Preparation for the test. Preparing for the test The assessment system for exam work in physics
To complete the examination work in physics, 4 hours (240 minutes) are allotted. The work consists of 3 parts, including 35 tasks.
- Part 1 contains 25 tasks (A1-A25). For each task there are 4 possible answers, of which only one is correct.
- Part 2 contains 4 tasks (B1-B4), in which the answer must be written down as a set of numbers.
- Part 3 consists of 6 tasks (C1-C6), for which detailed solutions are required.
When making calculations, it is allowed to use a non-programmable calculator.
Read each task carefully and the suggested answer options, if any. Answer only after you understand the question and have considered all possible answers. Complete the tasks in the order in which they are given. If a task is difficult for you, skip it. You can return to missed tasks if you have time. The points you receive for completed tasks are summed up. Try to complete as many tasks as possible and score the most points.
Below is reference information that you may need when doing the job.
Decimal prefixes
Naimenov | Designate | Factor- | Naimenov | Designate | Factor- |
| Milli | |||||
PART 1
When completing tasks in Part 1, in answer form No. 1, under the number of the task you are performing (A1-A25), put the “×” sign in the box whose number corresponds to the number of the answer you have chosen.
A1 Four bodies moved along the Ox axis. The table shows the dependence of their coordinates on time.
Which body could have a constant velocity and different from zero?
1) 1 2) 2 3) 3 4) 4
A2 Two forces act on a body in an inertial frame of reference. Which of the vectors shown in the right figure correctly indicates the direction of acceleration of the body in this reference frame?
1) 1 2) 2 3) 3 4) 4
A3 The figure shows a graph of the dependence of the modulus of elastic force on the elongation of the spring. What is the spring stiffness?
A4 Two bodies move along mutually perpendicular intersecting lines, as shown in the figure. The modulus of the first body is p1 = 4 kg⋅m/s, and the second body is p2 = 3 kg⋅m/s. What is the modulus of momentum of the system of these bodies after their absolutely inelastic impact?
1) 1 kg⋅ m/s
2) 4 kg m/s
3) 5 kg⋅m/s
4) 7 kg⋅m/s
A5 A car weighing 103 kg moves at a speed of 10 m/s. What is the kinetic energy of the car?
1) 10 5 J
2) 10 4 J
3) 5⋅10 4 J
4) 5⋅10 3 J
A6 The period of oscillation of a spring pendulum is 1 s. What will be the period of oscillation if the mass of the pendulum's load and the stiffness of the spring are increased by 4 times?
1) 1 s
2) 2 s
3) 4 s
4) 0.5 s
A7 On the last kilometer of the braking distance, the speed of the train decreased by 10 m/s. Determine the speed at the beginning of braking if the total braking distance of the train was 4 km, and the braking was uniformly slow.
1) 20 m/s
2) 25 m/s
3) 40 m/s
4) 42 m/s
A8 When the gas temperature in a sealed vessel decreases, the gas pressure decreases. This decrease in pressure is due to the fact that
1) the energy of thermal motion of gas molecules decreases
2) the energy of interaction of gas molecules with each other decreases
3) the randomness of the movement of gas molecules decreases
4) the size of gas molecules decreases as it cools
A9 There is a narrow pan of water on the gas stove, covered with a lid. If you pour water from it into a wide pan and also close it, the water will boil noticeably faster than if it remained in a narrow one. This fact is explained by the fact that
1) the heating area increases and, therefore, the rate of water heating increases
2) the required saturated vapor pressure in the bubbles increases significantly and, therefore, the water at the bottom must be heated to a lower temperature
3) the surface area of water increases and, therefore, evaporation occurs more actively
4) the depth of the water layer noticeably decreases and, therefore, steam bubbles reach the surface faster
A10 The relative humidity of the air in the cylinder under the piston is 60%. The air was isothermally compressed, reducing its volume by half. The relative air humidity became equal to
1) 120%
2) 100%
3) 60%
4) 30%
A11 Four metal bars were placed close to each other, as shown in the figure. The arrows indicate the direction of heat transfer from block to block. Bar temperatures are currently 100°C, 80°C, 60°C, 40°C. The bar has a temperature of 60°C
1) A
2) B
3) C
4) D
A12 At a temperature of 10°C and a pressure of 10 5 Pa, the gas density is 2.5 kg/m 3. What is the molar mass of the gas?
1) 59 g/mol
2) 69 g/mol
3) 598 kg/mol
4) 5.8-10 -3 kg/mol
A13 An uncharged metal body was introduced into a uniform electrostatic field, and then divided into parts A and B (see figure). What electrical charges do these parts have after separation?
1) A - positive, B - will remain neutral
2) A - will remain neutral, B - negative
3) A - negative, B - positive
4) A - positive, B - negative
A14 A direct electric current flows through a conductor. The value of the charge passing through the conductor increases over time according to the graph presented in the figure. The current strength in the conductor is equal to
1) 36 A
2) 16 A
3) 6 A
4) 1 A
A15 The inductance of a turn of wire is 2⋅10 -3 H. At what current strength in the coil is the magnetic flux through the surface bounded by the coil equal to 12 mWb?
1) 24⋅10 -6 A
2) 0.17 A
3) 6 A
4) 24 A
A16 The figure shows the induction vector B → magnetic field in an electromagnetic wave and the vector in the Cartesian coordinate system c→ the speed of its spread. The direction of the electric field strength vector E → in the wave coincides with the arrow
1) 1
2) 2
3) 3
4) 4
A17 Students investigated the relationship between the speeds of a car and its image in a plane mirror in the reference frame associated with the mirror (see figure). Projection onto the axis Oh the speed vector with which the image moves in this reference system is equal to
1) - 2v
2) 2v
3) v
4) - v
A18 Two point light sources S 1 and S 2 are close to each other and create a stable interference pattern on the remote screen E (see figure). This is possible if S 1 and S 2 are small holes in an opaque screen, illuminated
1) each with its own sunbeam from different mirrors
2) one - an incandescent light bulb, and the second - a burning candle
3) one with blue light and the other with red light
4) light from the same point source
A19 Two point positive charges q 1= 200 nC and q 2= 400 nC are in vacuum. Determine the magnitude of the electric field strength of these charges at point A, located on a straight line connecting the charges, at a distance L from the first and 2L from the second charge. L= 1.5 m.
1) 1200 kV/m
2) 1200 V/m
3) 400 kV/m
4) 400 V/m
A20 The figure shows several of the lowest energy levels of the hydrogen atom. Can an atom in a state E 1, absorb a photon with an energy of 3.4 eV?
1) yes, in this case the atom goes into the state E 2
2) yes, in this case the atom goes into the state E 3
3) yes, in this case the atom is ionized, decaying into a proton and an electron
4) no, the photon energy is not enough for the atom to transition to an excited state
A21 What fraction of radioactive nuclei decays after a time interval equal to two half-lives?
1) 100%
2) 75%
3) 50%
4) 25%
A22 Radioactive polonium, having undergone one α-decay and two β-decays, turned into an isotope
1) lead 2) polonium 3) bismuth 4) thallium
A23 One way to measure Planck's constant is based on determining the maximum kinetic energy of electrons during the photoelectric effect by measuring the voltage that retards them. The table shows the results of one of the first such experiments.
Holding voltage U, V | ||
Light frequency v, 10 14 Hz |
Planck's constant according to the results of this experiment is equal to
1) 6.6⋅10 -34 J⋅s
2) 5.7⋅10 -34 J⋅s
3) 6.3⋅10 -34 J⋅s
4) 6.0⋅10 -34 J⋅s
A24 When measuring current in a spiral wire R four students connected the ammeter in different ways. The result is shown in the figure. Indicate the correct ammeter connection.
A25 When conducting an experiment, the student investigated the dependence of the elastic modulus of the spring on the length of the spring, which is expressed by the formula F(l) = k|l − l 0 | , Where l 0- length of the spring in an undeformed state.
The graph of the obtained dependence is shown in the figure.
Which of the statements correspond(s) to the results of the experiment?
A. The undeformed length of the spring is 3 cm.
B. The spring stiffness is 200 N/m.
1) only A
2) only B
3) both A and B
4) neither A nor B
PART 2
The answer to the tasks in this part (B1-B4) is a sequence of numbers. Enter the answers first into the text of the work, and then transfer them to answer form No. 1 to the right of the number of the corresponding task, starting from the first cell, without spaces or any additional characters. Write each number in a separate box in accordance with the samples given in the form.
IN 1 As a result of the transition from one circular orbit to another, the centripetal acceleration of the Earth's satellite decreases. How do the radius of the satellite’s orbit, the speed of its orbital motion, and the period of revolution around the Earth change as a result of this transition? For each quantity, determine the corresponding nature of the change:
1) increased
2) decreased
3) has not changed
B2 The temperature of the heat engine refrigerator was increased, leaving the heater temperature the same. The amount of heat received by the gas from the heater per cycle has not changed. How did the efficiency of the heat engine, the amount of heat transferred by the gas per cycle to the refrigerator, and the work of the gas per cycle change?
For each quantity, determine the corresponding nature of the change:
1) increased
2) decreased
3) has not changed
Write down the selected numbers for each physical quantity in the table. The numbers in the answer may be repeated.
B3 A beam of light passes from water to air. The frequency of the light wave is ν, the speed of light in water is v, the refractive index of water relative to air - n. Establish a correspondence between physical quantities and formulas by which they can be calculated. For each position in the first column, select the corresponding position in the second and write down the selected numbers in the table under the corresponding letters.
| A | B |
AT 4 
The oscillating circuit capacitor is connected to a constant voltage source (see figure). Graphs A and B represent changes in physical quantities characterizing oscillations in the circuit after switch K is moved to position 2. Establish a correspondence between the graphs and the physical quantities, the dependence of which on time these graphs can represent. For each position in the first column, select the corresponding position in the second and write down the selected numbers in the table under the corresponding letters.
| A | B |
Do not forget to transfer all answers to answer form No. 1.
PART 3
Tasks C1-C6 are problems, the complete solution of which must be written down in answer form No. 2. It is recommended to carry out a preliminary solution on a draft. When completing the solution in answer form No. 2, first write down the task number (CI, C2, etc.), and then the solution to the corresponding problem. Write down your answers clearly and legibly.
C1
A complete correct solution to each of the problems C2-C6 must include laws and formulas, the use of which is necessary and sufficient to solve the problem, as well as mathematical transformations, calculations with a numerical answer and, if necessary, a drawing explaining the solution.
C2 Puck mass m N m
C3 p 1= 4·10 5 Pa. The distance from the bottom of the vessel to the piston is L S= 25 cm 2. As a result of slow heating, the gas received an amount of heat Q= 1.65 kJ, and the piston has moved a distance x F tr = 3 10 3 N. Find L
C4 During laboratory work, the student assembled an electrical circuit according to the diagram in the figure. Resistance R 1 and R 2 are equal to 20 Ohms and 150 Ohms respectively. The resistance of a voltmeter is 10 kOhm, and that of an ammeter is 0.4 Ohm. The emf of the source is 36 V, and its internal resistance is 1 Ohm.
C5
C6 t= 8·10 -4 s emits N S P
Assessment system for examination work in physics
PART 1
For the correct answer to each task in Part 1, 1 point is given. If two or more answers are indicated (including the correct one), an incorrect answer or no answer - 0 points.
Job No. | Answer | Job No. | Answer |
PART 2
A task with a short answer is considered completed correctly if the sequence of numbers is correctly indicated in tasks B1-B4.
For a complete correct answer, 2 points are given, 1 point - one mistake was made; for an incorrect answer (more than one error) or lack thereof - 0 points.
Job No. | Answer |
PART 3
CRITERIA FOR EVALUATING COMPLETION OF TASKS WITH DETAILED ANSWER
C1 The figure shows an electrical circuit consisting of a galvanic element, a rheostat, a transformer, an ammeter and a voltmeter. At the initial moment of time, the rheostat slider is installed in the middle and motionless. Based on the laws of electrodynamics, explain how instrument readings will change as the rheostat slider moves to the left. Neglect self-induction emf compared to ε.
Sample possible solution |
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1. While moving the rheostat slider, the ammeter readings will gradually increase, and the voltmeter will record the voltage at the ends of the secondary winding. Note: An explanation of the instrument readings at the far left is not required for a complete answer. (When the engine reaches the extreme left position and its movement stops, the ammeter will show a constant current in the circuit, and the voltage measured by the voltmeter will be zero.) 2. As the slider moves to the left, the circuit resistance decreases and the current increases in accordance with Ohm's law for a complete circuit 3. A change in the current flowing through the primary winding of the transformer causes a change in the induction of the magnetic field created by this winding. This leads to a change in the magnetic flux through the secondary winding of the transformer. 4. In accordance with Faraday’s law of induction, an induced emf occurs | |
Points |
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A complete correct solution is given, including the correct answer (in this case - a change in instrument readings, point 1), and a complete correct explanation (in this case - points 2-4) indicating the observed phenomena and laws (in this case - electromagnetic induction , Faraday's law of induction, Ohm's law for a complete circuit). | 3 |
The solution is given and the correct answer is given, but there is one of the following shortcomings: The explanation contains only general reasoning without reference to the specific situation of the problem, although all the necessary physical phenomena and laws are indicated; | 2 |
Reasoning is given indicating physical phenomena and laws, but an incorrect or incomplete answer is given; | 1 |
| 0 | |
Where R- resistance of the external circuit.
in the secondary winding, and therefore the voltage U at its ends, recorded by a voltmeter.C2 Puck mass m begins to move along the channel AB from point A from a state of rest. Point A is located above point B at a height N= 6 m. During movement along the chute, the mechanical energy of the washer due to friction decreases by ΔE = 2J. At point B, the puck flies out of the chute at an angle α = 15° to the horizontal and falls to the ground at point D, located on the same horizontal line as point B (see figure). BD = 4 m. Find the mass of the washer m. Neglect air resistance.
Sample possible solution |
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1. The speed of the puck at point B is determined from the balance of its energy at points A And IN taking into account friction losses:
From here: 2. Time of flight of the puck from the point IN exactly D:
reference with the origin at the point IN. 3. The flight range BD is determined from the expression for the horizontal coordinates of the puck in the same reference system: 4. Substituting into the expression for BD meaning v 2, we get
5. From here we find the mass of the washer: Answer: m= 0.1 kg. |
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Criteria for assessing assignment completion | Points |
The complete correct solution is given, including the following elements: The use of which is necessary to solve the problem in the chosen way (in this solution - the law of conservation of energy and formulas for the kinematics of free fall); 2) the necessary mathematical transformations and calculations leading to the correct numerical answer are carried out, and the answer is presented; in this case, a solution “in parts” is allowed (with intermediate calculations). | |
| 2 |
Records are presented that correspond to one of the following cases:
| 1 |
| 0 | |
Where y- vertical coordinate of the washer in the system
C3 A monatomic ideal gas is contained in a horizontal cylindrical vessel closed by a piston. Initial gas pressure p 1 = 4·10 5 Pa. The distance from the bottom of the vessel to the piston is L. Piston cross-sectional area S= 25 cm 2. As a result of slow heating, the gas received an amount of heat Q = 1.65 kJ, and the piston moved a distance x= 10 cm. When the piston moves, a frictional force of magnitude acts on it from the side of the walls of the vessel F tr = 3 10 3 N. Find L. Assume that the vessel is in a vacuum.
Sample possible solution |
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1. The piston will move slowly if the force of gas pressure on the piston and the friction force from the walls of the vessel balance each other: p 2 S = F tr,
2. Therefore, when the gas is heated, the piston will remain motionless until the gas pressure reaches the value p 2. In this process, the gas receives an amount of heat Q 12. Q = Q 12 +Q 23 = (U 3 −U 1) + p 2 Sx = (U 3 −U 1) + F tr x. 4) Internal energy of a monatomic ideal gas:
in final state. 5) From paragraphs. 3, 4 we get Answer: L= 0.3 m. |
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Criteria for assessing assignment completion | Points |
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— an error was made in the necessary mathematical transformations or calculations; | |
Records are presented that correspond to one of the following cases: — Only provisions and formulas expressing physical laws, the application of which is necessary to solve the problem, are presented, without any transformations with their use aimed at solving the problem and the answer; | |
All cases of solution that do not correspond to the above | |
in its initial state,
C4 During laboratory work, the student assembled an electrical circuit according to the diagram in the figure. Resistances R 1 and R 2 are 20 Ohms and 150 Ohms, respectively. The resistance of a voltmeter is 10 kOhm, and that of an ammeter is 0.4 Ohm. The emf of the source is 36 V, and its internal resistance is 1 Ohm.
The figure shows the instrument scales with the readings that the student received. Are the instruments working properly or are some of them giving incorrect readings?
Sample possible solution |
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To determine the current strength, we use Ohm's law for a complete circuit. The voltmeter and resistor R 1 are connected in parallel. Hence, The ammeter shows a current strength of about 0.22 A. The ammeter scale division value is 0.02 A, which is greater than the deviation of the readings from the calculation. Hence, The ammeter gives correct readings. From here U = I ⋅ R 1 = 0.21⋅20 = 4.2 (V). The voltmeter shows the voltage |
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Criteria for assessing assignment completion | Points |
The complete correct solution is given, including the following elements: 1) correctly written formulas expressing physical laws, the application of which is necessary to solve the problem in the chosen way (in this solution - Ohm’s law for the complete circuit and for a section of the circuit, formulas for calculating the resistance of a section of a circuit for series and parallel connection of conductors); 2) the necessary mathematical transformations and calculations leading to the correct numerical answer are carried out, and the answer is presented. In this case, a solution is allowed “in parts” (with intermediate calculations). | |
The presented solution contains paragraph 1 of the complete solution, but also has one of the following disadvantages: There was an error in the required mathematical transformations or calculations; | |
Records are presented that correspond to one of the following cases: Only provisions and formulas expressing physical laws, the application of which is necessary to solve the problem, are presented, without any transformations with their use aimed at solving the problem and the answer; | |
All cases of solution that do not meet the above criteria for scoring 1, 2, 3 points. | |
C5 A small load suspended on a thread 2.5 m long undergoes harmonic oscillations, at which its maximum speed reaches 0.2 m/s. Using a converging lens with a focal length of 0.2 m, the image of the oscillating mass is projected onto a screen located at a distance of 0.5 m from the lens. The main optical axis of the lens is perpendicular to the plane of oscillation of the pendulum and the plane of the screen. Determine the maximum displacement of the load image on the screen from the equilibrium position.
Sample possible solution |
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When the pendulum oscillates, the maximum speed of the load is v can be determined from the law of conservation of energy: maximum lifting height. Maximum deviation angle where A- amplitude of oscillations (amplitude of displacement). From here Amplitude A 1 oscillation of the displacement of the cargo image on a screen located at a distance b from the plane of a thin lens, proportional to the amplitude A vibrations of a load moving at a distance A from the plane of the lens: Distance a is determined by the thin lens formula: Hence,
Answer: A 1 = 0.15 m. |
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Criteria for assessing assignment completion | Points |
The complete correct solution is given, including the following elements: 1) the formulas expressing physical laws are written correctly, the use of which is necessary to solve the problem in the chosen way (in this solution - the law of conservation of energy, the formula for magnifying a thin lens and the formula for a thin lens); 2) the necessary mathematical transformations and calculations leading to the correct numerical answer are carried out, and the answer is presented. In this case, a solution is allowed “in parts” (with intermediate calculations). | |
The presented solution contains point 1 of the complete solution, but also has one of the following disadvantages: There was an error in the required mathematical transformations or calculations; | |
Records are presented that correspond to one of the following cases: Only provisions and formulas expressing physical laws, the application of which is necessary to solve the problem, are presented, without any transformations with their use aimed at solving the problem and the answer; | |
All cases of solution that do not correspond to the above | |
where 
C6 A monochromatic beam of parallel rays is created by a source, which, in a time Δ t= 8·10 -4 s emits N= 5·10 14 photons. Photons fall normally onto the site S= 0.7 cm 2 and create pressure P= 1.5·10 -5 Pa. In this case, 40% of photons are reflected, and 60% are absorbed. Determine the wavelength of the radiation.
Sample possible solution |
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Expression for light pressure: (Formula (1) follows from.) Formulas for changing the momentum of a photon during reflection and absorption of rays: Expression for photon momentum: Expression for the radiation wavelength: |
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Criteria for assessing assignment completion | Points |
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The complete correct solution is given, including the following elements: 1) formulas expressing physical laws are written correctly, the use of which is necessary to solve the problem using the chosen method (in this solution - formulas for light pressure, photon momentum, Newton's II law); 2) the necessary mathematical transformations and calculations leading to the correct numerical answer are carried out, and the answer is presented. In this case, a solution is allowed “in parts” (with intermediate calculations). | |||
The presented solution contains paragraph 1 of the complete solution, but also has one of the following disadvantages: There was an error in the required mathematical transformations or calculations; | |||
Records are presented that correspond to one of the following cases: Only provisions and formulas expressing physical laws, the application of which is necessary to solve the problem, are presented, without any transformations with their use aimed at solving the problem and the answer; | |||
All cases of solution that do not correspond to the above | |||
A1. There is a certain amount of ideal gas in the vessel. How will the temperature of the gas change if it goes from state 1 to state 2 (see figure)?
1) T 2 = 4T 1 2) T 2 = T 1 /4 3) T 2 = 4T 1 /3 4) T 2 = 3T 1 /4
A2. The relative humidity of the air in the cylinder under the piston is 60%. The air was isothermally compressed, reducing its volume by half. The relative air humidity became equal to
1) 120% 2) 100% 3) 60% 4) 30%A3. An uncharged metal body was introduced into a uniform electrostatic field and then divided into parts A and B (see figure). What electrical charges do these parts have after separation?
1) A – positive, B – will remain neutral
2) A – will remain neutral, B – negative
3) A – negative, B – positive
4) A – positive, B – negativeA4. When measuring the current in a coil of wire R, four students connected the ammeter in different ways. The result is shown in the figure. Indicate the correct ammeter connection.
A5. To a direct current source with EMF E = 12 V and internal resistance r = 2 Ohms, n = 5 light bulbs with resistance R = 2 Ohms each are connected in parallel. What is the current flowing through each light bulb?
1) 0.5 A 2) 1.0 A 3) 1.5 A 4) 2.0 AB1.
B2.
C1. During laboratory work, the student assembled an electrical circuit according to the diagram in the figure. Resistances R 1 and R 2 are 20 and 150 Ohms, respectively. The resistance of the voltmeter is 10 kOhm, and the ammeter is 0.4 Ohm. The emf of the source is 36 V, and its internal resistance is 1 Ohm. The figure shows the instrument scales with the readings that the student received. Are the instruments working properly or are any of them giving incorrect readings?
We will discuss answers and solutions to these problems in class on Tuesday, April 26, 2011.
1 option
1. The figure shows two thermometers used to determine the relative humidity of the air using a psychrometric table in which the air humidity is indicated as a percentage.
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The relative humidity of the air in the room in which the shooting was carried out is equal to
2. Relative air humidity is 42%, partial vapor pressure at temperature is 980Pa . The saturated vapor pressure at a given temperature is (round the answer to whole numbers)
3.The relative humidity of the air in the cylinder under the piston is 60%. The air was isothermally compressed, reducing its volume by half. Relative air humidity became:
1) isobarically increasing the temperature
2) adding another gas to the vessel
3) increasing the volume of steam
4) reducing the volume of steam
5. The relative humidity in the room is 40%. What is the concentration ration water molecules in room air and concentrationn n.p.. water molecules in saturated water vapor at the same temperature?
1) n is 2.5 times less
2) n is 2.5 times greater
3) n is 40% less
4) n is 40% more
6. What is the relative humidity at a temperature of 20C, if the dew point is 12C. The pressure of saturated water vapor at 20C is 2.33 kPa, and at 12C it is 1.40 kPa. Express your answer as a percentage and round to the nearest whole number.
7. p T . DotA This graph shows the state of steam in a closed vessel. What is the relative humidity of the air in this container? Round your answer to the nearest whole percentage.
8. Relative humidity in a closed vessel is 30%. What will the relative humidity be if the volume of the vessel at a constant temperature is reduced by 3 times? (Give your answer as a percentage.)
9. During the day, at a temperature of 19 °C, the relative air humidity was 70%. How much water in the form of dew will be released from each cubic meter of air if the temperature dropped to 7 °C at night?
10. The relative humidity of water vapor in a vessel at a temperature of 100 °C is 62%. What is the density of this vapor? (Give your answer in kg/m 3 , rounded to the nearest hundredths.)
Option 2
1. The figure shows two thermometers used to determine the relative humidity of the air using a psychrometric table in which humidity is indicated as a percentage.
The psychrometric table is presented below.
Difference between dry and wet bulb readings
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What was the relative humidity at the time the photo was taken? (Give your answer in percentage.)
2. The saturated vapor pressure at a temperature of 15 °C is 1.71 kPa. If the relative humidity is 59%, what is the partial pressure of vapor at a temperature of 15 °C? (Give your answer in pascals.)
3. The relative humidity of the air in the cylinder under the piston is 50%. The air was isothermally compressed, reducing its volume by 3 times. What was the relative humidity? (Give your answer as a percentage.)
4. There is unsaturated steam in the vessel under the piston. It can be converted to saturated,
1) adding another gas to the vessel
2) reducing the volume of steam
3) increasing the volume of steam
4) isobarically increasing the temperature
5. The relative humidity in the room is 40%. What is the ratio of the concentration of water molecules in the air of a room to the concentration of water molecules in saturated water vapor at the same temperature?
6. What is the relative humidity at a temperature of 19 °C if the dew point is 7 °C? The pressure of saturated water vapor at 19 °C is 2.2 kPa, and at 7 °C it is 1.00 kPa. Express your answer as a percentage and round to the nearest whole number.
7. Relative humidity in a closed vessel is 30%. What will the relative humidity become if the volume of the vessel at a constant temperature is reduced by 1.5 times? (Give your answer as a percentage.)
8. In a room at a temperature of 20 °C, the relative humidity is 20%. How much water do you need to evaporate to increase humidity to 50%? Room volume 40 m3.
9. The relative humidity of water vapor in a vessel at a temperature of 100 °C is 81%. What is the density of this vapor? Express your answer inkg/m3and round to the nearest hundredths.
10. The figure shows the pressure dependencep saturated water vapor on temperatureT . Point A on this graph indicates the state of steam in a closed vessel. What is the relative humidity (in percent) in this container? Round your answer to a whole number.
Test No. 18 Humidity and efficiency of a heat engine
Task 1. The steam pressure in the room at a temperature of 756 Pa. The saturated vapor pressure at the same temperature is 880 Pa. Relative humidity is (round answer to whole numbers)
1) 1% 2) 60% 3) 86% 4) 100%
Task2. The saturated vapor pressure at temperature is 1.71 kPa. If the relative air humidity is 59%, then the partial pressure of vapor at temperature is equal to (choose the answer that is closest to you)
1) 1 Pa 2) 100 Pa 3) 1000 Pa 4) 10000 Pa
Task 3. A vessel with a movable piston contains water and its saturated steam. The volume of steam was isothermally reduced by 2 times. The concentration of vapor molecules in this case
1) decreased by 2 times 2) did not change 3) increased by 2 times 4) increased by 4 times
Task 4. The relative humidity of the air in the cylinder under the piston is 60%. The air was isothermally compressed, reducing its volume by half. Relative humidity has become
120 % 2) 100 % 3) 60 % 4) 30 %
Task 5. There is unsaturated steam in the vessel under the piston. It can be converted to saturated,
1) increasing the temperature isobarically 2) adding another gas to the vessel 3) increasing the volume of steam
4) reducing the volume of steam
Task 6. The relative humidity in the room is 40%. What is the ratio of the concentration n of water molecules in the air of the room and the concentration of water molecules in saturated water vapor at the same temperature?
1) n is 2.5 times less 2) n is 2.5 times more 3) n is 40% less 4) n is 40% more
Task 7. What is the relative humidity at temperature if the dew point of saturated water vapor at is equal to 2.33 kPa, and at - 1.40 kPa. Express your answer as a percentage and round to the nearest whole number.
1) 60% 2) 50% 3) 40% 4) 75%
Task 8. The figure shows: the dotted line is a graph of the dependence of the pressure of saturated water vapor on temperature, and the solid line is the process of 1-2 changes in the partial pressure of water vapor.
As the partial pressure of water vapor changes in this way, the absolute humidity of the air
1) increases 2) decreases 3) does not change 4) can both increase and decrease
Task 9. Relative humidity in a closed vessel is 30%. What will the relative humidity become if the volume of the vessel at a constant temperature is halved?
1) 60% 2) 45% 3) 15% 4) 30%
Task 10. Relative humidity in a closed vessel is 25%. What will the relative humidity be if the volume of the vessel at a constant temperature is reduced by 3 times?
1) 8% 2) 100% 3) 25% 4) 75%
Task 11. The relative humidity of the air in a vessel closed with a piston is 30%. What will the relative humidity be if the volume of the container is reduced by 3 times by moving the piston at a constant temperature?
Task 12. Is it possible to have an ideal heat engine that receives 50 J from the heater per cycle and does 100 J of useful work? What is the efficiency of such a heat engine?
1) possible, 2) possible, 3) possible, 4) impossible,
Task 13. The temperature of the heater of the heat engine is 1,000 K, the temperature of the refrigerator is 200 K less than that of the heater. The maximum possible efficiency of the machine is
Task 14. The efficiency of a heat engine is 20%. What will it be equal to if the amount of heat received from the heater increases by 25%, and the amount of heat given to the refrigerator decreases by 25%?
1) 25% 2) 30% 3) 39% 4) 52%
Task 15. The table shows the dependence of the efficiency of an ideal heat engine on the temperature of its heater at a constant temperature of the refrigerator. What is the temperature of the refrigerator of this heat engine?
1) 250 K 2) 275 K 3) 300 K 4) 350 K
Task 16. An ideal gas undergoes a cyclic process 1→2→3→4→1, shown in the figure. As a result of this cyclical process
1) the total work done by the gas is zero.
2) the change in internal energy of the gas is zero.
3) the total amount of heat received and released by the gas is zero.
4) all the heat received by the gas in the process 1→2→3 is completely converted into mechanical work.
Task 17. The figure schematically shows the direction of heat transfer during the operation of two ideal heat engines. Which one has more efficiency?
1) the first one 2) the second one 3) both machines have the same efficiency 4) there is no clear answer
Task 18. The figure shows two cyclic processes 1 → 2 →3 →4 → 1 and 5 → 6 → 7 → 8 → 5.
Which of the following statements is true?
A. The work of gas in the case of a cyclic process 1 → 2 → 3 → 4 → 1 is greater than the work of gas in the case of a cyclic process 5 → 6 → 7 → 8 → 5.
B. The change in the internal energy of the gas as a result of the cyclic process 1 → 2 → 3 → 4 → 1 is greater than the change in the internal energy of the gas as a result of the cyclic process 5 → 6 → 7 → 8 → 5.
1) only A 2) both A and B 3) only B 4) neither A nor B
Task 19. Which of the following statements is true?
A. A positive amount of heat cannot spontaneously transfer from a colder body to a warmer one.
B. It is impossible to create a cyclic heat engine, with the help of which the energy received from the heater can be completely converted into mechanical work.
1) only A
2) only B
4) neither A nor B
Task 20. Which of the following statements is/are incorrect?
A. It is possible to transfer energy from a body with a lower temperature to a body with a higher temperature by performing work.
B. The efficiency of a cyclic heat engine is greater than 100%.
1) only A
2) only B