this agreement established a procedure for coordinating metrological standards for the world scientific community through the International Bureau of Weights and Measures and the General Conference on Weights and Measures. The new international organization immediately began developing international standards for length and mass and transmitting copies of them to all participating countries.
Standards of length and mass, international prototypes.
The international prototypes of the standards of length and mass - the meter and the kilogram - were transferred for storage to the International Bureau of Weights and Measures, located in Sèvres, a suburb of Paris. The meter standard was a ruler made of a platinum alloy with 10% iridium, the cross-section of which was given a special cross-section to increase bending rigidity with a minimum volume of metal X -shape. In the groove of such a ruler there was a longitudinal flat surface, and the meter was defined as the distance between the centers of two lines drawn across the ruler at its ends, at a standard temperature of 0°
C. The mass of a cylinder made of the same platinum-iridium alloy as the standard meter, with a height and diameter of about 3.9 cm, was taken as the international prototype of the kilogram. The weight of this standard mass, equal to 1 kg at sea level at latitude 45°
, sometimes called kilogram-force. Thus, it can be used either as a standard of mass for an absolute system of units, or as a standard of force for a technical system of units in which one of the basic units is the unit of force. The international prototypes were selected from a large batch of identical standards produced simultaneously. Other standards of this batch were transferred to all participating countries as national prototypes (state primary standards), which are periodically returned to the International Bureau for comparison with international standards. Comparisons made at various times since then show that they do not show deviations (from international standards) beyond the limits of measurement accuracy.
International SI system.
The metric system was very favorably received by scientists of the 19th century. partly because it was proposed as an international system of units, partly because its units were theoretically assumed to be independently reproducible, and also because of its simplicity. Scientists began to develop new units for the various physical quantities they dealt with, based on the elementary laws of physics and linking these units to the metric units of length and mass. The latter increasingly conquered various European countries, in which previously many unrelated units for different quantities were in use. Although all countries that adopted the metric system of units had nearly the same standards for metric units, various discrepancies in derived units arose between different countries and different disciplines. In the field of electricity and magnetism, two separate systems of derived units emerged: electrostatic, based on the force with which two electric charges act on each other, and electromagnetic, based on the force of interaction between two hypothetical magnetic poles. The situation became even more complicated with the advent of the so-called system. practical electrical units introduced in the mid-19th century. by the British Association for the Advancement of Science to meet the demands of rapidly developing wire telegraph technology. Such practical units do not coincide with the units of both systems mentioned above, but differ from the units of the electromagnetic system only by factors equal to whole powers of ten. Thus, for such common electrical quantities as voltage, current and resistance, there were several options for accepted units of measurement, and each scientist, engineer, and teacher had to decide for himself which of these options was best for him to use. In connection with the development of electrical engineering in the second half of the 19th and first half of the 20th centuries. Practical units were increasingly used and eventually came to dominate the field.
To eliminate such confusion at the beginning of the 20th century. a proposal was put forward to combine practical electrical units with corresponding mechanical ones based on metric units of length and mass, and build some kind of coherent system. In 1960 XI The General Conference on Weights and Measures adopted a unified International System of Units (SI), defined the basic units of that system, and prescribed the use of certain derived units, “without prejudice to others that may be added in the future.” Thus, for the first time in history, an international coherent system of units was adopted by international agreement. It is now accepted as a legal system of units of measurement by most countries in the world. The International System of Units (SI) is a harmonized system that provides one and only one unit of measurement for any physical quantity, such as length, time, or force. Some of the units are given special names, an example is the unit of pressure pascal, while the names of others are derived from the names of the units from which they are derived, for example the unit of speed - meter per second. The basic units, together with two additional geometric ones, are presented in Table. 1. Derived units for which special names are adopted are given in table. 2. Of all the derived mechanical units, the most important are the unit of force newton, the unit of energy the joule and the unit of power the watt. Newton is defined as the force that imparts an acceleration of one meter per second squared to a mass of one kilogram. A joule is equal to the work done when the point of application of a force equal to one Newton moves a distance of one meter in the direction of the force. A watt is the power at which one joule of work is done in one second. Electrical and other derived units will be discussed below. The official definitions of major and minor units are as follows. A meter is the length of the path traveled by light in a vacuum in 1/299,792,458 of a second. This definition was adopted in October 1983. A kilogram is equal to the mass of the international prototype of the kilogram. A second is the duration of 9,192,631,770 periods of radiation oscillations corresponding to transitions between two levels of the hyperfine structure of the ground state of the cesium-133 atom. Kelvin is equal to 1/273.16 of the thermodynamic temperature of the triple point of water. A mole is equal to the amount of a substance that contains the same number of structural elements as atoms in the carbon-12 isotope weighing 0.012 kg. A radian is a plane angle between two radii of a circle, the length of the arc between which is equal to the radius. The steradian is equal to the solid angle with its vertex at the center of the sphere, cutting out on its surface an area equal to the area of a square with a side equal to the radius of the sphere. To form decimal multiples and submultiples, a number of prefixes and factors are prescribed, indicated in the table. 3.
|
Table 3. Prefixes and multipliers of the international system of units |
|||||
| exa | deci | ||||
| peta | centi | ||||
| tera | Milli | ||||
| giga | micro | ||||
| mega | nano | ||||
| kilo | pico | ||||
| hecto | femto | ||||
| soundboard | atto | ||||
Thus, a kilometer (km) is 1000 m, and a millimeter is 0.001 m. (These prefixes apply to all units, such as kilowatts, milliamps, etc.)
It was originally intended that one of the base units should be the gram, and this was reflected in the names of the units of mass, but nowadays the base unit is the kilogram. Instead of the name megagram, the word “ton” is used. In physics disciplines, such as measuring the wavelength of visible or infrared light, a millionth of a meter (micrometer) is often used. In spectroscopy, wavelengths are often expressed in angstroms (); An angstrom is equal to one tenth of a nanometer, i.e. 10 - 10 m. For radiation with a shorter wavelength, such as X-rays, in scientific publications it is allowed to use a picometer and an x-unit (1 x-unit. = 10 -13 m). A volume equal to 1000 cubic centimeters (one cubic decimeter) is called a liter (L).
Mass, length and time. All basic SI units, except the kilogram, are currently defined in terms of physical constants or phenomena that are considered immutable and reproducible with high accuracy. As for the kilogram, a way to implement it with the degree of reproducibility that is achieved in procedures for comparing various mass standards with the international prototype of the kilogram has not yet been found. Such a comparison can be made by weighing on a spring balance, the error of which does not exceed 1 H 10 -8 . Standards of multiple and submultiple units for a kilogram are established by combined weighing on scales.
Since the meter is defined in terms of the speed of light, it can be reproduced independently in any well-equipped laboratory. Thus, using the interference method, line and end length measures, which are used in workshops and laboratories, can be checked by comparing directly with the wavelength of light. The error with such methods under optimal conditions does not exceed one billionth ( 1 H 10 -9 ). With the development of laser technology, such measurements have become very simplified, and their range has expanded significantly. see also OPTICS.
Likewise, the second, according to its modern definition, can be independently realized in a competent laboratory in an atomic beam facility. The beam's atoms are excited by a high-frequency oscillator tuned to the atomic frequency, and an electronic circuit measures time by counting the periods of oscillation in the oscillator circuit. Such measurements can be carried out with an accuracy of the order of 1 H 10 -12 - much higher than was possible with previous definitions of the second, based on the rotation of the Earth and its revolution around the Sun. Time and its reciprocal, frequency, are unique in that their standards can be transmitted by radio. Thanks to this, anyone who has the appropriate radio receiving equipment can receive signals of exact time and reference frequency, almost no different in accuracy from those transmitted over the air. see also TIME.
Mechanics . Based on the units of length, mass and time, we can derive all the units used in mechanics, as shown above. If the basic units are meter, kilogram and second, then the system is called the ISS system of units; if - centimeter, gram and second, then - by the GHS system of units. The unit of force in the CGS system is called dyne, and the unit of work is called erg. Some units receive special names when they are used in special branches of science. For example, when measuring the strength of a gravitational field, the unit of acceleration in the CGS system is called a gal. There are a number of units with special names that are not included in any of the specified systems of units. Bar, a unit of pressure previously used in meteorology, is equal to 1,000,000 dynes/cm 2 . Horsepower, an obsolete unit of power still used in the British technical system of units, as well as in Russia, is approximately 746 watts.
Temperature and heat. Mechanical units do not allow solving all scientific and technical problems without involving any other relationships. Although the work done when moving a mass against the action of a force, and the kinetic energy of a certain mass are equivalent in nature to the thermal energy of a substance, it is more convenient to consider temperature and heat as separate quantities that do not depend on mechanical ones.
Thermodynamic temperature scale. The unit of thermodynamic temperature Kelvin (K), called kelvin, is determined by the triple point of water, i.e. the temperature at which water is in equilibrium with ice and steam. This temperature is taken to be 273.16 K, which determines the thermodynamic temperature scale. This scale, proposed by Kelvin, is based on the second law of thermodynamics. If there are two thermal reservoirs with a constant temperature and a reversible heat engine transferring heat from one of them to the other in accordance with the Carnot cycle, then the ratio of the thermodynamic temperatures of the two reservoirs is given byT 2 / T 1 = - Q 2 Q 1 where Q 2 and Q 1 - the amount of heat transferred to each of the reservoirs (the minus sign indicates that heat is taken from one of the reservoirs). Thus, if the temperature of the warmer reservoir is 273.16 K, and the heat taken from it is twice as much as the heat transferred to the other reservoir, then the temperature of the second reservoir is 136.58 K. If the temperature of the second reservoir is 0 K, then it no heat will be transferred at all, since all the gas energy has been converted into mechanical energy in the adiabatic expansion section of the cycle. This temperature is called absolute zero. The thermodynamic temperature commonly used in scientific research coincides with the temperature included in the equation of state of an ideal gasPV = RT, Where P- pressure, V- volume and R - gas constant. The equation shows that for an ideal gas, the product of volume and pressure is proportional to temperature. This law is not exactly satisfied for any of the real gases. But if corrections are made for virial forces, then the expansion of gases allows us to reproduce the thermodynamic temperature scale.
International temperature scale.
In accordance with the definition outlined above, temperature can be measured with very high accuracy (up to approximately 0.003 K near the triple point) by gas thermometry. A platinum resistance thermometer and a gas reservoir are placed in a thermally insulated chamber. When the chamber is heated, the electrical resistance of the thermometer increases and the gas pressure in the reservoir increases (in accordance with the equation of state), and when cooled, the opposite picture is observed. By measuring resistance and pressure simultaneously, you can calibrate the thermometer by gas pressure, which is proportional to temperature. The thermometer is then placed in a thermostat in which the liquid water can be kept in equilibrium with its solid and vapor phases. By measuring its electrical resistance at this temperature, a thermodynamic scale is obtained, since the temperature of the triple point is assigned a value equal to 273.16 K. There are two international temperature scales - Kelvin (K) and Celsius (C). Temperature on the Celsius scale is obtained from temperature on the Kelvin scale by subtracting 273.15 K from the latter. Accurate temperature measurements using gas thermometry require a lot of labor and time. Therefore, the International Practical Temperature Scale (IPTS) was introduced in 1968. Using this scale, thermometers of different types can be calibrated in the laboratory. This scale was established using a platinum resistance thermometer, a thermocouple and a radiation pyrometer, used in the temperature intervals between certain pairs of constant reference points (temperature benchmarks). The MPTS was supposed to correspond to the thermodynamic scale with the greatest possible accuracy, but, as it turned out later, its deviations were very significant.
Fahrenheit temperature scale. The Fahrenheit temperature scale, which is widely used in combination with the British technical system of units, as well as in non-scientific measurements in many countries, is usually determined by two constant reference points - the melting temperature of ice (32°F ) and water boiling (212°F ) at normal (atmospheric) pressure. Therefore, to get the Celsius temperature from the Fahrenheit temperature, you need to subtract 32 from the latter and multiply the result by 5/9.
Units of heat. Since heat is a form of energy, it can be measured in joules, and this metric unit has been adopted by international agreement. But since the amount of heat was once determined by the change in temperature of a certain amount of water, a unit called a calorie became widespread and is equal to the amount of heat required to increase the temperature of one gram of water by 1° C. Due to the fact that the heat capacity of water depends on temperature, it was necessary to clarify the calorie value. At least two different calories appeared - “thermochemical” (4.1840 J) and “steam” (4.1868 J). The “calorie” used in dietetics is actually a kilocalorie (1000 calories). The calorie is not an SI unit and has fallen into disuse in most fields of science and technology.
Electricity and magnetism. All commonly accepted electrical and magnetic units of measurement are based on the metric system. In accordance with modern definitions of electrical and magnetic units, they are all derived units, derived by certain physical formulas from the metric units of length, mass and time. Since most electrical and magnetic quantities are not so easy to measure using the standards mentioned, it was found that it is more convenient to establish, through appropriate experiments, derivative standards for some of the indicated quantities, and to measure others using such standards.
SI units. Below is a list of SI electrical and magnetic units.
The ampere, a unit of electric current, is one of the six SI base units. Ampere is the strength of a constant current, which, when passing through two parallel straight conductors of infinite length with a negligibly small circular cross-sectional area, located in a vacuum at a distance of 1 m from each other, would cause an interaction force equal to 2 on each section of the conductor 1 m long Ch 10 - 7 N.
Volt, a unit of potential difference and electromotive force. Volt - electrical voltage in a section of an electrical circuit with a direct current of 1 A with a power consumption of 1 W.
Coulomb, a unit of quantity of electricity (electric charge). Coulomb - the amount of electricity passing through the cross-section of a conductor at a constant current of 1 A in 1 s.
Farad, a unit of electrical capacitance. Farad is the capacitance of a capacitor on the plates of which, when charged at 1 C, an electric voltage of 1 V appears.
Henry, unit of inductance. Henry is equal to the inductance of the circuit in which a self-inductive emf of 1 V occurs when the current in this circuit changes uniformly by 1 A in 1 s.
Weber unit of magnetic flux. Weber is a magnetic flux, when it decreases to zero, an electric charge equal to 1 C flows in a circuit coupled with it, having a resistance of 1 Ohm.
Tesla, a unit of magnetic induction. Tesla is the magnetic induction of a uniform magnetic field in which the magnetic flux through a flat area of 1 m 2 , perpendicular to the induction lines, is equal to 1 Wb.
Practical standards. In practice, the ampere value is reproduced by actually measuring the force of interaction between the turns of wire carrying the current. Since electric current is a process that occurs over time, a current standard cannot be stored. In the same way, the value of the volt cannot be fixed in direct accordance with its definition, since it is difficult to reproduce the watt (unit of power) with the necessary accuracy by mechanical means. Therefore, the volt is reproduced in practice using a group of normal elements. In the United States, on July 1, 1972, legislation adopted a definition of the volt based on the Josephson effect on alternating current (the frequency of the alternating current between two superconducting plates is proportional to the external voltage). see also SUPERCONDUCTIVITY; ELECTRICITY AND MAGNETISM.
Light and illumination. Luminous intensity and illuminance units cannot be determined based on mechanical units alone. We can express the energy flux in a light wave in W/m 2 , and the intensity of the light wave is in V/m, as in the case of radio waves. But the perception of illumination is a psychophysical phenomenon in which not only the intensity of the light source is significant, but also the sensitivity of the human eye to the spectral distribution of this intensity.
By international agreement, the unit of luminous intensity is the candela (previously called a candle), equal to the luminous intensity in a given direction of a source emitting monochromatic radiation of frequency 540 H 10 12 Hz ( l = 555 nm), the energy intensity of light radiation in this direction is 1/683 W/sr. This roughly corresponds to the luminous intensity of a spermaceti candle, which once served as a standard.
If the luminous intensity of the source is one candela in all directions, then the total luminous flux is 4p lumens. Thus, if this source is located at the center of a sphere with a radius of 1 m, then the illumination of the inner surface of the sphere is equal to one lumen per square meter, i.e. one suite.
X-ray and gamma radiation, radioactivity. X-ray (R) is an obsolete unit of exposure dose of x-ray, gamma and photon radiation, equal to the amount of radiation that, taking into account secondary electron radiation, forms ions in 0.001 293 g of air that carry a charge equal to one unit of the CGS charge of each sign. The SI unit of absorbed radiation dose is the gray, equal to 1 J/kg. The standard for absorbed radiation dose is a setup with ionization chambers that measure the ionization produced by radiation.
Curie (Ci) is an obsolete unit of activity of a nuclide in a radioactive source. Curie is equal to the activity of a radioactive substance (drug), in which 3,700 Ch 10 10 acts of decay. In the SI system, the unit of isotope activity is the becquerel, equal to the activity of the nuclide in a radioactive source in which one decay event occurs in 1 s. Radioactivity standards are obtained by measuring the half-lives of small quantities of radioactive materials. Then, ionization chambers, Geiger counters, scintillation counters and other instruments for recording penetrating radiation are calibrated and verified using such standards. see also MEASUREMENTS AND WEIGHING; MEASURING INSTRUMENTS; ELECTRICAL MEASUREMENTS.
|
Table 2. DERIVATIVE SI UNITS WITH PROPER NAMES |
||||
|
Derived unit expression |
||||
|
Magnitude |
Name |
Designation | via other SI units | through major and supplementary SI units |
| Frequency | hertz | Hz | – | s -1 |
| Force | newton | N | – | m H kgH s -2 |
| Pressure | pascal | Pa | N/m 2 | m -1 H kg H s -2 |
| Energy, work, amount of heat | joule | J | N H m | m 2 H kg H s -2 |
| Power, energy flow | watt | W | J/s | m 2 H kg H s -3 |
| Amount of electricity, electric charge | pendant | Cl | A H s | With H A |
| Electrical voltage, electrical potential | volt | IN | W/A | m 2 H kg H s -3 H A -1 |
| Electrical capacity | farad | F | Cl/V | m -2 H kg -1 H s 4 H A 2 |
| Electrical resistance | ohm | Ohm | V/A | m 2 H kg H s -3 H A -2 |
| Electrical conductivity | Siemens | Cm | A/B | m -2 H kg -1 H s 3 H A 2 |
| Magnetic induction flux | weber | Wb | IN H s | m 2 H kg H s -2 H A -1 |
| Magnetic induction | tesla | T, Tl | Wb/m 2 | kg H s -2 H A -1 |
| Inductance | Henry | G, Gn | Wb/A | m 2 H kg H s -2 H A -2 |
| Light flow | lumen | lm | cd H Wed | |
| Illumination | luxury | OK | m 2 H cd H avg | |
| Radioactive source activity | becquerel | Bk | s -1 | s -1 |
| Absorbed radiation dose | Gray | Gr | J/kg | m 2 H s -2 |
|
Table 1. BASIC SI UNITS |
|||
|
Magnitude |
Designation |
||
| Name | Russian | international | |
| Length | meter | m | m |
| Weight | kilogram | kg | kg |
| Time | second | With | s |
| Electric power current | ampere | A | A |
| Thermodynamic temperature | kelvin | TO | K |
| The power of light | candela | cd | CD |
| Quantity of substance | mole | mole | mol |
|
ADDITIONAL SI UNITS |
|||
|
Magnitude |
Designation |
||
| Name | Russian | international | |
| Flat angle | radian | glad | rad |
| Solid angle | steradian | Wed | sr |
LITERATURE
Burdun G.D. Handbook of the International System of Units
. M., 1972
Dengub V.M., Smirnov V.G.Units of quantities(dictionary-reference book).
M., 1990
Unity of measurement implies consistency unit sizes of all sizes. This becomes obvious if we recall the possibility of measuring the same quantity by direct and indirect measurements. Such consistency is achieved by creating a system of units. But, although the advantages of a system of units compared to a set of separate units were realized a long time ago, the first system of units appeared only at the end of the 18th century. This was the famous metric system (meter, kilogram, second), approved on March 26, 1791 by the Constituent Assembly of France. The first scientifically based system of units, as a set of arbitrary basic units and derivative units dependent on them, was proposed in 1832 by K. Gauss. He built a system of units called absolute, based on three arbitrary units independent of each other: millimeter, milligram and second. The development of the Gauss system was the GGS system (centimeter, gram, second), which appeared in 1881, convenient for use in electromagnetic measurements, and its various modifications.
The development of industry and trade during the era of the first industrial revolution required the unification of units on an international scale. This process began on May 20, 1875, with the signing of the Meter Convention by 17 countries (including Russia, Germany, the USA, France, England), which was later joined by many countries. Under this convention, international cooperation in the field of metrology was established. In Sèvres, located in the suburbs of Paris, the International Bureau of Weights and Measures (BIPM) was created to carry out international metrological research and maintain international standards. To guide the BIPM, the International Committee of Weights and Measures (CIPM) was established, which includes advisory committees on units and a number of types of measurements. To resolve fundamental issues of international metrological cooperation, international conferences called the General Conference on Weights and Measures (GCPM) began to be held regularly. All countries that signed the Metric Convention received prototypes of international standards of length (meter) and mass (kilogram). Periodic comparisons of these national standards with international standards stored at the BIPM were also organized. Thus, the metric system of units received international recognition for the first time. However, after the signing of the Metric Convention, systems of units were developed for various areas of measurement - GHS, SGSE, SGSM, MTS, MKS, MKGSS. The problem of uniformity of measurements arises again, this time between different areas of measurement. And in 1954, the CGPM preliminary, and in October 1960, the XI CGPM finally adopted the International System of Units SI, which, with minor changes, is in force to the present day. At subsequent meetings of the CGPM, changes and additions were repeatedly made to it. Currently, the SI system of units is regulated by the ISO 31 standard and is essentially an international regulation that is mandatory for use. In our country, the ISO 31 standard has been approved as the state standard GOST 8.417-02.
SI system of units formed in accordance with the general principle of the formation of systems of units, which was proposed by K. Gauss in 1832. In accordance with it, all physical quantities are divided into two groups: quantities taken to be independent of other quantities, which are called basic quantities; all other quantities, called derivatives, which are expressed through basic and already defined derivative quantities using physical equations. The classification of units follows from this: units of basic quantities are the basic units of the system, and units of derived quantities are derived units.
So, first it is formed system of quantities — a set of quantities formed in accordance with the principle when some quantities are taken as independent, while others are functions of independent quantities. A quantity included in a system of quantities, conventionally accepted as independent of other quantities of this system, is called a basic quantity. A quantity included in a system of quantities and determined through basic and already defined derived quantities,is called a derivative quantity.
The unit of the basic quantity of a given system of quantities is called the basic unit. Derived unit— it is a unit of a derived quantity of a given system of quantities, formed in accordance with an equation connecting it with the basic units or with the basic units and already defined derived units.
In this way it is formed system of units of quantities— a set of basic and derived units of a given system of quantities.
Basic units of measurement. For each measured physical quantity, a corresponding unit of measurement must be provided. Thus, a separate unit of measurement is needed for weight, distance, volume, speed, etc., and each such unit can be determined by choosing one or another standard. The system of units turns out to be much more convenient if in it only a few units are selected as basic ones, and the rest are determined through the basic ones. So, if the unit of length is a meter, the standard of which is stored in the State Metrological Service, then the unit of area can be considered a square meter, the unit of volume is a cubic meter, the unit of speed is a meter per second, etc.
The convenience of such a system of units of measurement is that the mathematical relationships between the basic and derived units of the system are simpler. In this case, a unit of speed is a unit of distance (length) per unit of time, a unit of acceleration is a unit of change in speed per unit of time, a unit of force is a unit of acceleration per unit of mass, etc. In mathematical notation it looks like this: v = l/t, a = v/t, F = ma = ml/t2. The presented formulas show the “dimension” of the quantities under consideration, establishing relationships between units. (Similar formulas allow you to determine units for quantities such as pressure or electric current.) Such relationships are of a general nature and are valid regardless of what units (meter, foot or arshin) the length is measured in and what units are chosen for other quantities.