I do not like the irony of Nekrasov analysis. "I do not like the irony of your ...": Analysis of the poem N.A.

What is couples and what is its basic properties.
Is it possible to count the air gas?
Are the laws of perfect gas for air applicable?

Water takes about 70.8% of the surface globe. Live organisms contain from 50 to 99.7% water. Figuratively speaking, living organisms are animated water. The atmosphere is about 13-15 thousand km3 water in the form of droplets, snow crystals and water vapor. Atmospheric water vapor affects the weather and the climate of the Earth.

Water vapor in the atmosphere.

Water steam in the air, despite the huge surfaces of the oceans, seas, lakes and rivers, is not always saturated. Moving air masses leads to the fact that in the places of our planet in this moment The evaporation of water prevails over condensation, and in others, on the contrary, condensation prevails. But in the air almost always there is some amount of water vapor.

Water vapor density in the air is called absolute humidity.

Absolute humidity is expressed, therefore, in kilograms per meter cubic (kg / m 3).

Partial pressure of water vapor

The atmospheric air is a mixture of various gases and water vapor. Each of the gases contributes to the total pressure produced by air to the body in it.

Pressure that would produce water vapor if all other gases were absent, called partial pressure of water vapor.

The partial pressure of the water vapor is taken for one of the indicators of air humidity. It is expressed in units of pressure - pasteers or millimeters of a mercury pillar.

Since the air is a mixture of gases, then the atmospheric pressure is determined by the sum of the partial pressures of all the components of dry air (oxygen, nitrogen, carbon dioxide, etc.) and water vapor.

Relative humidity.

According to partial pressure of water vapor and absolute humidity, it is also impossible to judge how much water vapor in these conditions is close to saturation. Namely, the intensity of the evaporation of water and the loss of moisture by living organisms depends. That is why the magnitude showing how much water vapor is close to saturation at this temperature - relative humidity.

Relative humidity Call the ratio of partial pressure P of water vapor contained in the air at a given temperature, to pressure r. n rich steam at the same temperature, expressed as a percentage:

Relative air humidity is usually less than 100%.

When decreasing temperature partial pressure Water vapors in the air can become equal pressure of a saturated pair. Steam begins to condense, and drops dew.

The temperature in which water vapor becomes saturated, called dew's point.

At the point of dew, you can determine the relative humidity.

Psychrometer.

Air humidity is measured using special devices. We will tell about one of them - psychrometer.

The psychrometer consists of two thermometers (Fig. 11.4). The reservoir of one of them remains dry, and it shows the air temperature. The reservoir of another is surrounded by a strip of fabric, the end of which is omitted into the water. Water evaporates, and thanks to this, the thermometer is cooled. The more relative humidity, the less intensively the evaporation and the temperature shown by the thermometer, surrounded by a damp cloth, closer to the temperature shown by the dry thermometer.

With a relative humidity equal to 100%, water will not evaporate and the readings of both thermometers will be the same. By the difference in the temperatures of these thermometers using special tables, air humidity can be determined.

The value of humidity.

The intensity of the evaporation of moisture from the surface of the skin of man depends on the humidity. And the evaporation of moisture has great importance To maintain the body temperature constant. IN spacecraft The most favorable relative air humidity (40-60%) is supported.

What do you think under what conditions the dew drops? Why in front of the rainy day in the evening there are no dew in the grass?

It is very important to know moisture in meteorology - due to weather prediction. Although the relative amount of water vapor in the atmosphere is relatively small (about 1%), its role in atmospheric phenomena is significant. The condensation of the water vapor leads to the formation of clouds and the subsequent fallout of precipitation. This highlights a large amount of heat. Conversely, the evaporation of water is accompanied by the absorption of heat.

In weaving, confectionery and other industries, a certain humidity is needed for normal flow.

It is very important to comply with the moisture regime in production in the manufacture of electronic circuits and instruments, in nanotechnology.

Storage of works of art and books requires maintenance of air humidity at the required level. With high humidity, the canvas on the walls can be saved, which will damage the colorful layer. Therefore, in museums on the walls you can see psychrometers.

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• provide assimilationconcepts humidity ;
• develop Independence of students; thinking; ability to draw conclusions; development of practical skills when working with physical equipment;
• showthe practical application and importance of this physical quantity.

Type of lesson: Lesson studying new material .

Equipment:

• for front work: a glass with water, a thermometer, a piece of gauze; Threads, psychrometric table.
• for demonstrations: Psychrometer, hair and condensation hygrometers, pear, alcohol.

During the classes

I. Repetition and checking homework

1. Word the definition of vaporization and condensation processes.

2. What types of vaporization do you know? What do they differ from each other?

3. What should the fluid evaporate occur?

4. Speed \u200b\u200bevaporation depends on any focus?

5. What is the dedication of vaporization?

6. What is the resulting amount of heat during vaporization?

7. Why is Hisrezhar postponed easier?

8. Is the internal energy of 1 kg of water and steam at a temperature of 100 ° C

9. Why water in a bottle, tightly closed plug, does not evaporate?

II. Studying new material

Water steam in the air, despite the huge surfaces of rivers, lakes, the ocean is saturated, the atmosphere is an open vessel. The movement of the air masses leads to the fact that in some places, the evaporation of water prevails over condensation, and in others, on the contrary.

The atmospheric air is a mixture of various gases and water vapor.

Pressure that would produce water vapor if all the others are gasesotsed, called partial pressure (or elasticity) water vapor.

The water vapor density contained in the air can be taken for air humidity. This magnitude is called absolute humidity [g / m 3].

Knowledge of partial pressure of water vapor or absolute humidity say nothing to the water vapor is far from saturation.

To do this, enter the magnitude showing how much water steam at this temperature is close to saturation - relative humidity.

Relative humidity call the ratio of absolute humidity to the density of 0 saturated water vapor at the same temperature expressed as a percentage.

P - partial pressure at a given temperature;

P 0 - the pressure of saturated steam at the same temperature;

Absolute humidity;

0 is the density of saturated water vapor at a given temperature.

The pressure and density of the saturated pair at different temperatures can be found using special tables.

When the wet air is cooled at constant pressure, its relative humidity increases, the lower the temperature, the closer the partial pressure of steam in the air to the pressure of saturated steam.

Temperature t, to which the air should cool so that the steam in it reached the saturation state (with this humidity, air and constant pressure), is called dew point.

Pressure of saturated water vapor at an air temperature dew point There is a partial pressure of the water vapor contained in the atmosphere. When cooling the air to the dew point begins the condensation of vapors : fog appears, falls out dew.The dew point also characterizes the humidity.

Air humidity can be determined by special devices.

1. Condensation hygrometer

With it, they determine the dew point. This is the most accurate way to change relative humidity.

2. Hair hygrometer

Its effect on the properties of the human will fromand lengthened with increasing relative humidity.

Applied in cases where the collaboration of air humidity is not required of great accuracy.

3. Psychrometer

Usually enjoy in cases where a fairly accurate and rapid determination of air humidity is required.

Air humidity value for living organisms

At a temperature of 20-25 ° with the most favorable person, air with a relative humidity from 40% to 60% is considered to be air. When the environment has a temperature higher than the body temperature of a person, then a strengthened sweating occurs. Abundant selection of sweat leads to the cooling of the body. However, such a sweating is a significant burden for a person.

The relative humidity is below 40% at normal air temperature is also harmful, as it leads to enhanced loss of moisture of organisms, which leads to its dehydration. Especially low humidity indoor air in winter; It is 10-20%. With low air humidity occurs fast evaporation Moisture from the surface and drying of the mucous membrane of the nose, larynx, lungs, which can lead to deterioration of well-being. Also at low air humidity in external environment Pathogenic microorganisms remain longer, and more static charge accumulates on the surface of the items. Therefore, in the winter time, moisturizing with porous humidifiers produce in residential premises. Good humidifiers are plants.

If the relative humidity is high, then we say that the air wet and suffocating. High humidity is in oppressing, since evaporation occurs very slowly. The concentration of water vapors in the air in this case is high, as a result of which the air molecules return to the liquid almost as quickly as evaporated. If the sweat from the body evaporates slowly, then the body is cooled very weak, and we feel not entirely comfortable. With a relative humidity of 100%, the evaporation cannot occur at all - under such conditions, wet clothing or wet skin will never be dried.

From the course of biology, you know about the various fixtures of plants in arid areas. But plants are adapted to high humidity. So, Motherland Monster - the wet Monster Equatorial Forest with a relative humidity close to 100%, "crying", it removes excess moisture through the holes in the leaves - the guides. In modern buildings, air conditioning is available and maintaining air conditioning in closed rooms, the most profitable to the well-being of people. This automatically regulates temperature, humidity, air composition.

Exceptional importance for the formation of frost has air humidity. If the humidity is large and the air is close to the saturation of pairs, then when the temperature decreases, the air may become rich and starts to fall out. But when the water vapor is condensation, the energy (the specific heat of the vaporization at a temperature close to 0 ° C is 2490 kJ / kg), Therefore, the air at the surface of the soil during the formation of the dew will not be cooled below the dew point and the probability of frost occurs will decrease. The probability of freezing depends on the first, from the speed of lowering the temperature and,

Secondly, from air humidity. It is enough to know one of these data to more or less accurately predict the likelihood of freezing.

Questions for repetition:

1. What is understood under the humidity of the air?
2. What is called absolute humidity? What formula expresses the meaning of this concept? In which units of it express?
3. What is the elasticity of water vapor?
4. What is called relative humidity? What formulas express the meaning of this concept in physics and meteorology? In which units of it express?
5. Relative air humidity 70%, what does this mean?
6. What do they call the dew point?

With which devices are the air humidity determine? What are the subjective sensations of air humidity by man? Having drawn drawing, explain the device and the principle of operation of the hair and condensation hygrometer and psychrometer.

Laboratory work №4 "Measurement of relative humidity"

Purpose: learn how to determine the relative humidity of the air, develop practical skills when working with physical equipment.

Equipment: Thermometer, Gauze Bandage, Water, Psychometric Table

During the classes

Before performing the work, it is necessary to draw the attention of students not only to the content and course of work, but also on the rules for circulation of thermometers and glass vessels. It is necessary to remind you that all the time, while the thermometer is not used for measurements, it must be in the case. When measuring the temperature, the thermometer should be kept behind the top edge. This will determine the temperature with the greatest accuracy.

The first temperature measurements should be carried out with a dry thermometer. This temperature in the audience will not change during operation.

To measure the temperature, a wet thermometer is better to take a piece of gauze as a tissue. Marley absorbs very well and moves water from the wet edge to dry.

Using a psychrometric table, it is easy to determine the value of relative humidity.

Let be t C \u003d H\u003d 22 ° С, t M \u003d T 2\u003d 19 ° С. Then t \u003d t c- 1 w \u003d3 ° C.

On the table we find relative humidity. In this case, it is 76%.

For comparison, you can measure the relative humidity of the air outside. For this, a group of two or three students who successfully coped with the main part of the work can be asked to carry out similar dimensions on the street. This should take no more than 5 minutes. The resulting value of humidity can be compared with the humidity in the class.

The results of the work are summarized in conclusions. They should noted not only the formal values \u200b\u200bof the final results, but also indicate the reasons that lead to the errors.

III. Solving tasks

Since this laboratory work Such a simple content and is small in volume, the remaining part of the lesson can be devoted to solving the tasks on the topic under study. To solve problems, it is not necessary for all students to solve them at the same time. As the work performed, they can receive tasks individually.

You can offer the following simple tasks:

On the street there is a cold autumn rain. In which case, the lingerie will dry faster, awesome in the kitchen: when is the fortune point open, or when is closed? Why?

Air humidity is 78%, and the reading of the dry thermometer is 12 ° C. What temperature shows a wet thermometer? (Answer:10 ° C.)

The difference in the readings of dry and wet thermometers is equal to 4 ° C. Relative air humidity 60%. What are the testimony of a dry and wet thermometer? (Answer: T C -L9° С t M.\u003d 10 ° C.)

Homework

• Repeat paragraph 17 textbook.
• Task number 3. p. 43.

Messages of students on the role of evaporation in the life of plants and animals.

Evaporation in the life of plants

For the normal existence of the plant cell requires its saturation with water. For algae, it is a natural consequence of the conditions of their existence, sushi plants are achieved as a result of two opposite processes: water absorption roots and evaporation. For successful photosynthesis of chlo-! Rophillonal cells of land plants must maintain the closest contact with the surrounding atmosphere, which supplies them necessary for them with carbon dioxide gas; However, this close contact inevitably leads to the fact that the saturating cells water continuously evaporates into the surrounding space, and the same solar energy that delivers the plant necessary for photosynthesis, absorbing chlorophyll, contributes to the heating of the sheet, and thus enhance the evaporation process.

Very few, and moreover, low-organized, plants, nimeximer MAs and lichens, can withstand long interruptions in water supply and transfer this time in a state of complete yyankiy. From higher plants, only some representatives of the rock and desert flora are capable of this, such as the Oskow, common in the sands of the doodles. For the enormous majority of W. King Plants, such a drying would be mortally, and therefore, they are approximately equal to its coming.

To imagine the scale of water evaporation by plants, we give such an example: in one growing season, one blooming of sunflower or corn evaporates to 200 kg and more water, i.e. solid sizes barrel! With this energetic flow, no less energetic production is required. To do this (Mud root system, the sizes of which are huge scores of the number of roots and root hairs for winter rye gave the following amazing numbers: the roots turned out to be almost four minutes to make millions, the total length of all the roots of 600 km, and their total top is about 225 m 2. On these roots there were about 15 billion root hairs with total area in 400 m 2.

The amount of water consumed by the plant during its lives is largely depends on the climate. In the hot dry climate, the plants consume no less, and sometimes even more in dy, than in the climate more wet, these plants are more developed root system and less development has a sheet surface. The flooding plants of raw, shady tropic forests, shores of reservoirs are consumed the least: they have thin wide leaves, weak root and conductive systems. In the plants of dry locally, where water in the soil is very small, and the air is hot and dry, a variety of techniques are observed to these harsh conditions. Interesting plants desert. This, for example, cacti plants with thick fleshy trunks, the leaves of which turned into spines. They have a minor surface with a large volume, thick covers, few permeable for water and water vapor, with a few, almost always closed astians. Therefore, even in a strong heat, cacti evaporates little water.

Other plants are desert zones (camel spines, steppe alfalfa, wormwoods) Thin leaves with wide open dusts, which are vigorously assimilated and evaporate, due to which the temperature of the leaves is significantly reduced. Often, the leaves are covered with a thick layer of gray or white hairs, representing a translucent screen that protects plants from overheating and reduces the intensity of evaporation.

Many desert plants (nick, rolling-field, heather) have hard, leathery leaves. Such plants are capable of transfering a long building. At this time, their leaves are twisted into the tube, and the stomaps are inside it.

The evaporation conditions in the winter change dramatically. From the frozen soil roots can not suck water. Therefore, due to the leaf fall, the evaporation of moisture is reduced by the plant. In addition, in the absence of leaves, less snow is delayed on the crown, which protects plants from mechanical damage.

The role of evaporation processes for animal organisms

Evaporation is the most easily adjustable method of smallerizing internal energy. All conditions implanting complaints are disturbed by the regulation of the organism heat transfer. So, the elaper, rubber, adhesive, synthetic clothing makes it difficult to cheer the body temperature.

For the thermoregulation of the body, the Poto-Eagle plays an important role, it ensures the constancy of the body temperature of whether the animal. Due to the evaporation of the sweat, internal irregular decreases, due to this the body is cooled.

Normal person is considered air with a relative humidity of 40 to 60%. When the environment has a temperature higher than a person's body, then it is reinforced. Abundant swelling leads to cooling the body, helps to work in high temperature conditions. However, such an active sweating is a significant load for a person! If yet the absolute moisture is high, it is still harder to live and work (wet tropics, some shops, such as dyeing).

The relative humidity is below 40% at normal air temperature is also harmful, as it leads to enhanced loss of moisture by the body, which leads to its dehydration.

Very interesting from the point of view of thermoregulation and the role of evaporation processes, some living beings. It is known, for example, that a camel can not drink two weeks. This is explained by the fact that it is very economically spending water. The camel almost does not sweat even to the forty-portus heat. His body is covered with thick and dense wool - wool saves from overheating (on the back of a camel in a sultry noon she is heated to eighty degrees, and the skin under it is to forty!). Wool prevents both the evaporation of moisture from the body (at a cut-off camel, the sweating increases by 50%). Camel Never, even the strongest heat, does not reveal the mouth: because with the mucous membrane of the oral cavity, if you open the widespread mouth, evaporate a lot of water! Camel breathing frequency is very low -8 times a minute. Thereby less water It leaves the body with air. In the heat, however, the frequency of breathing increases to 16 times per minute. (Compare: Byk under the same conditions breathe 250, and the dog is 300-400 times per minute.) In addition, the body temperature of the camel drops at night to 34 °, and in the afternoon, in the heat, rises to 40-41 °. It is very important for water saving. The camel has a very curious device for conserving the water of the future it is known that out of fat, when he "burns" in the body, it turns out a lot of water - 107 g out of 100 g of fat. Thus, from their hubbles, a camel can, if necessary, can be removed to half antenna.

From the point of view of savings in water spending even more amazing American carcass jumpers (kangaroic rats). They never drink. Kangaroic rats live and the desert of Arizona and nibble seeds and dry herbs. Almost all the water, which is available in their body, endogenous, i.e. It turns out in cells when digesting food. Experiments have shown that from 100 g of pearl crook, which was fed by Kangarochi rats, they received, digest and oxidized it, 54 g of water!

In the thermal regulation of birds, air bags play a major role. In the hot time from the inner surface of the air mesh, moisture evaporates, which contributes to the cooling of the body. II links with this bird in hot weather opens the beak. (Katz //./\u003e Biophysics in physics lessons. - M.: Enlightenment, 1974).

n. independent work

What the amount of heat is highlighted by Mreyfull combustion of 20 kg of stone coal? (Answer:418 MJ)

What amount of heat is highlighted with complete combustion of 50 liters of methane? Methane density Please note 0.7 kg / m 3. (Answer: -1.7MJ)

On a cup with yogurt, it is written: the energy value of 72 kcal. Express the energy value of the product in J.

The heat of the combustion of the daily diet for schoolchildren of your age is about 1.2 MJ.

1) whether consumption is enough for you for 100 g of fat curd, 50 g of wheat bread, 50 g of beef and 200 g potatoes. Required additional data:

• cottage cheese 9755;
• wheat bread 9261;
• beef 7524;
• potatoes 3776.

2) whether consumption is enough for you during the day 100 g of perch, 50 g of fresh cucumbers, 200 g of grapes, 100 g of rye bread, 20 g of sunflower oil and 150 g of cream ice cream.

Specific heat combustion Q x 10 3, J / kg:

• perch 3520;
• fresh cucumbers 572;
• grapes 2400;
• rye bread 8884;
• sunflower oil 38900;
• ice cream cream 7498.,

(Answer: 1) consumed about 2.2 MJ - enough; 2) Consued to3.7 MJ - enough.)

When preparing for lessons within two hours you spend about 800 kJ of energy. Do you restore the stock of energy if you drink 200 ml of skimmed milk and eat 50 g of wheat bread? The density of low fat milk is equal to 1036 kg / m 3. (Answer:Consucted about 1 MJ - enough.)

Water from the menzurka was overflowed into the vessel heated by the flame of the alcohol, and evaporated. Calculate the mass of burnt alcohol. Heating the vessel and losses for air heating can be neglected. (Answer:1.26)

• What amount of heat is highlighted with complete combustion of 1 tons of anthracite? (Answer:26.8. 109 J.)
• What kind of biogas weight should be burned to be distinguished 50 MJ heat? (Answer: 2.kg.)
• What amount of heat is highlighted during the combustion of 5 liters of fuel oil. Raft nostamazuta Take 890 kg / m 3. (Answer:about 173 MJ.)

On a candy box, it is written: caloric content of 100 g 580 kcal. Express the nicerity of the product in J.

Examine labels of different food products. Write down the energy I, S.kuyu value (caloric content) of products, expressing it in Joules or Ka-Yurii (kilocalories).

When riding a bike in 1 hour you spend about 2,260,000 J. Schchergia. Do you restore the reserve of energy if you eat 200 g cherries?

You will need

• - mercury thermometer;
• - Sealed vessel;
• - table of dependence of saturated water vapor on temperature;
• - Psychrometer.

Instruction

For direct measurement Humidity, telect air sample into a sealed vessel and start cooling it. When the vessel determined on the walls, dew (steam condensed) will appear, write down the temperature value at which it happens. By specifically, find the table of saturated steam at that temperature that it condensed. This will be the absolute humidity of the air whose sample was selected.

Take two thermometers. One of them wrap with a damp cloth, moisturize it as you dry or lower this thermometer into a cup with water.

Watch the instrument readings - the values \u200b\u200bof the wet thermometer will be below dry. Next, use a special table.

Write down or remember the readings of both thermometers, count the difference, find the options received in the table. The designation of the relative humidity of the air will be at the intersection of indicators.

Purchase a special device that "psychrometer". Its action is based on the testimony of two thermometers, and in the composition there is a complete one. There are several types of psychrometer - station, remote and aspiration. Stationary are strengthened in a special meteorological booth on a tripod, and the accuracy of the readings of such an appliance depends on the speed of air flows inside the booth.

Aspiration psychrometer consists of two thermometers, tables and a fan, which provides a constant air flow rate. Thermometers are fixed in a special frame that protects them from exposure to direct sunlight.

The remote psychrometer uses thermocouples, resistance thermometers, thermistors. The device has a complex design and requires constant supply of distilled water, but is characterized by a smaller error.

Learn air humidity using a hygrometer. This measuring device happens different types - weight, hair, film. The effect of each of them is based on various principles. You can learn about the action of the device in detail in the store - ask the instructions or receive advice from the seller.

Video on the topic

Helpful advice

The most comfortable values \u200b\u200bfor a person - 40-60%. Air humidity indoors can be improved or lowering artificially. Put the tanks with water at low indicators, and at high - turn on the heating devices.

Sources:

• Psychriculture Table, temperature and humidity, atmospheric pressure

There is always some amount of water vapor in the air. At the same time distinguish absolute and relative humidity. The first is the density of water vapor in the air at a certain temperature. BUT B. everyday life This indicator does not represent much interest. It is quite another thing - relative humidity.

Weight, or rather the mass, water vapor contained in 1 m3 of air, is called absolute humidity. In other words, it is water vapor density in the air. At the same temperature, the air can absorb a completely defined amount of water vapor and to achieve the state of complete saturation. In the state of its saturation wears the name moisture complex.

The magnitude of air moisture capacity increases sharply with an increase in its temperature. The ratio of magnitude absolute humidity of air At a given temperature, the magnitude of its moisture complex at the same temperature is called relative humidity.

To determine the temperature and relative humidity Use a special instrument - a psychrometer. The psychrometer consists of two thermometers. The ball of one of them is moistened with a gauze cover, the end of which is lowered into a vessel with water. Another thermometer remains dry and shows the ambient temperature. The moistened thermometer shows the temperature lower than dry, as moisture from gauze requires a certain heat consumption. The temperature of the moistened thermometer is called cooling limit. The difference between the testimony of dry and moistened thermometers is called polyometric difference.

There is a certain dependence between the magnitude of the psychrometric difference and relative. The greater the psychrometric difference at this air temperature, the less the relative humidity of the air and the more moisture can absorb air. With a difference equal to zero air saturated and further evaporation of moisture in so air not happening.

Absolute humidity

(f) - This is the amount of water vapor actually contained in 1m 3 air:
f. \u003d M (mass of water vapor contained in the air) / V (volume)
Usually used as an absolute humidity unit: (f) \u003d g / m 3

Relative humidity

Relative humidity: φ \u003d (absolute humidity) / (maximum humidity)
Relative humidity is usually expressed as a percentage. These values \u200b\u200bare related to the following relationship:
φ \u003d (F × 100) / FMAX

What is a dew point