For two whole years, the Swedish astronomer Anders Celsius tested the thermometer created earlier by the French zoologist and metallurgist René Antoine Reaumur. Experiments Celsius pr

Temperature scales. There are several graduated temperature scales, and the freezing and boiling temperatures of water are usually taken as reference points. Now the most common scale in the world is the Celsius scale. In 1742, Swedish astronomer Anders Celsius proposed a 100-degree thermometer scale in which 0 degrees is the boiling point of water at normal atmospheric pressure and 100 degrees is the melting temperature of ice. The scale division is 1/100 of this difference. When thermometers began to be used, it turned out to be more convenient to swap 0 and 100 degrees. Perhaps Carl Linnaeus participated in this (he taught medicine and natural science at the same Uppsala University where Celsius taught astronomy) who back in 1838 proposed taking the melting temperature of ice as 0 temperature, but it seems he did not think of a second reference point. To date, the Celsius scale has changed somewhat: 0°C is still taken to be the melting temperature of ice at normal pressure which does not really depend on pressure. But the boiling point of water at atmospheric pressure is now 99,975°C, which does not affect the measurement accuracy of almost all thermometers except special precision ones. The Fahrenheit temperature scales of Kelvin Reaumur and others are also known. The Fahrenheit temperature scale (in the second version adopted since 1714) has three fixed points: 0° corresponded to the temperature of a mixture of ice water and ammonia 96° – body temperature healthy person(under the arm or in the mouth). The reference temperature for comparing various thermometers was taken to be 32° for the melting point of the ice. The Fahrenheit scale is widely used in English speaking countries but it is almost never used in scientific literature. To convert Celsius temperature (°C) to Fahrenheit temperature (°F) there is a formula °F = (9/5)°C + 32 and for the reverse conversion there is a formula °C = (5/9)(°F-32) ). Both scales - both Fahrenheit and Celsius - are very inconvenient when conducting experiments in conditions where the temperature drops below the freezing point of water and is expressed as a negative number. For such cases, absolute temperature scales were introduced, which are based on extrapolation to the so-called absolute zero - the point at which molecular motion should stop. One of them is called the Rankine scale and the other is the absolute thermodynamic scale; temperatures are measured in degrees Rankine (°Ra) and kelvins (K). Both scales begin at absolute zero temperature and the freezing point of water corresponds to 491 7° R and 273 16 K. The number of degrees and kelvins between the freezing and boiling points of water on the Celsius scale and the absolute thermodynamic scale is the same and equal to 100; for the Fahrenheit and Rankine scales it is also the same but equal to 180. Celsius degrees are converted to kelvins using the formula K = °C + 273 16 and Fahrenheit degrees are converted to Rankine degrees using the formula °R = °F + 459 7. has been common in Europe for a long time Reaumur scale introduced in 1730 by Rene Antoine de Reaumur. It is not built arbitrarily like the Fahrenheit scale, but in accordance with the thermal expansion of alcohol (in a ratio of 1000:1080). 1 degree Reaumur is equal to 1/80 of the temperature interval between the points of melting ice (0°R) and boiling water (80°R) i.e. 1°R = 1.25°C 1°C = 0.8°R. but has now fallen into disuse.

Now all we need is snow, a cup, a thermometer and a little patience. Let's bring a cup of snow from the frost, put it in a warm, but not hot place, immerse a thermometer in the snow and watch the temperature. At first, the mercury column will creep upward relatively quickly. The snow remains dry. Having reached zero, the mercury column will stop. From this moment the snow begins to melt. Water appears at the bottom of the cup, but the thermometer still shows zero. By continuously stirring the snow, it is not difficult to make sure that until it all melts, the mercury will not budge.

What causes 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 collapses, the water temperature 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 change from solid to liquid. This amount, quite specific for each substance, is called the heat of fusion.

The heat of fusion is different for different substances. And it is here that when we begin to compare 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 is much greater than 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 requires 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 the heat of fusion 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 that we know how high the heat of fusion of ice is, we see that we have no reason to sometimes complain that ice melts “too quickly.” 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. It must be remembered that the ice cover alone occupies more than three percent of the entire earth's surface or 11 percent of all land. In the region of the south pole lies the huge continent of Antarctica, larger in size than Europe and Australia combined, covered with a continuous layer of ice. Permafrost reigns over millions of square kilometers of land. Glaciers and permafrost alone make up a fifth of the landmass. To this we must add the surface included in winter time snow. And then we can say that from one quarter to one third of the land is always covered with ice and snow. 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 the spring! After all, 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 sometimes copes with this work in several days. And it’s hard to imagine what kind of flood would await us if ice had, for example, the same heat of fusion as lead. All the snow could melt in one day or even in a few hours, and then the rivers, swollen to extraordinary sizes, would wash away both the most fertile layer of soil and plants from the surface of the earth, bringing untold disasters to all life on Earth.

Ice, when melting, absorbs a huge amount of heat. The same amount of heat is released by water when it freezes. If water had a small heat of fusion, then our rivers, lakes and seas would probably freeze after the first frost.

So, in addition to the high heat capacity of water, another remarkable feature has been added - a high heat of fusion.

On March 29, 1561, the Italian doctor Santorio was born - one of the inventors of the first mercury thermometer, a device that was an innovation for that time and which no person can do without today.

Santorio was not only a doctor, but also an anatomist and physiologist. He worked in Poland, Hungary and Croatia, actively studied the breathing process, “invisible evaporations” from the surface of the skin, and conducted research in the field of human metabolism. Santorio conducted experiments on himself and, studying the features human body, created many measuring instruments - a device for measuring the force of pulsation of arteries, scales for monitoring changes in a person’s mass, and the first mercury thermometer.

Three inventors

It is quite difficult to say today who exactly created the thermometer. The invention of the thermometer is attributed to many scientists at once - Galileo, Santorio, Lord Bacon, Robert Fludd, Scarpi, Cornelius Drebbel, Porte and Salomon de Caus. This is due to the fact that many scientists simultaneously worked on creating a device that would help measure the temperature of air, soil, water, and humans.

There is no description of this device in Galileo's own writings, but his students testified that in 1597 he created a thermoscope - an apparatus for raising water using heat. The thermoscope was a small glass ball with a glass tube soldered to it. The difference between a thermoscope and a modern thermometer is that in Galileo's invention, instead of mercury, air expanded. Also, it could only be used to judge the relative degree of heating or cooling of the body, since it did not yet have a scale.

Santorio from the University of Padua created his own device with which it was possible to measure temperature human body, but the device was so bulky that it was installed in the courtyard of the house. Santorio's invention had the shape of a ball and an oblong winding tube on which divisions were drawn; the free end of the tube was filled with tinted liquid. His invention dates back to 1626.

In 1657, Florentine scientists improved the Galileo thermoscope, in particular by equipping the device with a bead scale.

Later, scientists tried to improve the device, but all thermometers were air, and their readings depended not only on changes in body temperature, but also on atmospheric pressure.

The first liquid thermometers were described in 1667, but they burst if the water froze, so they began to use wine alcohol to create them. The invention of a thermometer, the data of which would not be determined by changes in atmospheric pressure, occurred thanks to the experiments of the physicist Evangelista Torricelli, a student of Galileo. As a result, the thermometer was filled with mercury, turned upside down, colored alcohol was added to the ball, and the upper end of the tube was sealed.

Single scale and mercury

For a long time, scientists could not find starting points, the distance between which could be divided evenly.

The points of thawing of ice and melted water were proposed as initial data for the scale. butter, the boiling point of water and some abstract concepts like “a significant degree of cold”.

A thermometer of a modern form, most suitable for household use, with an accurate measurement scale was created by the German physicist Gabriel Fahrenheit. He described his method for creating a thermometer in 1723. Initially, Fahrenheit created two alcohol thermometers, but then the physicist decided to use mercury in the thermometer. The Fahrenheit scale was based on three established points:

the first point was equal to zero degrees - this is the temperature of the composition of water, ice and ammonia;
the second, designated 32 degrees, is the temperature of the mixture of water and ice;
the third, the boiling point of water, was 212 degrees.
The scale was later named after its creator.

Reference
Today, the most common is the Celsius scale, the Fahrenheit scale is still used in the USA and England, and the Kelvin scale is used in scientific research.
But it was the Swedish astronomer, geologist and meteorologist Anders Celsius who finally established both constant points - melting ice and boiling water - in 1742. He divided the distance between points into 100 intervals, with the number 100 marking the melting point of ice, and 0 the boiling point of water.

Today, the Celsius scale is used inverted, that is, the melting point of ice is taken as 0°, and the boiling point of water as 100°.

According to one version, the scale was “turned over” by his contemporaries and compatriots, the botanist Carl Linnaeus and the astronomer Morten Stremer, after the death of Celsius, but according to another, Celsius himself turned over his scale on Stremer’s advice.

In 1848, the English physicist William Thomson (Lord Kelvin) proved the possibility of creating an absolute temperature scale, where the reference point is the value of absolute zero: -273.15 ° C - at this temperature further cooling of bodies is no longer possible.

Already in the middle of the 18th century, thermometers became a trade item, and they were made by artisans, but thermometers came into medicine much later, in the middle of the 19th century.

Modern thermometers

If in the 18th century there was a “boom” of discoveries in the field of temperature measurement systems, today work is increasingly being carried out to create methods for measuring temperature.

The scope of application of thermometers is extremely wide and is of particular importance for modern life person. A thermometer outside the window reports the temperature outside, a thermometer in the refrigerator helps control the quality of food storage, a thermometer in the oven allows you to maintain the temperature when baking, and a thermometer measures body temperature and helps assess the causes of poor health.
A thermometer is the most common type of thermometer, and it is the one that can be found in every home. However, mercury thermometers, which were once a brilliant discovery by scientists, are now gradually becoming a thing of the past as unsafe. Mercury thermometers contain 2 grams of mercury and have the highest accuracy in determining temperature, but you not only need to handle them correctly, but also know what to do if the thermometer suddenly breaks.
Mercury thermometers are being replaced by electronic or digital thermometers, which operate on the basis of a built-in metal sensor. There are also special thermal strips and infrared thermometers.

The question “What is a temperature scale?” - suitable for any physicist - from student to professor. A complete answer to this question would fill a whole book, and would serve as a good illustration of the changing views and progress of the physicist during the last four centuries.
Temperature is the degree of heating on a certain scale. You can use the sensitivity of your own skin to make a rough estimate without a thermometer, but our senses of heat and cold are limited and unreliable.

Experience. Skin sensitivity to heat and cold. This experience is very instructive. Place three bowls of water: one with very hot water, one with moderately warm water, and the third with very cold water. Place one hand in a hot basin and the other in a cold basin for 3 minutes. Then place both hands in a basin of warm water. Now ask each hand, what will it “tell” you about the temperature of the water?

The thermometer tells us exactly how much hotter or colder a thing is; with its help we can compare the degree of heating of different objects, using it again and again, we can compare observations made at different times. It is equipped with a certain constant, reproducible scale - a characteristic feature of any good instrument. The method of making a thermometer and the device itself dictate to us the scale and measurement system that we must use. The transition from rough sensations to an instrument with a scale is not just an improvement in our knitting. We invent and introduce a new concept - temperature.
Our crude idea of ​​hot and cold contains in embryo the concept of temperature. Research shows that when heated, many of the most important properties of things change, and... thermometers are needed to study these changes. The widespread use of thermometers in everyday life has relegated the meaning of the concept of temperature to the background. We think that a thermometer measures the temperature of our body, air or bath water, although in fact it only shows its own temperature. We consider temperature changes from 60 to 70° and from 40 to 50° to be the same. However, we apparently have no guarantee that they are really the same. We can only consider them the same by definition. Thermometers are still useful to us as faithful servants. But is Her Ladyship the Temperature really hidden behind their devoted “face” - the scale?

Simple thermometers and the Celsius scale
The temperature in thermometers is shown by a drop of liquid (mercury or colored alcohol) expanding when heated, placed in a tube with divisions. In order for the scale of one thermometer to coincide with another, we take two points: the melting of ice and the boiling of water under standard conditions and assign divisions of 0 and 100 to them, and divide the interval between them into 100 equal parts. So, if according to one thermometer the temperature of the water in the bath is 30°, then any other thermometer (if it is correctly calibrated) will show the same, even if it has a bubble and a tube of a completely different size. In the first thermometer, mercury expands by 30/100 the expansion from its melting point to its boiling point. It is reasonable to expect that in other thermometers the mercury will expand to the same extent and they will also show 30°. Here we rely on the Universality of Nature 2>.
Suppose now that we take another liquid, for example glycerin. Will this give the same scale at the same points? Of course, to harmonize with mercury, a glycerin thermometer must have 0° when ice melts and 100° when water boils. But will the thermometer readings be the same at intermediate temperatures? It turns out that when a mercury thermometer shows 50.0° C, a glycerin thermometer shows 47.6° C. Compared to a mercury thermometer, the glycerin thermometer lags a little behind in the first half of the way between the melting point of ice and the boiling point of water. (You can make thermometers that will give an even greater discrepancy. For example, a thermometer with water vapor would show 12° at a point where the mercury is 50°!

This produces the so-called Celsius scale, which is widely used today. In the USA, England and some other countries, the Fahrenheit scale is used, on which the melting points of ice and boiling water are marked with the numbers 32 and 212. Initially, the Fahrenheit scale was based on two other points. The temperature of the freezing mixture was taken as zero, and the number 96 (a number that can be divided into a large number of factors and therefore convenient to use) was compared normal temperature human body. After modification, when whole numbers were assigned to the standard points, the body temperature was between 98 and 99. A room temperature of 68° R corresponds to 20° C. Although the transition from one scale to another changes the numerical value of the temperature unit, it does not affect the concept itself temperature. The latest international agreement introduced another change: instead of the standard melting points of ice and boiling water defining the scale, the adoption of “absolute zero” and “triple point” for water was adopted. Although this change in the definition of temperature is fundamental, in the usual scientific work it makes virtually no difference. For the triple point, the number is chosen so that the new scale agrees very well with the old one.
2> This reasoning is somewhat naive. Glass also expands. Does the expansion of glass affect the height of the mercury column? For this reason, other than the simple expansion of mercury, what does the thermometer show? Let's say that two thermometers contain pure mercury, but their balls are made of different types of glass with different expansions. Will this affect the result?

3. Find the weight of the body P = ρgV

4. Determine the pressure exerted by the body on the horizontal surface P = , where F=P

Experimental work No. 12

Topic: “Study of the dependence of thermometer readings on external conditions».

Target: examine the dependence of the thermometer readings depending on external conditions: whether the sun’s rays fall on the thermometer or whether it is in the shade, what kind of substrate the thermometer is on, what color the screen covers the thermometer from the sun’s rays.

Tasks:

Educational: instilling accuracy, the ability to work in a team;

Equipment: table lamp, thermometer, sheets of white and black paper.

What is the air temperature in the room and outside? People are interested 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 “clarify” something like this: “And in the sun the thermometer went beyond 50°C!” Do such clarifications make sense? To answer this question, carry out the following experimental study and draw your own conclusions.

Progress:

Experiment 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. Take temperature measurements “in the sun” using first a dark, then a light substrate under the thermometer. To do this, place the thermometer on a sheet of white paper the first time, and on a sheet of black paper the second time. Record the thermometer readings.

Experiment 3. Take measurements “in the shadow”, blocking the light from the lamp with a sheet of white paper placed directly on the thermometer. Record the thermometer readings. Repeat the experiment, replacing white paper 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 outside?

A series of experiments with correct execution gives the following results.

Experiment 1 shows that the thermometer readings “in the sun” are noticeably higher than its readings “in the shade.” This fact must be explained as follows. 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 influence 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, exchanges heat with the surface of the table, and on the other hand, with the air. As a result, its temperature is higher than the air temperature, but lower than the table surface temperature. What then is the meaning of the thermometer readings “in the sun”?

A persistent lover of measuring air temperature “in the sun” can 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 they are precisely what interests 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 thermometer readings are significantly lower than on black paper, which absorbs light well and heats up more. Consequently, there is no clear answer to the question about the thermometer readings “in the sun”. The result will greatly depend on the color of the substrate under the thermometer, the color and structure of the surface of the thermometer balloon, and the presence or absence of wind.

The outdoor air temperature, when measured far from objects heated by solar radiation and excluding the direct influence of radiation on the thermometer, is the same “in the sun” and “in the shade”; it is simply the air temperature. But it should really only be measured “in the shadows.”

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 if the screen is located close to the thermometer, heating of the screen by solar radiation will lead to significant errors when measuring air temperature on a sunny day. The temperature increase will be especially large when the screen is dark, since such a screen absorbs almost all the energy of solar radiation incident on it, and much less when the screen is white, since such a screen reflects almost all the energy of solar radiation incident on it.

After doing this experimental research It is necessary to discuss a practically important question: how in practice should one measure the air temperature outside? 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 outdoor 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 bottle 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. Because White screen heats up less, the protective screen should be light, and it should be located at a sufficient distance from the thermometer.

A similar thing can be done to study the dependence of the readings of a room thermometer on its location. The result of execution homework there must be an 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 we need to exclude the influence of heated bodies and solar radiation on it. The thermometer should not be exposed to direct sunlight; the thermometer should not be placed near heating or lighting devices. You should not hang the thermometer on the outer wall of the room, which is high in summer and in winter. reduced temperature relative to the air temperature in the room.

Experimental work No. 13

Topic: “Determination of the percentage of snow in water.”

Target: Determine the percentage of snow in the water.

Tasks:

Educational: developing the ability to combine knowledge and practical skills;

Educational: development 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 equal to t=0.

2.Let's write the equation heat balance ad hoc:

m1 = cm3(t2-t1), where c is the specific heat capacity of water, is the specific heat of melting of ice, m1 is the mass of snow, m2 is the mass of water in the snow, m3 is the mass of poured water, t is the temperature of poured water.

Hence =

Required 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 the empty calorimeter, and then the calorimeter with a lump of wet snow. From 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 add enough warm water (mw) to the calorimeter with a lump of wet snow so that all the snow melts, having first measured the temperature of the warm water (to).

3. We weigh the calorimeter with water and melted snow and, based on the difference in weights, determine the mass of added warm water (mw).

4.Measure the final temperature (tocm) with a thermometer.

5. Let’s write down the heat balance equation:

cmв t = *(100 - x) + с(m+ mв) tocm.,

Where c is the specific heat capacity of water - 4200 J/kg , - specific heat of melting of snow

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: developing the ability to combine knowledge and practical skills;

Educational: instilling accuracy, the ability to work in a team;

Developmental: development of logical thinking, cognitive interest.

Equipment: thermometer, water, ice, graduated cylinder.

Progress:

1. Place a piece of ice in an empty container and pour enough water into it from the measuring cylinder until all the ice melts.

2. In this case, the heat balance equation will be written simply:

St1 (t1 - t2) = t2

where t2 is the mass of ice, tx is the mass of poured water, tx is the initial temperature of water, t2 is the final temperature of water equal to O °C, K is the specific heat of melting of ice. 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:

M = + m2 = ρадь, Vtot.

Since m2 = M - m1, then

Experimental work No. 15

Target: using the proposed equipment and a table of the dependence of saturated vapor pressure on temperature, determine the absolute and relative humidity in the room.

Tasks:

Educational: developing the ability to combine knowledge and practical skills;

Educational: instilling accuracy, the ability to work in a team;

Developmental: development of logical thinking, cognitive interest.

Equipment: glass, thermometer, ice, water.

Progress:

1.The easiest way to determine absolute air humidity is by the dew point. To measure the dew point, you must first measure the temperature t1 of the air. Then take a regular glass glass, 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 and ice and add a little from this vessel cold water into 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 dull due to the many small droplets of dew condensing on the glass. At this moment, you need to take the readings of the t2 thermometer.

3. Based on the value of temperature t2 - the dew point - the density ρ of saturated steam at temperature t2 can be determined from the table. It will be absolute humidity atmospheric air. Then you can find from the table the value of density r0 of saturated steam at temperature t1. From the found values ​​of the density r of saturated steam at temperature t2 and the density ρ0 of saturated steam at room temperature t1 is determined relative humidity air j.

Errors of measuring instruments

Density of liquids, metals and alloys, solids and materials.