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| Experiments, experiments, theory, practice, problem solving. Additional materials for the lesson "Temperature. Thermometers" Single scale and mercury |
Long way thermometers
TemperatureTemperature is one of the most important indicators that is used in various branches of natural science and technology. In physics and chemistry, it is used as one of the main characteristics of the equilibrium state of an isolated system, in meteorology - as the main characteristic of climate and weather, in biology and medicine - as the most important quantity that determines vital functions. Even the ancient Greek philosopher Aristotle (384–322 BC) considered the concepts of heat and cold to be fundamental. Along with such qualities as dryness and humidity, these concepts characterized the four elements of "primary matter" - earth, water, air and fire. Although in those days and several centuries after they already talked about the degree of heat or cold (“warmer”, “hot”, “colder”), there were no quantitative measures. Approximately 2500 years ago, the ancient Greek physician Hippocrates (c. 460 - c. 370 BC) realized that the elevated temperature of the human body is a sign of illness. There was a problem in determining the normal temperature. One of the first attempts to introduce the concept of standard temperature was made by the ancient Roman physician Galen (129 - c. 200), who proposed to consider the temperature of a mixture of equal volumes of boiling water and ice to be “neutral”, and the temperatures of individual components (boiling water and melting ice) to be considered four degrees, respectively. warm and four degrees cold. It is probably to Galen that we owe the introduction of the term temper(to equalize), from which the word "temperature" is derived. However, the temperature began to be measured much later. Thermoscope and the first air thermometersThe history of temperature measurement has only a little more than four centuries. Based on the ability of air to expand when heated, which was described by the ancient Byzantine Greeks as early as the 2nd century BC. BC, several inventors created a thermoscope - the simplest device with a glass tube filled with water. It should be said that the Greeks (the first Europeans) got acquainted with glass as early as the 5th century, in the 13th century. the first glass Venetian mirrors appeared, by the 17th century. glasswork in Europe became quite developed, and in 1612 the first manual appeared "De arte vitraria"(“On the Art of Glassmaking”) by the Florentine Antonio Neri (died 1614). Glassmaking was especially developed in Italy. Therefore, it is not surprising that the first glass instruments appeared there. The first description of the thermoscope was included in the book of the Neapolitan naturalist, engaged in ceramics, glass, artificial precious stones and distillation, Giovanni Battista de la Porta (1535–1615) Magia Naturalis("Natural Magic"). The edition was published in 1558. In the 1590s the Italian physicist, mechanic, mathematician and astronomer Galileo Galilei (1564-1642), according to the testimony of his students Nelli and Viviani, built his glass thermobaroscope in Venice using a mixture of water and alcohol; measurements could be made with this instrument. Some sources say that Galileo used wine as a colored liquid. The working fluid was air, and temperature changes were determined by the volume of air in the device. The device was inaccurate, its readings depended on both temperature and pressure, but it allowed the column of liquid to be "dropped" by changing the air pressure. The description of this device was made in 1638 by Galileo's student Benadetto Castelli. Close communication between Santorio and Galileo makes it impossible to determine the contribution of each to their many technical innovations. Santorio is known for his monograph "De statica medicine"(“On the Medicine of Balance”), containing the results of his experimental research and withstood five editions. In 1612 Santorio in his work "Commentaria in artem medicinalem Galeni"("Notes on the Medical Art of Galen") first described the air thermometer. He also used a thermometer to measure the temperature of the human body (“patients clamp the flask with their hands, breathe on it under cover, take it in their mouth”), used a pendulum to measure the pulse rate. His method consisted in fixing the rate of fall of the thermometer readings during ten swings of the pendulum, it depended on external conditions and was inaccurate. Instruments similar to Galileo's thermoscope were made by the Dutch physicist, alchemist, mechanic, engraver and cartographer Cornelis Jacobson Drebbel (1572–1633) and the English mystic and medical philosopher Robert Fludd (1574–1637), who were supposedly familiar with the work of Florentine scientists. It was Drebbel's device that was first (in 1636) called a "thermometer". It looked like a U-shaped tube with two reservoirs. While working on the liquid for his thermometer, Drebbel discovered a way to make bright carmine colors. Fludd, in turn, described the air thermometer. First liquid thermometersThe next small but important step towards the transformation of the thermoscope into a modern liquid thermometer was the use of a liquid and a glass tube sealed at one end as a working medium. The thermal expansion coefficients of liquids are less than those of gases, but the volume of a liquid does not change with a change in external pressure. This step was taken around 1654 in the workshops of the Grand Duke of Tuscany, Ferdinand II de' Medici (1610-1670). Meanwhile, systematic meteorological measurements began in various European countries. Each scientist at that time used his own temperature scale, and the measurement results that have come down to us can neither be compared with each other nor connected with modern degrees. The concept of a temperature degree and reference points of the temperature scale apparently appeared in several countries as early as the 17th century. Masters applied 50 divisions by eye so that at the temperature of melting snow the alcohol column did not fall below the 10th division, and in the sun it did not rise above the 40th division. One of the first attempts to calibrate and standardize thermometers was made in October 1663 in London. The members of the Royal Society agreed to use one of the alcohol thermometers made by the physicist, mechanic, architect and inventor Robert Hooke (1635–1703) as a standard and to compare the readings of other thermometers with it. Hooke introduced a red pigment into alcohol, the scale was divided into 500 parts. He also invented the minima thermometer (showing the lowest temperature). The Dutch theoretical physicist, mathematician, astronomer and inventor Christian Huygens (1629–1695) in 1665 together with R. Hooke suggested using the temperatures of melting ice and boiling water to create a temperature scale. The first intelligible meteorological records were recorded using the Hooke–Huygens scale. The first description of a real liquid thermometer appeared in 1667 in the publication of the Accademia del Cimento * "Essays on the natural scientific activities of the Academy of Experiments." The first experiments in the field of calorimetry were carried out and described at the Academy. It has been shown that under vacuum water boils at a lower temperature than at atmospheric pressure, and that when it freezes it expands. "Florence thermometers" were widely used in England (introduced by R. Boyle) and in France (distributed thanks to the astronomer I. Bullo). The author of the well-known Russian monograph "Concepts and Fundamentals of Thermodynamics" (1970) I.R. Krichevsky believes that it was the work of the Academy that laid the foundation for the use of liquid thermometers. One of the members of the Academy, mathematician and physicist Carlo Renaldini (1615–1698) in his essay Philosophia naturalis("Natural Philosophy"), published in 1694, proposed to take the temperatures of melting ice and boiling water as reference points. Born in the German city of Magdeburg, a mechanical engineer, electrical engineer, astronomer, inventor of the air pump Otto von Guericke (1602–1686), who became famous for his experience with the Magdeburg hemispheres, also dealt with thermometers. In 1672, he built a water-alcohol device several meters high with a scale that had eight divisions: from “very cold” to “very hot”. The dimensions of the structure, it must be admitted, did not advance thermometry. Guericke's gigantomania found followers in the United States three centuries later. The world's largest thermometer, 40.8 m (134 ft) tall, was built in 1991 to commemorate the record high temperature reached in California's Death Valley in 1913: +56.7 °C (134 °F). A three-way thermometer is located in the small town of Baker near Nevada. The first accurate thermometers that came into wide use were made by the German physicist Daniel Gabriel Fahrenheit (1686–1736). The inventor was born on the territory of present-day Poland, in Gdansk (then Danzig), orphaned early, began to study trading in Amsterdam, but did not finish his studies and, carried away by physics, began to visit laboratories and workshops in Germany, Holland and England. Since 1717 he lived in Holland, where he had a glass-blowing workshop and was engaged in the manufacture of precise meteorological instruments - barometers, altimeters, hygrometers and thermometers. In 1709 he made an alcohol thermometer, and in 1714 a mercury thermometer. Mercury turned out to be a very convenient working fluid, since it had a more linear dependence of volume on temperature than alcohol, it was heated much faster than alcohol and could be used at much higher temperatures. Fahrenheit developed a new method for purifying mercury and used a cylinder instead of a ball for mercury. In addition, to improve the accuracy of thermometers, Fahrenheit, who owned glassblowing skills, began to use glass with the lowest coefficient of thermal expansion. Only in the area of low temperatures mercury (freezing point -38.86 °C) was inferior to alcohol (freezing point -114.15 °C). Since 1718, Fahrenheit lectured in Amsterdam on chemistry, in 1724 he became a member of the Royal Society, although he did not receive a degree and published only one collection of research articles. For his thermometers, Fahrenheit first used a modified scale adopted by the Danish physicist Olaf Römer (1644–1710) and proposed by the English mathematician, mechanic, astronomer, and physicist Isaac Newton (1643–1727) in 1701. Newton's own initial attempts to develop a temperature scale proved naive and were abandoned almost immediately. It was proposed to take the air temperature in winter and the temperature of glowing coals as reference points. Then Newton used the melting point of snow and the body temperature of a healthy person, linseed oil as a working medium, and broke the scale (based on the model of 12 months a year and 12 hours a day until noon) by 12 degrees (according to other sources, by 32 degrees) . In this case, the calibration was carried out by mixing certain amounts of boiling and freshly thawed water. But this method was also unacceptable. Newton was not the first to use oil: back in 1688, the French physicist Dalence used the melting point of cow butter as a reference point for calibrating alcohol thermometers. If this technique had been preserved, Russia and France would have had different temperature scales: both melted butter common in Russia and the famous Vologda butter differ in composition from European varieties. The observant Roemer noticed that his pendulum clocks run slower in summer than in winter, and the divisions of the scales of his astronomical instruments are greater in summer than in winter. To improve the accuracy of measurements of time and astronomical parameters, it was necessary to carry out these measurements at the same temperatures and, therefore, to have an accurate thermometer. Roemer, like Newton, used two reference points: the normal temperature of the human body and the melting temperature of ice (the working fluid was fortified red wine or a 40% alcohol solution tinted with saffron in an 18-inch tube). Fahrenheit added a third point to them, which corresponded to the lowest temperature reached then in a mixture of water-ice-ammonia. Having achieved significantly higher measurement accuracy with his mercury thermometer, Fahrenheit divided each degree of Roemer into four and took three points as reference points for his temperature scale: the temperature of the salt mixture of water with ice (0 ° F), the body temperature of a healthy person (96 ° F) and the melting temperature of ice (32 °F), the latter being considered the control. Here is how he wrote about it in an article published in the magazine Philosophical Transaction"(1724, There is a legend that Fahrenheit took the temperature to which the air cooled in the winter of 1708/09 in his hometown of Danzig as the lowest point on the Fahrenheit scale. One can also find statements that he believed that a person dies from cold at 0 ° F and from heat stroke at After some trial and error, Fahrenheit came up with a very comfortable temperature scale. The boiling point of water turned out to be 212 °F on the accepted scale, and the entire temperature range of the liquid state of water was 180 °F. The rationale for this scale was the absence of negative degrees. Subsequently, after a series of precise measurements, Fahrenheit found that the boiling point varies with atmospheric pressure. This allowed him to create a hypsothermometer - a device for measuring atmospheric pressure by the boiling point of water. He also belongs to the primacy in the discovery of the phenomenon of supercooling of liquids. Fahrenheit's work marked the beginning of thermometry, and then thermochemistry and thermodynamics. The Fahrenheit scale was adopted as official in many countries (in England since 1777), only the normal temperature of the human body was corrected to 98.6 o F. Now this scale is used only in the USA and Jamaica, other countries in 1960- 1970s and 1970s switched to the Celsius scale. The thermometer was introduced into wide medical practice by the Dutch professor of medicine, botany and chemistry, the founder of a scientific clinic, Hermann Boerhaave (1668–1738), his student Gerard van Swieten (1700–1772), the Austrian physician Anton de Haen (1704–1776) and, regardless of them by the Englishman George Martin. The founder of the Vienna School of Medicine, Haen, found that the temperature of a healthy person rises and falls twice during the day. Being a supporter of the theory of evolution, he explained this by the fact that the ancestors of man - reptiles that lived by the sea - changed their temperature in accordance with the ebb and flow. However, his work was forgotten for a long time. Martin wrote in one of his books that his contemporaries argued whether the melting temperature of ice changes with height, and to establish the truth, they transported a thermometer from England to Italy. It is no less surprising that scientists who became famous in various fields of knowledge later became interested in measuring the temperature of the human body: A. Lavoisier and P. Laplace, J. Dalton and G. Davy, D. Joule and P. Dulong, W. Thomson and A. Becquerel , J. Foucault and G. Helmholtz. "A lot of mercury has leaked" since then. The almost three hundred year era of widespread use of mercury thermometers seems to be coming to an end soon due to the toxicity of liquid metal: in European countries, where people's safety is becoming more and more important, laws have been passed to restrict and prohibit the production of such thermometers. * Founded in Florence in 1657 by students of Galileo under the auspices of Ferdinand II Medici and his brother Leopoldo, the Accademia del Cimento did not last long, but became the prototype of the Royal Society, the Paris Academy of Sciences and other European academies. It was conceived to promote scientific knowledge and expand collective activities for their development. Printed with a continuation |
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Water temperature, 0 C |
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Water temperature, 0 C |
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We build a graph of temperature versus time.
Research Conclusion :
Solidification of water takes place at a constant temperature of 0 0 C. The temperature does not change during the process of solidification.
2.Study of snow (ice) melting processes.
Purpose: To investigate the process of melting snow (ice). Find out the conditions for melting snow.
Equipment: glass with snow, thermometer, stopwatch.
Research progress.
We observe the melting of snow in the physics classroom of the school.
We lower the thermometer into a vessel with snow and observe temperature changes. Using a stopwatch, we monitor the melting time.
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Temperature, 0 C |
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Temperature, 0 C |
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Research Conclusion :
Ice is a crystalline substance.
Snow melts at a constant temperature of 0 0 C. The temperature does not change during the melting process.
3. Research of paraffin melting process.
Purpose: To investigate the process of paraffin melting. Find out the conditions for melting paraffin.
Research progress.
We observe the melting of paraffin in the physics room of the school.
The thermometer is in a test tube with paraffin. We place the test tube in hot water and observe the temperature changes. Using a stopwatch, we monitor the melting time.
The results of observations are entered in the table:
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Temperature, 0 C |
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Research Conclusion :
Paraffin is an amorphous body. When melting paraffin, the temperature gradually increases.
4. Study of the paraffin hardening process.
Purpose: To investigate the process of solidification of paraffin. Find out the conditions for curing paraffin.
Equipment: a test tube with paraffin, a thermometer, a stopwatch, a vessel with hot water.
Research progress.
We observe paraffin solidification in the physics classroom of the school.
The thermometer is in a test tube with paraffin. Test tube in hot water and observe temperature changes. Using a stopwatch, we monitor the melting time.
The results of observations are entered in the table:
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Temperature, 0 C |
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Research Conclusion :
Paraffin is an amorphous body. As the paraffin hardens, the temperature gradually decreases.
In the course of the study, we found that the processes of melting and solidification of crystals and amorphous bodies proceed differently.
Crystals have a certain melting and solidification temperature. We found that for water the melting and solidification temperature is 0 0 C. While the process of melting or solidification is in progress, the temperature of the water did not change. But in order for water to solidify, it is necessary that the air temperature be less than 0 0 C. In order for ice to melt, it is necessary that the air temperature be greater than 0 0 C.
Amorphous bodies do not have a specific melting and solidification temperature. When amorphous substances are heated, they gradually melt, while their temperature rises. When cooled, they harden, while their temperature decreases.
3. Find the body weight P = ρgV
4. Determine the pressure exerted by the body on a horizontal surface P = , where F=P
Experimental work No. 12
Topic: "Investigation of the dependence of thermometer readings on external conditions."
Target: investigate the dependence of the thermometer readings depending on the external conditions: whether the sun's rays fall on the thermometer or whether it is in the shade, what substrate the thermometer lies on, what color screen the thermometer covers from the sun's rays.
Tasks:
Educational: education of accuracy, ability to work in a team;
Equipment: table lamp, thermometer, sheets of white and black paper.
What is the temperature of the air in the room and on the street people are interested in every day. There is a thermometer for measuring air temperature in almost every home, but not every person knows how to use it correctly. Firstly, many do not understand the very task of measuring air temperature. This misunderstanding is especially evident on hot summer days. When meteorologists report that the air temperature in the shade reached 32°C, many people "specify" something like this: "And in the sun the thermometer went beyond 50°C!" Do such clarifications make sense? To answer this question, perform the following experimental study and draw your own conclusions.
Progress:
Experience 1. Measure the air temperature "in the sun" and "in the shade". Use a table lamp as the "Sun".
The first time, place the thermometer at a distance of 15-20 cm from the lamp on the table, the second time, without changing the location of the lamp relative to the thermometer, create a "shadow" with a sheet of paper, placing it near the lamp. Record the thermometer readings.
Experiment 2. Perform temperature measurements "in the sun" under the conditions of using first a dark, then a light substrate under the thermometer. To do this, first place the thermometer on a sheet of white paper, the second time on a sheet of black paper. Record the thermometer readings.
Experiment 3. Perform measurements "in the shade" by blocking the light from the lamp with a sheet of white paper placed directly on the thermometer. Record the thermometer reading. Repeat the experiment, replacing the white paper with black paper.
Consider the results of the experiments performed and draw conclusions, where and how should a thermometer be mounted outside the window to measure the air temperature on the street?
A series of experiments, when properly performed, gives the following results.
Experience 1 shows that the readings of the thermometer “in the sun” are noticeably higher than its readings “in the shade”. This fact must receive the following explanation. In the absence of sunlight, the temperatures of the air and the table are the same. As a result of heat exchange with the table and air, the thermometer comes into thermal equilibrium with them and shows the air temperature.
When the "sun" is not covered by a sheet of paper, under the action of the absorbed radiation of the "sun" the temperature of the table rises, and the transparent air is almost not heated by this radiation. The thermometer, on the one hand, carries out heat exchange with the surface of the table, and on the other hand, with air. As a result, its temperature is higher than the air temperature, but lower than the surface temperature of the table. What then is the meaning of the readings of the thermometer “in the sun”?
A stubborn lover of air temperature measurements “in the sun” may object to this that he is not interested in the air temperature “in the shade”, when he himself is “in the sun”. Let it not be the air temperature, just the readings of the thermometer “in the sun”, but it is they that interest him. In this case, the results of experiment 2 will be useful to him.
Experiment 2 shows that on white paper, which reflects light well, the readings of the thermometer are much less than on black paper, which absorbs light radiation well and heats up more. Therefore, there is no unequivocal answer to the question about the readings of the thermometer “in the sun”. The result will strongly depend on the color of the substrate under the thermometer, the color and structure of the surface of the thermometer cylinder, and the presence or absence of wind.
The air temperature outside, when measured far from objects heated by solar radiation and with the exclusion of direct exposure to radiation on the thermometer, is the same “in the sun” and “in the shade”, this is just the air temperature. But it should really be measured only “in the shade”.
But creating a "shadow" for a thermometer on a sunny day is also not an easy task. This is confirmed by the results of experiment 3. They show that when the screen is close to the thermometer, the heating of the screen by solar radiation will lead to significant errors in measuring the air temperature on a sunny day. The temperature rise will be especially large when the screen is dark, since such a screen absorbs almost all the energy of the solar radiation incident on it, and much less when the screen is white, since such a screen reflects almost all the energy of the solar radiation incident on it.
After such an experimental study, it is necessary to discuss a practically important question: how, in practice, is it necessary to measure the air temperature in the street? The answer to this question might be something like this. If the apartment has a window facing north, then it is behind this window that you need to strengthen the street thermometer. If there is no such window in the apartment, the thermometer should be placed as far as possible from the walls heated by the sun, opposite the weakly heated window panes. The thermometer cylinder must be protected from heating by solar radiation. The results of experiment 3 show that when trying to protect the thermometer from solar radiation, the screen itself heats up and heats the thermometer. Since the white screen heats up less, the protective screen should be light and should be located at a sufficient distance from the thermometer.
Similarly, one can investigate the dependence of the readings of a room thermometer on its location. The result of homework should be the establishment of the fact that the readings of a room thermometer depend on its location in the room. If we are interested in the air temperature in the room, then it is necessary to exclude the influence of heated bodies and solar radiation on it. Direct sunlight should not fall on the thermometer; the thermometer should not be placed near heating and lighting devices. Do not hang a thermometer on the outer wall of a room that has an increased temperature in summer and a lower temperature in winter relative to the air temperature in the room.
Experimental work No. 13
Topic: "Determining the percentage of snow in water."
Target: Determine the percentage of snow in the water.
Tasks:
Educational: formation of the ability to combine knowledge and practical skills;
Developing: development of logical thinking, cognitive interest.
Equipment: calorimeter, thermometer, beaker, vessel with room water, mixture of snow and water, calorimetric body.
First option
Progress:
1. So much water is poured into the calorimeter with the mixture so that all the snow melts. The temperature of the resulting water was t=0.
2. Let's write the heat balance equation for this case:
m1 \u003d cm3 (t2-t1), where c is the specific heat of water, is the specific heat of ice melting, m1 is the mass of snow, m2 is the mass of water in snow, m3 is the mass of infused water, t is the temperature of infused water.
Hence = 
Desired percentage =;
3. The value m1 + m2 can be determined by pouring all the water from the calorimeter into the measuring cylinder and measuring the total mass of water m. Since m= m1 + m2 + m3, then
m1 + m2 = m - m3. Hence,
= 
Second option
Equipment: calorimeter, thermometer, scales and weights, a glass of warm water, a lump of wet snow, a calorimetric body.
Progress:
1. Weigh an empty calorimeter, and then a calorimeter with a lump of wet snow. By the difference, we determine the mass of a lump of wet snow (m).
The lump contains *x grams of water and *(100 - x) grams of snow, where x is the percentage of water in the lump.
Wet snow temperature 0.
2. Now we add so much warm water (mw) to the calorimeter with a lump of wet snow so that all the snow melts, having previously measured the temperature of warm water (to).
3. We weigh the calorimeter with water and melted snow and, by the difference in weights, determine the mass of warm water added (mw).
4. We measure the final temperature with a thermometer (tocm.).
5. Let's write the heat balance equation:
cmv t \u003d * (100 - x) + c (m + mv) to cm.,
Where c is the specific heat capacity of water-4200J / kg , - specific heat of snow melting
3.3 *105 J/kg.
6. From the resulting equation, we express
X=100 - 
Experimental work No. 14
Topic: "Determination of the heat of fusion of ice."
Target: determine the heat of fusion of ice .
Tasks:
Educational: formation of the ability to combine knowledge and practical skills;
Educational: education of accuracy, ability to work in a team;
Developing: development of logical thinking, cognitive interest.
Equipment: thermometer, water, ice, measuring cylinder.
Progress:
1. Put a piece of ice into an empty vessel and pour enough water from the measuring cylinder into it to melt all the ice.
2. In this case, the heat balance equation can be written simply:
St1 (t1 - t2) = t2
where m2 is the mass of ice, mx is the mass of poured water, tx is the initial water temperature, t2 is the final water temperature equal to 0 °C, K is the specific heat of ice melting. From the above equation we find:
3. The mass of ice can be determined by draining the resulting water into a measuring cylinder and measuring the total mass of water and ice:
М = + Т2 = ρаod, Vtot.
Since m2 \u003d M - m1, then
Experimental work No. 15
Target: using the proposed equipment and a table of dependence of saturated steam pressure on temperature, determine the absolute and relative humidity of the air in the room.
Tasks:
Educational: formation of the ability to combine knowledge and practical skills;
Educational: education of accuracy, ability to work in a team;
Developing: development of logical thinking, cognitive interest.
Equipment: glass, thermometer, ice, water.
Progress:
1. The absolute humidity of the air is easiest to determine by the dew point. To measure the dew point, you must first measure the temperature t1 of the air. Then take an ordinary glass beaker, pour some water into it at room temperature and place a thermometer in the water.
2. In another vessel, you need to prepare a mixture of water with ice and from this vessel add a little cold water to a glass with water and a thermometer until dew appears on the walls of the glass. You need to look at the wall of the glass opposite the water level in the glass. When the dew point is reached, the wall of the glass below the water level becomes opaque due to the many small dew drops condensed on the glass. At this point, you need to take the readings t2 of the thermometer.
3. Based on the value of temperature t2 - the dew point - one can determine from the table the density ρ of saturated steam at temperature t2. This will be the absolute humidity of the atmospheric air. Then you can find the value of the density r0 of saturated steam at temperature t1 from the table. Based on the found values of density r of saturated steam at temperature t2 and density ρ0 of saturated steam at room temperature t1, relative air humidity j is determined.
Errors of measuring instruments
Measuring |
Measurement limit |
Value of division |
Instrumental error |
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Ruler student | ||||
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Drawing ruler | ||||
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Ruler instrumental | ||||
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Demo ruler | ||||
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Measuring tape | ||||
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Beaker | ||||
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Scales for training | ||||
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Set of weights G-4-211.10 | ||||
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Weights for laboratory | ||||
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School caliper | ||||
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Micrometer | ||||
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Training dynamometer | ||||
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Stopwatch electronic KARSER |
±0.01 s (0.2 s subject to subjective error). |
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Aneroid barometer |
780 mm. rt. Art. |
1 mm. rt. Art. |
±3 mm. rt. Art. |
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Laboratory thermometer | ||||
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Manometer open demonstration |
Density of liquids, metals and alloys, solids and materials.
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ρ, kg/m3 |
All we need now is snow, a cup, a thermometer, and a little patience. We will bring a cup of snow from the cold, put it in a warm, but not hot place, immerse a thermometer in the snow and observe the temperature. At first, the column of mercury will creep up relatively quickly. The snow is still dry. When it reaches zero, the mercury column will stop. From that moment on, the snow begins to melt. Water appears at the bottom of the cup, but the thermometer still reads zero. By constantly stirring the snow, it is easy to make sure that until all of it has melted, the mercury will not budge.
What caused the temperature to stop and just at the time when the snow turns into water? The heat supplied to the cup is entirely spent on the destruction of snowflake crystals. And as soon as the last crystal is destroyed, the temperature of the water will begin to rise.
The same phenomenon can be observed during the melting of any other crystalline substances. They all require some amount of heat to go from solid to liquid. This quantity, quite specific for each substance, is called the heat of fusion.
The value of the heat of fusion for different substances is different. And right here, when we start comparing the specific heats of fusion for various substances, water again stands out among them. Like specific heat capacity, the specific heat of fusion of ice far exceeds the heat of fusion of any other substance.
To melt one gram of benzene, you need 30 calories, the heat of fusion of tin is 13 calories, lead - about 6 calories, zinc - 28, copper - 42 calories. And to turn ice into water at zero degrees, you need 80 calories! This amount of heat is enough to raise the temperature of one gram of liquid water from 20 degrees to boiling. Only one metal, aluminum, has a specific heat of fusion that exceeds that of ice.
So, water at zero degrees differs from ice at the same temperature in that each gram of water contains 80 calories more heat than a gram of ice.
Now, knowing how high the heat of fusion of ice is, we see that we have no reason to complain sometimes that the ice melts "too fast". If ice had the same heat of fusion as most other bodies, it would melt several times faster.
In the life of our planet, the melting of snow and ice is of absolutely exceptional importance in its importance. It must be remembered that the ice sheet alone occupies more than three percent of the entire earth's surface, or 11 percent of the entire land. In the region of the south pole lies the huge continent of Antarctica, larger than Europe and Australia combined, covered with a continuous layer of ice. Permafrost reigns over millions of square kilometers of land. Only glaciers and permafrost make up a fifth of the land mass. To this we must add another surface covered with snow in winter. And then we can say that from one quarter to one third of the land is always covered with ice and snow. For several months of the year, this area exceeds half of the entire landmass.
It is clear that huge masses of frozen water cannot but affect the Earth's climate. What a colossal amount of solar heat is spent just to melt one snow cover in spring! Indeed, on average, it reaches about 60 centimeters in thickness, and for each gram you need to spend 80 calories. But the sun is such a powerful source of energy that in our latitudes it can do this job sometimes in a few days. And it is hard to imagine what kind of high water would await us if the ice had, for example, such a heat of fusion as lead. All the snow could melt in one day or even in a few hours, and then the rivers that overflowed to extraordinary sizes would wash away the most fertile layer of soil and plants from the surface of the earth, bringing innumerable disasters to all life on Earth.
When ice melts, it absorbs a huge amount of heat. The same amount of heat is given off by water when it freezes. If water had a low heat of fusion, then our rivers, lakes and seas would probably freeze after the first frost.
So, to the large heat capacity of water, another remarkable feature was added - a large heat of fusion.
Thermometer
Thermometer (Greek θέρμη - heat; μετρέω - I measure) - a device for measuring the temperature of air, soil, water, and so on. There are several types of thermometers:liquid; mechanical; electronic; optical; gas; infrared.
Galileo is considered to be the inventor of the thermometer: in his own writings there is no description of this device, but his students, Nelly and Viviani, testified that already in 1597 he made something like a thermobaroscope (thermoscope). Galileo studied at this time the work of Heron of Alexandria, who already described a similar device, but not for measuring degrees of heat, but for raising water by heating. The thermoscope was a small glass ball with a glass tube soldered to it. The ball was slightly heated and the end of the tube was lowered into a vessel with water. After some time, the air in the ball cooled, its pressure decreased, and the water, under the action of atmospheric pressure, rose up in the tube to a certain height. Subsequently, with warming, the air pressure in the ball increased and the water level in the tube decreased; when cooled, the water in it rose. With the help of a thermoscope, it was possible to judge only about the change in the degree of heating of the body: it did not show the numerical values of the temperature, since it did not have a scale. In addition, the water level in the tube depended not only on temperature, but also on atmospheric pressure. In 1657 Galileo's thermoscope was improved by Florentine scientists. They fitted the instrument with a scale of beads and bled the air out of the tank (ball) and tube. This made it possible not only qualitatively, but also quantitatively to compare the temperatures of bodies. Subsequently, the thermoscope was changed: it was turned upside down, and brandy was poured into the tube instead of water and the vessel was removed. The operation of this device was based on the expansion of bodies; the temperatures of the hottest summer and coldest winter days were taken as "permanent" points. All these thermometers were air and consisted of a vessel with a tube containing air, separated from the atmosphere by a column of water, they changed their readings both from temperature changes and from changes in atmospheric pressure.
Liquid thermometers are described for the first time in 1667 "Saggi di naturale esperienze fatte nell'Accademia del Cimento", where they are referred to as objects long made by skilled artisans, called "Confia", warming the glass on a fanned lamp fire and making amazing and very delicate products from it. At first these thermometers were filled with water, but they burst when it froze; they began to use wine spirit for this in 1654 according to the idea of the Grand Duke of Tuscany Ferdinand II. Florentine thermometers have survived in several copies to our time in the Galilean Museum, in Florence; their preparation is described in detail.
First, the master had to make divisions on the tube, considering its relative dimensions and the size of the ball: divisions were applied with melted enamel on a tube heated on a lamp, every tenth was indicated by a white dot, and others by black. They usually made 50 divisions in such a way that when the snow melted, the alcohol did not fall below 10, and in the sun it did not rise above 40. Good craftsmen made such thermometers so successfully that they all showed the same temperature value under the same conditions, but this is not it was possible to achieve if the tube was divided into 100 or 300 parts in order to obtain greater accuracy. The thermometers were filled by heating the bulb and lowering the end of the tube into alcohol; filling was completed using a glass funnel with a thinly drawn end that freely entered a fairly wide tube. After adjusting the amount of liquid, the opening of the tube was sealed with sealing wax, called "hermetic". From this it is clear that these thermometers were large and could serve to determine the temperature of the air, but were still inconvenient for other, more diverse experiments, and the degrees of different thermometers were not comparable with each other.
Galileo thermometer
In 1703 Amonton ( Guillaume Amontons) in Paris improved the air thermometer, measuring not the expansion, but the increase in the elasticity of air reduced to the same volume at different temperatures by pouring mercury into an open knee; barometric pressure and its changes were taken into account. The zero of such a scale was supposed to be “that significant degree of cold” at which the air loses all its elasticity (that is, the modern absolute zero), and the second constant point was the boiling point of water. The influence of atmospheric pressure on the boiling point was not yet known to Amonton, and the air in his thermometer was not freed from water gases; therefore, from his data, absolute zero is obtained at −239.5° Celsius. Another Amonton air thermometer, made very imperfectly, was independent of changes in atmospheric pressure: it was a siphon barometer, the open knee of which was extended upwards, filled from below with a strong solution of potash, from above with oil and ended in a sealed reservoir of air.
The modern form of the thermometer was given by Fahrenheit and described his method of preparation in 1723. Initially, he also filled his tubes with alcohol and only finally switched to mercury. He set the zero of his scale at the temperature of a mixture of snow with ammonia or table salt, at the temperature of the “beginning of freezing of water” he showed 32 °, and the body temperature of a healthy person in the mouth or under the arm was equivalent to 96 °. Subsequently, he found that water boils at 212° and this temperature was always the same in the same state of the barometer. The surviving copies of Fahrenheit thermometers are distinguished by their meticulous workmanship.
Mercury thermometer with Fahrenheit scale
The Swedish astronomer, geologist and meteorologist Anders Celsius finally set both permanent points, melting ice and boiling water, in 1742. But initially he set 0 ° at the boiling point, and 100 ° at the freezing point. In his work Observations of two persistent degrees on a thermometer, Celsius spoke about his experiments showing that the melting point of ice (100 °) does not depend on pressure. He also determined, with amazing accuracy, how the boiling point of water varied with atmospheric pressure. He suggested that the 0 mark (the boiling point of water) could be calibrated, knowing at what level relative to the sea is the thermometer.
Later, after the death of Celsius, his contemporaries and compatriots, the botanist Carl Linnaeus and the astronomer Morten Strömer, used this scale upside down (for 0 ° they began to take the melting point of ice, and for 100 ° - the boiling point of water). In this form, the scale turned out to be very convenient, became widespread and is used to this day.
Liquid thermometers are based on the principle of changing the volume of liquid that is poured into the thermometer (usually alcohol or mercury) as the ambient temperature changes. In connection with the ban on the use of mercury due to its health hazard in many areas activities are looking for alternative fillings for household thermometers. For example, galinstan alloy can become such a replacement. Other types of thermometers are also increasingly being used.
Mercury medical thermometer
Mechanical thermometers of this type operate on the same principle as liquid ones, but a metal spiral or bimetal tape is usually used as a sensor.
Window mechanical thermometer
There are also electronic thermometers. The principle of operation of electronic thermometers is based on the change in the resistance of the conductor when the ambient temperature changes. Electronic thermometers of a wider range are based on thermocouples (contact between metals with different electronegativity creates a contact potential difference depending on the temperature). The most accurate and stable over time are resistance thermometers based on platinum wire or platinum sputtering on ceramics. The most common are PT100 (resistance at 0 °C - 100Ω) PT1000 (resistance at 0 °C - 1000Ω) (IEC751). The dependence on temperature is almost linear and obeys a quadratic law at positive temperatures and a 4th degree equation at negative ones (the corresponding constants are very small, and in the first approximation this dependence can be considered linear). Temperature range -200 - +850 °C.
Medical electronic thermometer
Optical thermometers allow you to record the temperature due to the change in the level of luminosity, spectrum and other parameters when the temperature changes. For example, infrared body temperature meters. An infrared thermometer allows you to measure temperature without direct contact with a person. In some countries, there has long been a tendency to abandon mercury thermometers in favor of infrared, not only in medical institutions, but also at the household level.
Infrared thermometer
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