accompanied by the transfer of matter? A. Thermal conductivity. B. Radiation. B. Convection. 3. Which of the following substances has the highest thermal conductivity?A. Fur. B. Tree. B. Steel. 4. Which of the following substances has the lowest thermal conductivity? A. Sawdust. B. Lead. B. Copper.5. Name a possible method of heat transfer between bodies separated by airless space. A. Thermal conductivity. B. Convection. B. Radiation. 6. A metal handle and a wooden door will feel equally warm to the touch at a temperature...A.above body temperature.B. below body temperature. B. equal to body temperature. 7. What happens to the body temperature if it absorbs as much energy as it emits? A. The body heats up. B. The body cools down.B. Body temperature does not change.8. In what way does heat transfer occur in liquids? A. Thermal conductivity. B. Convection. B. Radiation.9. Which of the following substances has the least A. Air. B. Cast iron. B. Aluminum10. The specific heat capacity of water is 4200 (J/kg*0С). This means that...A.to heat water weighing 4200 kg by 1 °C, an amount of heat equal to 1 J.B. is required. to heat water weighing 1 kg by 4200 ° C, an amount of heat equal to 1 J.B is required. To heat water weighing 1 kg by 1 ° C, it requires 11. The specific heat of combustion of a fuel shows how much coA. combustion of the fuel is. B. complete combustion of fuel.B. with complete combustion of fuel weighing 1 kg.12. Evaporation occurs...A.at any temperature.B. at boiling point. B. at a specific temperature for each liquid.13. In the presence of wind, evaporation occurs...A.faster.B. slower.B. at the same speed as in its absence.14. Can the efficiency of a heat engine become 100% if friction between the moving parts of this machine is reduced to zero?A. Yes. B. No.15. From which pole of the magnet do the magnetic field lines emerge?A. From the north. B. From the south. B. From both poles.16. A body charged with a negative charge is brought to the ball of an uncharged electroscope without touching it. What charge will the leaves of the electroscope acquire? A. Negative. B. Positive. B. None.17. Can an atom of hydrogen or any other substance change its charge by 1.5 times the charge of an electron?A. Yes. B. No.18. What image is produced on the human retina?A. Magnified, real, inverted.B. Diminished, real, inverted.V. Enlarged, imaginary, direct.G. Diminished, imaginary, direct.19. What does an ammeter measure?A) Electrical resistance of conductorsB) Voltage at the poles of a current source or at some section of the circuitC) Current strength in the circuitD) Electric current power20. Diffusion is: A) The process of increasing temperature B) The phenomenon in which mutual penetration of molecules of one substance occurs between the molecules of another C) The phenomenon in which a body passes from a solid state to a liquid state D) The process of increasing the density of a body 21. Efficiency formula:A) ŋ= Аn* 100%АɜB) ŋ= Аɜ * 100%АnВ) ŋ= Аn * Аɜ100%D) ŋ= Аn * Аɜ * 100%22. What does Archimedes' law say?A) The buoyancy force acting on a body immersed in a liquid is equal to the weight of the liquid displaced by this bodyB) The buoyancy force acting on a body immersed in a liquid is equal to the speed of immersion of this body in the liquidC) The buoyancy force acting on a body immersed in a liquid , is equal to the density of this body D) The buoyant force acting on a body immersed in a liquid is equal to the weight of this body23. What deyA)tep24. InnerA) only B) only C) only D) from topics25. Which of the following substances are conductors? a) rubber; b) copper, c) plastic; d) glass.26. The body is electrified only when it...... charge.a) acquires; b) loses; c) gains or loses.27. Which of the following substances are dielectrics? a) rubber; b) copper; c) sulfuric acid solution; d) steel.28. Likely charged bodies ......., and oppositely charged ones - ......a) ...repel, ...attract, b) ...attract, ...repel.29. Electric current is called...A. Movement of electrons along a conductor.B. Ordered movement of electrons along a conductor.V. Ordered movement of protons along a conductor.G. Ordered movement of charged particles.D. Movement of electric charges along a conductor.30. What energy transformation occurs when an electric coffee grinder operates? Electrical energy is converted...A. To the chemical department. B. To mechanical. B. Into the light room. G. Internal
Option I Convection is a type of heat transfer in which energy... A. Is transferred from a heated body using rays.B. It is transferred from the heated end of the body to the cold one, but the substance itself does not move.
B. Transported by the particles of the substance themselves.
2. What is the method of heat transfer from a fire?
A. Radiation.
B. Thermal conductivity.
B. Convection.
3. A spoon placed in a glass of hot water heats up. How does heat transfer occur?
A. Radiation.
B. Thermal conductivity.
B. Convection.
4. How does heat transfer occur when car tires heat up during braking?
A. Convection.
B. Thermal conductivity.
B. Radiation.
G. Work.
5. Which substance has the greatest thermal conductivity?
A. Wool.
B. Iron.
B. Paper.
Option 2
1. The type of heat transfer in which energy from a heated body is transferred to a cold body using rays is called...
A. Radiation.
B. Convection.
B. Thermal conductivity.
2. What is the heat transfer method of water heating?
A. Radiation.
B. Thermal conductivity.
B. Convection.
3. By what method of heat transfer does the Sun heat the Earth?
A. Thermal conductivity.
B. Convection.
B. Radiation.
4. What is the method of transferring energy from a hot iron to fabric?
A. Work.
B. Thermal conductivity.
B. Convection.
D. Radiation.
5. Will the temperature of a body change if it absorbs more energy than it emits?
A. The body will heat up.
B. Body temperature will not change.
B. The body will cool down.
Travelers warm themselves in the harsh winterby the fire. Which type of heat transfer plays
main role in the transfer of heat from the fire to
to a person? Suggest a way to delay
heat from the fire. This method is well known
people who learn physics from nature. On
in the north they wear fur hats to protect themselves from
cold, and in the south - from the heat. Explain
the feasibility of this.
on topic "Types of heat transfer."
I-option.
№ 1. Which method of heat transfer is the heating of solids based on?
№ 2. What type of heat transfer is accompanied by the transfer of matter?
A. Thermal conductivity. B. Convection. B. Radiation.
№ 3. Which of the following substances has the highest thermal conductivity?
A. Fur. B. Tree. V. Steel.
№ 4. Which of the following substances has the lowest thermal conductivity?
A. Sawdust. B. Lead. B. Copper.
№ 5. In which pan will the liquid in it cool faster?
A. 1.
B. 2.
B. The liquid will cool faster if you put
ice on the side.
№ 6. Name a possible method of heat transfer between bodies separated by an airless
space.
A. Thermal conductivity. B. Convection. B. Radiation.
8th grade. Independent work
on topic "Types of heat transfer."
Option II.
№ 1. In what way does heat transfer occur in liquids?
A. Thermal conductivity. B. Convection. B. Radiation.
№ 2. What types of heat transfer are not accompanied by the transfer of matter?
A. Convection and thermal conductivity. B. Radiation and convection. B. Thermal conductivity and radiation.
№ 3. Which of the following substances has the lowest thermal conductivity?
A. Air. B. Cast iron. B. Aluminum.
№ 4. Which of the following substances has good thermal conductivity?
A. Straw. B. Cotton wool. B. Iron.
№ 5. In which kettle will boiling water cool faster?
A. 1.
B. 2.
№ 6. In what cases can heat transfer occur by convection?
A. In the sand. B. In the air. V. In the stone.
№ 7. A metal handle will feel colder to the touch than a wooden door at temperatures...
№ 7. The metal handle and the wooden door will feel equally warm to the touch when
temperature...
A. above body temperature. B. below body temperature. B. equal to body temperature.
№ 8. In what direction does air move in the atmosphere on a hot summer day (see figure)?
A. ABCD .
B. ADCB .
№ 9. What happens to a body’s temperature if it absorbs as much energy as it emits?
№ 10. Which glass is more likely to remain intact when pouring boiling water?
A. 1.
B. 2.
№ 8. The upper part of the test tube with ice was placed in the flame. Will the ice melt at the bottom?
test tubes?
A. It will melt.
B. Will not melt.
№ 9. What happens to a body’s temperature if it absorbs more energy than it emits?
A. The body heats up. B. The body cools. B. Body temperature does not change.
№ 10. When comparing the thermal conductivity of metals, copper and steel were chosen for the experiment
rods to which buttons are attached with plasticine. Which rod has more
thermal conductivity?
A. Steel.
B. Copper.
8th grade. Independent work
on topic "Types of heat transfer."
ANSWERS
1
2
3
4
5
6
7
8
9
10
I-option
Option II
Any 7 tasks – “3”
Any 8 tasks – “4”
Any 9 tasks – “5”
, course mechanics.docx, 71310_zadanie_Technical mechanics (Machine parts) TM DKR 16 year, Theoretical mechanics.docx, 020804 Course of lectures Mechanics Physics 2009.pdf, applied mechanics.docx, Applied mechanics (theor_mech_) (2523).pdf.
11. What type of heat transfer is not accompanied by the transfer of matter?
convection only;
thermal conductivity only;
radiation only
12. What is thermal motion called?
ordered movement of a large number of molecules;
continuous random movement of a large number of molecules;
rectilinear movement of an individual molecule.
17. Which of the following is the definition of internal energy?
the energy possessed by a body due to its motion;
energy, which is determined by the position of interacting bodies or parts of the same body;
the energy of movement and interaction of the particles that make up the body.
13. What physical quantities does the internal energy of a body depend on?
on height above the ground and speed;
on temperature and body weight.
14. In what state of matter does convection proceed faster (under the same conditions)?
in liquid;
in solid;
in gaseous
15. What kind of motion of molecules and atoms in the solid state is called thermal?
random movement of particles in all sorts of directions at different speeds;
random movement of particles in all possible directions with the same speeds at the same temperature;
ordered movement of particles with a speed proportional to temperature;
oscillatory movement of particles in different directions around certain equilibrium positions.
16. In which of the listed cases is energy transferred to the body mainly by thermal conductivity?
a person warming himself by the fire;
from a hot iron to ironed linen;
a person warming up by running.
17. The basis of the structure of biological membranes is:
layer of proteins;
carbohydrates;
double layer of phospholipids;
amino acids;
DNA double helix.
18. For the occurrence of a transmembrane potential difference it is necessary and sufficient:
the presence of selective membrane permeability;
difference in ion concentrations on both sides of the membrane;
the presence of selective permeability and differences in ion concentrations on both sides of the membrane;
the emergence of autowave processes;
increased permeability to ions.
19. Active transport of ions is carried out by. . .
energy of hydrolysis of high-energy bonds of ATP;
processes of ion diffusion through membranes;
transfer of ions through the membrane with the participation of carrier molecules;
lateral diffusion of molecules in the membrane;
electrodiffusion of ions.
20. Nernst's equation for the rest potential shows that. . .
the resting potential arises as a result of active transport;
the transfer of ions is determined by the unevenness of their distribution (concentration gradient) and the influence of the electric field (electric potential gradient);
the main role in the occurrence of the resting potential belongs to potassium ions;
membranes have selective permeability;
the permeability coefficient of substances through the membrane is determined by their mobility.
21. Provided that the membrane is permeable only to potassium ions, the Goldman-Hodgkin-Katz equation is transformed into the equation. . .
Nernst for potassium ions;
Nernst for sodium ions;
Fika for diffusion of potassium ions.
.What transmembrane redistribution of K⁺ and Na⁺ ions is characteristic of the initial moment of development of the action potential?
active penetration of K⁺ ions into the cell;
active penetration of Na⁺ ions into the cell;
active release of K⁺ ions from the cell;
active release of Na⁺ ions from the cell.
.What is the sign of the potential difference between the inner and outer surfaces of cell membranes at rest?
positive;
negative;
the potential difference is zero.
1. convection only;
2. thermal conductivity only;
3. radiation only
What is thermal motion?
1. ordered movement of a large number of molecules;
2. continuous random movement of a large number of molecules;
3. rectilinear movement of an individual molecule.
17. Which of the following is the definition of internal energy?
1. the energy that a body possesses due to its movement;
2. energy, which is determined by the position of interacting bodies or parts of the same body;
3. the energy of movement and interaction of particles that make up the body.
What physical quantities does the internal energy of a body depend on?
1. on the mass and speed of the body;
2. on height above the ground and speed;
3. on temperature and body weight.
In what state of matter does convection proceed faster (under the same conditions)?
1. in liquid;
2. in solid;
3. in gaseous form.
What kind of motion of molecules and atoms in the solid state is called thermal?
1. random movement of particles in all possible directions at different speeds;
2. random movement of particles in all possible directions with the same speeds at the same temperature;
3. ordered movement of particles with a speed proportional to temperature;
4. oscillatory movement of particles in different directions around certain equilibrium positions.
In which of the following cases is energy transferred to the body mainly by thermal conductivity?
1. from the heated Earth by the upper layer of the atmosphere;
2. a person warming himself by the fire;
3. from a hot iron to ironed linen;
4. a person warming up by running.
17. The basis of the structure of biological membranes is:
1. layer of proteins;
2. carbohydrates;
3. double layer of phospholipids;
4. amino acids;
5. DNA double helix.
18. For the occurrence of a transmembrane potential difference it is necessary and sufficient:
1. the presence of selective membrane permeability;
2. difference in ion concentrations on both sides of the membrane;
3. the presence of selective permeability and differences in ion concentrations on both sides of the membrane;
4. emergence of autowave processes;
5. increased permeability for ions.
Active transport of ions is carried out due to. . .
1. energy of hydrolysis of high-energy bonds of ATP;
2. processes of ion diffusion through membranes;
3. transfer of ions through the membrane with the participation of carrier molecules;
4. lateral diffusion of molecules in the membrane;
5. electrodiffusion of ions.
Nernst's equation for the resting potential shows that. . .
1. resting potential arises as a result of active transport;
2. the transfer of ions is determined by the unevenness of their distribution (concentration gradient) and the influence of the electric field (electric potential gradient);
3. the main role in the occurrence of the resting potential belongs to potassium ions;
4. membranes have selective permeability;
5. The coefficient of permeability of substances through the membrane is determined by their mobility.
Provided that the membrane is permeable only to potassium ions, the Goldman-Hodgkin-Katz equation is transformed into the equation. . .
1. Nernst for potassium ions;
2. Nernst for sodium ions;
3. Fika for diffusion of potassium ions.
22.What transmembrane redistribution of K⁺ and Na⁺ ions is characteristic of the initial moment of development of the action potential?
1. active penetration of K⁺ ions into the cell;
2. active penetration of Na⁺ ions into the cell;
3. active release of K⁺ ions from the cell;
4. active release of Na⁺ ions from the cell.
What is the sign of the potential difference between the inner and outer surfaces of cell membranes at rest?
1. positive;
2. negative;
3. the potential difference is zero.
What ions contribute to the creation of the resting potential of cell membranes?
1. Na⁺ and Cl - ions;
2. K⁺ ions
3. Ca 2+, K⁺ and Cl - ions;
4. K⁺, Na⁺ and Ca 2+ ions.
25. The presence of capacitive properties in biological membranes is confirmed by the fact that:
1. the current strength is ahead of the applied voltage in phase;
2. the current is out of phase with the applied voltage;
3. The current is in phase with the applied voltage.
26. Indicate the correct statements:
1) The diffusion of charged particles through a membrane obeys the Fick equation.
2) The diffusion of charged particles through the membrane obeys the Nernst equation;
3) The diffusion of uncharged particles through the membrane obeys the Nernst equation.
27. Indicate the correct statements:
1) The membrane permeability coefficient for potassium ions is higher than for sodium or chlorine ions when a resting potential is generated on the cell membrane.
2) When an action potential occurs, the permeability coefficient of the membrane for sodium ions has the highest value.
3) When an action potential occurs, the membrane permeability coefficient for chlorine ions has the highest value.
28. Indicate the correct statements:
1) The Goldman-Hodgkin-Katz equation describes the occurrence of only the resting potential, but not the action potential.
2) The Goldman-Hodgkin-Katz equation describes the occurrence of only the action potential, but not the resting potential.
3) The Goldman-Hodgkin-Katz equation describes the occurrence of a transmembrane potential difference across membranes both in the case of the generation of resting potentials and action potentials.
Let the ratio of the concentrations of potassium ions on opposite sides of the membrane be equal to 10 and the membrane is selectively permeable to potassium. The resulting transmembrane potential difference is 60 mV. What will be the potential difference if we replace potassium ions with calcium ions in the same concentrations and make the membrane selectively permeable to calcium?
30. At rest, the cell membrane:
1.impermeable to Na⁺ and K⁺ ions;
2. permeable to Na⁺ ions 25 times more than for K⁺ ions;
3. permeable to K⁺ ions 25 times more than for Na⁺ ions;
4.equally permeable to Na⁺ and K⁺ ions.
31. Na⁺ - K⁺ pump transfers:
1. 3 K⁺ outside, 2 Na⁺ inside the cell;
2. 3 Na⁺ inside the cell, 2 K⁺ outside;
3. 3 Na⁺ outside, 2 K⁺ inside the cell;
4. 3 K⁺ inside the cell, 2 Na⁺ outside.
32. The Fick equation describes:
1. passive transport;
2. transport of non-electrolytes;
3. ion transport;
4. active transport.
33. For the occurrence of a transmembrane potential difference, it is necessary and sufficient to fulfill the following two conditions:
1) the membrane must contain integral proteins;
2) the membrane must contain surface proteins;
3) there must be selective permeability of ions through the membrane;
4) the concentrations of ions on both sides of the membrane must be different;
1. Methods for studying membrane permeability:
A. Osmotic method
B. Calorimetric method
C. Indicator method
D. Electron microscopic method
E. Radioisotope method
F. Conductivity Measurement Method
2. The concept of transport includes:
A. The ability of the membrane to pass a given substance
B. Method of penetration of a substance through a membrane
C. Kinetics of substance penetration through the membrane
3. Transport carried out against the gradient with the expenditure of macroerg energy is called:
A. Active
B. Passive
C. Electrogenic
4. Active mode of transport differs from passive mode:
A. Direction relative to the concentration gradient
B. Energy use
C. Type of transferred ions
5. The transfer of two ions in opposite directions by an ion transport system is called:
A. Uniport
B. Simport
C. Antiport
6. Simple diffusion is:
7. Facilitated diffusion is:
A. The process of spontaneous penetration of a substance through a membrane along a concentration gradient
B. The process of spontaneous penetration of a substance through a membrane against a concentration gradient
C. The process of penetration of a substance through a membrane along a concentration gradient with the participation of a carrier protein
8. The kinetics of the process of diffusion of a substance through the cell membrane is described:
A. The Collender-Berlund equation
B. Fick's equation
C. Bernoulli's equation
9. The kinetics of the facilitated diffusion process is described by the equation:
B. Collender-Berlund
C. Michaelisa-Menten
10. Mechanisms of water penetration through the cell membrane:
A. Through pores formed by integral proteins
B. Through structural defects in the membrane - kinks
C. By dissolution in the lipid bilayer
11. Osmosis is the movement of water through a membrane:
12. Oncotic pressure is:
A. Osmotic pressure inside the cell
B. Protein-mediated component of osmotic pressure
C. Osmotic pressure in malignant tumor cells
13. Filtration is the movement of water through a membrane:
A. To an area of lower hydrostatic pressure
B. To an area of lower concentration of dissolved substances
C. To an area of higher concentration of dissolved substances
14. Cell membranes perform the following functions:
A. Compartmentation
B. Receptor
C. Transport
D. Conduction of nerve impulses
E. Muscle contraction
F. Intercellular interactions
15. The composition of biomembranes includes:
C. Glycoproteins
16. Membrane lipids are represented by the following classes:
A. Phospholipills
B. Glycoproteins
C. Glycolipids
D. Steroids
17. Lipid molecules are:
A. Hydrophobic compounds
B. Hydrophilic compounds
C. Amphiphilic compounds
18. Phase transitions in the membrane occur between the following states:
A. Gel – sol
B. Gel - liquid phase
C. Liquid crystal - gel
19. Based on their location in the membrane, proteins are divided into:
A. Peripheral
B. Integral
C. Enzymatic
D. Semi-integral
E. Monotopic
20. Membrane proteins make up the following functional groups (indicate the wrong answer):
A. Enzymatic
B. Cytoskeletal proteins
C. Contractiles
D. Receptors
21. Lipids can modify the structure of membrane proteins:
A. Secondary
B. Tertiary
C. Quaternary
22. A mosaic membrane model was proposed by:
A. Singer and Nicholson
B. Danieli and Devson
C. Warburg and Nigilein
D. Gorter and Grendel
23. Modern ideas about the structure of membranes correspond to:
A. Lipid bilayer model
B. Mosaic model
C. Unitary model
Under natural conditions, the transfer of internal energy to heat exchange always occurs in a strictly defined direction: from a body with a higher temperature to a body with a lower temperature. When the temperatures of the bodies become the same, a state of thermal equilibrium occurs: the bodies exchange energy in equal quantities.
The set of phenomena associated with the transition of thermal energy from one part of space to another, which is caused by the difference in the temperatures of these parts, is generally called heat exchange. There are several types of heat transfer in nature. There are three ways to transfer heat from one body to another: thermal conductivity, convection and radiation.
Thermal conductivity.
Place the end of a metal rod in the flame of the alcohol lamp. We attach several matches to the rod at equal distances from each other using wax. When one end of the rod is heated, the wax balls melt and the matches fall off one after another. This indicates that internal energy is transferred from one end of the rod to the other.
Figure 1 Demonstration of the thermal conduction process
Let's find out the reason for this phenomenon.
When the end of the rod is heated, the intensity of movement of the particles that make up the metal increases, and their kinetic energy increases. Due to the randomness of thermal motion, they collide with slower particles of the adjacent cold layer of metal and transfer part of their energy to them. As a result, internal energy is transferred from one end of the rod to the other.
The transfer of internal energy from one part of a body to another as a result of the thermal movement of its particles is called thermal conductivity.
Convection
The transfer of internal energy by thermal conduction occurs mainly in solids. In liquid and gaseous bodies, the transfer of internal energy is carried out in other ways. Thus, when water is heated, the density of its lower, hotter layers decreases, while the upper layers remain cold and their density does not change. Under the influence of gravity, denser cold layers of water fall down, and heated ones rise up: mechanical mixing of cold and heated layers of liquid occurs. All the water warms up. Similar processes occur in gases.
The transfer of internal energy due to mechanical mixing of heated and cold layers of liquid or gas is called convection.
The phenomenon of convection plays a big role in nature and technology. Convection currents cause constant mixing of air in the atmosphere, due to which the composition of the air in all places on Earth is almost the same. Convection currents provide a continuous supply of fresh portions of oxygen to the flame during combustion processes. Due to convection, the air temperature in residential premises is equalized during heating, as well as air cooling of devices during the operation of various electronic equipment.
Figure 2 Heating and equalization of air temperature in residential premises during heating due to convection
Radiation
The transfer of internal energy can also occur through electromagnetic radiation. This is easy to discover through experience. Let's plug in the electric heating stove. It warms our hand well when we bring it not only from above, but also from the side of the stove. The thermal conductivity of the air is very low, and convection currents rise upward. In this case, the energy from the helix heated by electric current is mainly transferred by radiation.
The transfer of internal energy by radiation is carried out not by particles of matter, but by particles of the electromagnetic field - photons. They do not exist “ready-made” inside atoms, like electrons or protons. Photons arise when electrons move from one electron layer to another, located closer to the nucleus, and at the same time carry with them a certain portion of energy. Reaching another body, photons are absorbed by its atoms and completely transfer their energy to them.
The transfer of internal energy from one body to another due to its transfer by particles of the electromagnetic field - photons, is called electromagnetic radiation. Any body whose temperature is higher than the ambient temperature radiates its internal energy into the surrounding space. The amount of energy emitted by a body per unit time increases sharply with increasing temperature.
Figure 3 Experiment illustrating the transfer of internal energy of a hot kettle through radiation
Figure 4 Radiation from the Sun
Transport phenomena in thermodynamically nonequilibrium systems. Thermal conductivity
In thermodynamically nonequilibrium systems, special irreversible processes arise, called transfer phenomena, as a result of which spatial transfer of energy, mass, and momentum occurs. Transport phenomena include thermal conductivity (caused by energy transfer), diffusion (caused by mass transfer), and internal friction (caused by momentum transfer). For these phenomena, the transfer of energy, mass and momentum always occurs in the direction opposite to their gradient, i.e. the system approaches a state of thermodynamic equilibrium.
If in one region of the gas the average kinetic energy of molecules is greater than in another, then over time, due to constant collisions of molecules, a process of equalization of the average kinetic energies of molecules occurs, i.e., in other words, equalization of temperatures.
The process of energy transfer in the form of heat obeys Fourier’s law of thermal conductivity: the amount of heat q that is transferred per unit time through a unit area is directly proportional 
- temperature gradient equal to the rate of temperature change per unit length x in the direction of the normal to this area:
, (1)
where λ is the thermal conductivity coefficient or thermal conductivity. The minus sign shows that during thermal conductivity, energy is transferred in the direction of decreasing temperature. Thermal conductivity λ is equal to the amount of heat transferred through a unit area per unit time with a temperature gradient equal to unity.
It is obvious that the heat Q passed by thermal conduction through the area S during time t is proportional to the area S, time t and temperature gradient 
:
It can be shown that
(2)
where with V - specific heat capacity of gas at constant volume(the amount of heat required to heat 1 kg of gas by 1 K at constant volume), ρ - gas density,<υ>- arithmetic average speed of thermal movement of molecules,<l> - average free path.
Those. it is clear on what reasons the amount of energy transferred by thermal conduction, for example, from a room through a wall to the street, depends. Obviously, the more energy is transferred from the room to the street, the larger the wall area S, the greater the temperature difference Δt in the room and outside, the longer the time t for heat exchange between the room and the street, and the smaller the wall thickness (thickness of the layer of substance) d : 
~
.
In addition, the amount of energy transferred by thermal conduction depends on the material from which the wall is made. Different substances under the same conditions transfer different amounts of energy by thermal conductivity. The amount of energy that is transferred by thermal conduction through each unit area of a layer of a substance per unit time when the temperature difference between its surfaces is 1 ° C and when its thickness is 1 m (unit length) can serve as a measure of the ability of a substance to transfer energy by thermal conductivity. This value is called the thermal conductivity coefficient. The higher the thermal conductivity coefficient λ, the more energy is transferred by the layer of substance. Metals have the greatest thermal conductivity, liquids have somewhat less. Dry air and wool have the lowest thermal conductivity. This explains the heat-insulating properties of clothing in humans, feathers in birds and wool in animals.