The relative humidity of the air in the cylinder under the piston is 60. Preparation for the test. Assessment system for examination paper in physics
1 option
1. The figure shows two thermometers used to determine the relative humidity of the air using a psychrometric table, in which the humidity of the air 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 humidity is 42%, partial vapor pressure at temperature is 980Pa . Saturated vapor pressure at a given temperature is (round the answer to the nearest integer)
3. The relative humidity of the air in the cylinder under the piston is 60%. The air is isothermally compressed, reducing its volume by half. The relative humidity of the air 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. 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 more
3) n less than 40%
4) n more than 40%
6. What is the relative humidity of the air 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 indicates the state of the vapor in a closed vessel. What is the relative humidity of the air in this container? Round your answer to the nearest whole number of percent.
8. Relative humidity in a closed vessel is 30%. What will be the relative humidity 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 humidity of the air 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 hundredths.)
Option 2
1. The figure shows two thermometers used to determine the relative humidity of the air using a psychrometric table, in which the humidity is indicated as a percentage.
The psychrometric table is presented below.
Difference between dry and wet thermometer readings
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What was the relative humidity of the air at the time the photo was taken? (Give your answer as a percentage.)
2. Saturated vapor pressure at 15°C is 1.71 kPa. If the relative humidity of the air is 59%, what is the partial vapor pressure at 15°C? (Give your answer in pascals.)
3. The relative humidity of the air in the cylinder under the piston is 50%. The air is isothermally compressed, reducing its volume by 3 times. What is the relative humidity of the air? (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 - the concentration of water molecules in room air to the concentration of water molecules in saturated water vapor at the same temperature?
6. What is the relative humidity of the air at 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 - 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 be the relative humidity 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 of the air is 20%. How much water needs to be evaporated to increase humidity to 50%? The volume of the room is 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 hundredths.
10. The figure shows the dependence of pressurep saturated water vapor on temperatureT . Point A on this graph indicates the state of the vapor in a closed vessel. What is the relative humidity of the air (in percent) in this vessel? Round your answer to the nearest whole number.
A1. A vessel contains a quantity of ideal gas. How will the temperature of the gas change if it passes 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 is isothermally compressed, reducing its volume by half. The relative humidity of the air became equal to
1) 120% 2) 100% 3) 60% 4) 30%A3. An uncharged metal body was brought into a uniform electrostatic field, and then divided into parts A and B (see figure). What electric 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 wire spiral R, four students connected an ammeter in different ways. The result is shown in the figure. Specify the correct connection of the ammeter.
A5. To a DC source with EMF E = 12 V and internal resistance r = 2 Ohm, n = 5 light bulbs with resistance R = 2 Ohm each are connected in parallel. What is the current flowing through each 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. The 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 devices working or is one of them giving incorrect readings?
Answers and solutions to these problems will be discussed at the lesson on Tuesday, April 26, 2011.
To complete the examination paper in physics, 4 hours (240 minutes) are allotted. The work consists of 3 parts, including 35 tasks.
- Part 1 contains 25 tasks (A1-A25). Each question has 4 possible answers, of which only one is correct.
- Part 2 contains 4 tasks (B1-B4), in which the answer must be written as a set of numbers.
- Part 3 consists of 6 problems (С1-С6) for which it is required to give detailed solutions.
When calculating, it is allowed to use a non-programmable calculator.
Read each question carefully and the suggested answers, if any. Answer only after you have understood the question and analyzed 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 get for completed tasks are summed up. Try to complete as many tasks as possible and score the most points.
The following are reference data that you may need to get the job done.
Decimal Prefixes
Namenova | designate | Factor- | Namenova | designate | Factor- |
| Milli | |||||
PART 1
When completing the tasks of part 1 in the answer sheet No. 1, under the number of the task you are performing (A1-A25), put the “×” sign in the box, the number of which corresponds to the number of the answer you have chosen.
A1 Four bodies moved along the x-axis. The table shows the dependence of their coordinates on time.
Which of the bodies could have a constant velocity and be 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 the body's acceleration in this frame of reference?
1) 1 2) 2 3) 3 4) 4
A3 The figure shows a graph of the dependence of the modulus of elasticity on the elongation of the spring. What is the stiffness of the spring?
A4 Two bodies move along mutually perpendicular intersecting lines, as shown in the figure. The momentum modulus of the first body p1 = 4 kg⋅m/s, and of the second body 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 with a mass of 103 kg is moving 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 Oscillation period of the spring pendulum 1 s. What will be the period of oscillation if the weight of the pendulum 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 equally slow.
1) 20 m/s
2) 25 m/s
3) 40 m/s
4) 42 m/s
A8 When the temperature of the gas in the sealed vessel decreases, the pressure of the gas 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 when it is cooled
A9 There is a narrow pan with water on the gas stove, closed with a lid. If the water from it is poured into a wide pan and also closed, then 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, consequently, the rate of water heating increases
2) the required saturation 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 the water increases and, consequently, evaporation is more active
4) the depth of the water layer noticeably decreases and, consequently, the vapor bubbles reach the surface faster
A10 The relative humidity of the air in the cylinder under the piston is 60%. The air is isothermally compressed, reducing its volume by half. The relative humidity of the air became equal to
1) 120%
2) 100%
3) 60%
4) 30%
A11 Four metal bars are placed close to each other, as shown in the figure. The arrows indicate the direction of heat transfer from bar to bar. The temperatures of the bars at the moment are 100°C, 80°C, 60°C, 40°C. The temperature of 60 ° C has a bar
1) A
2) B
3) C
4)D
A12 At a temperature of 10°C and a pressure of 10 5 Pa, the density of the gas 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 brought into a uniform electrostatic field, and then divided into parts A and B (see figure). What electric 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 current flows through a conductor. The value of the charge passed through the conductor increases with time according to the graph shown in the figure. The current strength in the conductor is
1) 36 A
2) 16 A
3) 6 A
4) 1 A
A15 The inductance of a coil 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 in the Cartesian coordinate system shows the induction vector B → magnetic field in an electromagnetic wave and the vector c→ speed of its propagation. 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 The students investigated the relationship between the speeds of a car and its image in a flat mirror in a frame of reference associated with the mirror (see figure). Axis projection Oh the vector of the speed with which the image moves, in this frame of reference 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 - with an incandescent bulb, and the second - with 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 q2= 400 nC are in vacuum. Determine the magnitude of the electric field strength of these charges at point A, located on the 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) 1200V/m
3) 400 kV/m
4) 400V/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, while the atom goes into the state E 2
2) yes, while the atom goes into the state E 3
3) yes, while the atom is ionized, decaying into a proton and an electron
4) no, the photon energy is not enough for the transition of the atom to an excited state
A21 What fraction of radioactive nuclei decay after a time interval equal to two half-lives?
1) 100%
2) 75%
3) 50%
4) 25%
A22 Radioactive polonium, having experienced one α-decay and two β-decays, turned into an isotope
1) lead 2) polonium 3) bismuth 4) thallium
A23 One of the ways to measure Planck's constant is based on determining the maximum kinetic energy of electrons during the photoelectric effect by measuring the voltage that delays them. The table shows the results of one of the first such experiments.
Delay 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 wire coil R four students connected the ammeter in different ways. The result is shown in the figure. Specify the correct connection of the ammeter.
A25 During the 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- the length of the spring in the undeformed state.
The graph of the obtained dependence is shown in the figure.
Which of the statements corresponds(s) to the results of the experiment?
A. The length of the spring in the undeformed state is 3 cm.
B. The spring rate 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 of this part (B1-B4) is a sequence of numbers. Write the answers first in the text of the work, and then transfer them to the answer sheet 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 cell 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 movement along the orbit and the period of revolution around the Earth change as a result of this transition? For each value, determine the appropriate nature of the change:
1) increased
2) decreased
3) has not changed
B2 The temperature of the refrigerator of the heat engine was increased, leaving the temperature of the heater 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 change, the amount of heat given off by the gas per cycle to the refrigerator, and the work of the gas per cycle?
For each value, determine the appropriate nature of the change:
1) increased
2) decreased
3) has not changed
Write in the table the selected numbers for each physical quantity. Numbers in the answer may be repeated.
B3 A beam of light passes from water to air. The frequency of the light wave - ν, the speed of light in water - 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 of the first column, select the corresponding position of the second and write down the selected numbers in the table under the corresponding letters.
| A | B |
AT 4 
The oscillatory circuit capacitor is connected to a constant voltage source (see figure). Graphs A and B represent changes in physical quantities that characterize the oscillations in the circuit after switching switch K to position 2. Establish a correspondence between the graphs and physical quantities, the dependences of which on time these graphs can represent. For each position of the first column, select the corresponding position of the second and write down the selected numbers in the table under the corresponding letters.
| A | B |
Don't forget to transfer all answers to the answer sheet No. 1.
PART 3
Tasks C1-C6 are tasks, the full solution of which must be recorded in the answer sheet No. 2. It is recommended to carry out a preliminary solution on a draft. When filling out the solution in the answer sheet No. 2, first write down the task number (CI, C2, etc.), and then the solution to the corresponding problem. Write your answers clearly and legibly.
C1
The complete correct solution of each of the C2-C6 problems should include the laws and formulas, the application of which is necessary and sufficient to solve the problem, as well as mathematical transformations, calculations with a numerical answer and, if necessary, a figure explaining the solution.
C2 Washer mass m H m
C3 p1= 4 10 5 Pa. The distance from the bottom of the vessel to the piston is L S\u003d 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 \u003d 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 20 ohms and 150 ohms respectively. The resistance of the voltmeter is 10 kOhm, and the ammeter is 0.4 Ohm. The source emf 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 paper in physics
PART 1
For the correct answer to each task of part 1, 1 point is put. If two or more answers are given (including the correct one), an incorrect answer or no answer - 0 points.
job number | Answer | job number | 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 is made; for an incorrect answer (more than one error) or its absence - 0 points.
job number | Answer |
PART 3
CRITERIA FOR ASSESSING THE PERFORMANCE OF TASKS WITH A DETAILED ANSWER
C1 The figure shows an electrical circuit consisting of a galvanic cell, a rheostat, a transformer, an ammeter and a voltmeter. At the initial moment of time, the rheostat slider is set in the middle and is stationary. Based on the laws of electrodynamics, explain how the instrument readings will change in the process of moving the rheostat slider to the left. EMF of self-induction is neglected in comparison with ε.
Example of a possible solution |
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1. While moving the rheostat slider, the ammeter readings will gradually increase, and the voltmeter will register the voltage at the ends of the secondary winding. Note: A complete answer does not require an explanation of the instrument readings in the extreme left position. (When the engine comes to the extreme left position and its movement stops, the ammeter will show a constant current strength in the circuit, and the voltage measured by the voltmeter will be equal to zero.) 2. As the slider is moved to the left, the resistance of the circuit 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 the law of induction of Faraday, an EMF of induction arises | |
Points |
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A complete correct solution is given, including the correct answer (in this case, a change in instrument readings, item 1), and a complete correct explanation (in this case, items 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 with an indication of physical phenomena and laws, but an incorrect or incomplete answer is given; | 1 |
| 0 | |
where R is the resistance of the external circuit.
in the secondary winding, and consequently, the voltage U at its ends, recorded by a voltmeter.C2 Washer mass m starts moving along the chute AB from point A from a state of rest. Point A is located above point B at a height H= 6 m. In the process of moving along the chute, the mechanical energy of the washer decreases by ΔE = 2J due to friction. At point B, the puck flies out of the chute at an angle α = 15° to the horizon and falls to the ground at point D, which is on the same horizontal line as point B (see figure). BD = 4 m. Find the mass of the puck m. Ignore air resistance.
Example of a 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 BUT And IN taking into account friction losses:
From here: 2. Puck flight time from point IN exactly D:
reference with the origin at the point IN. 3. Flight range BD is determined from the expression for the horizontal coordinate 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 puck: Answer: m= 0.1 kg. |
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Criteria for assessing the performance of the assignment | Points |
A 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 the formulas of the kinematics of free fall); 2) the necessary mathematical transformations and calculations are carried out, leading to the correct numerical answer, and the answer is presented; in this case, the solution “in parts” (with intermediate calculations) is allowed. | |
| 2 |
Entries corresponding to one of the following cases are presented:
| 1 |
| 0 | |
where y- vertical coordinate of the puck in the system
C3 A monatomic ideal gas is contained in a horizontal cylindrical vessel closed by a piston. Initial gas pressure p 1 \u003d 4 10 5 Pa. The distance from the bottom of the vessel to the piston is L. Piston cross-sectional area S\u003d 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\u003d 10 cm. When the piston moves, a friction force of magnitude F tr \u003d 3 10 3 N. Find L. Assume that the vessel is in a vacuum.
Example of a possible solution |
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1. The piston will slowly move if the gas pressure force on the piston and the friction force from the side of the vessel walls balance each other: p 2 S = F tr,
2. Therefore, when the gas is heated, the piston will be stationary until the gas pressure reaches the value p 2. In this process, the gas receives an amount of heat Q 12. Q \u003d Q 12 + Q 23 \u003d (U 3 -U 1) + p 2 Sx \u003d (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 the performance of the assignment | Points |
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- an error has been made in the necessary mathematical transformations or calculations; | |
Entries corresponding to one of the following cases are presented: – Only provisions and formulas are presented that express physical laws, the application of which is necessary to solve the problem, without any transformations with their use, aimed at solving the problem, and the answer; | |
All cases of solution that do not match the above | |
in the initial state
C4 During laboratory work, the student assembled an electrical circuit according to the diagram in the figure. The resistances R 1 and R 2 are 20 ohms and 150 ohms, respectively. The resistance of the voltmeter is 10 kOhm, and the ammeter is 0.4 Ohm. The source emf 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 devices working or is one of them giving incorrect readings?
Example of a possible solution |
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To determine the current strength, we use Ohm's law for a complete circuit. Voltmeter and resistor R 1 are connected in parallel. Consequently, The ammeter shows a current strength of about 0.22 A. The division value of the ammeter scale is 0.02 A, which is more than the deviation of the readings from the calculation. Consequently, ammeter gives correct readings. From here U = I ⋅ R 1 \u003d 0.21 ⋅ 20 \u003d 4.2 (B). Voltmeter shows voltage |
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Criteria for assessing the performance of the assignment | Points |
A complete correct solution is given, including the following elements: 1) formulas are written correctly expressing the physical laws, the application of which is necessary to solve the problem in the chosen way (in this solution, Ohm's law for a complete circuit and for a circuit section, formulas for calculating the resistance of a circuit section with a series and parallel connection of conductors); 2) the necessary mathematical transformations and calculations are carried out, leading to the correct numerical answer, and the answer is presented. In this case, the solution "in parts" (with intermediate calculations) is allowed. | |
The presented solution contains paragraph 1 of the complete solution, but also has one of the following disadvantages: An error has been made in the necessary mathematical transformations or calculations; | |
Entries corresponding to one of the following cases are presented: Only provisions and formulas are presented that express the physical laws, the application of which is necessary to solve the problem, without any transformations with their use, aimed at solving the problem, and the answer; | |
All cases of decision 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 performs 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 an oscillating load 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.
Example of a possible solution |
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When the pendulum oscillates, the maximum speed of the load v can be determined from the law of conservation of energy: maximum lifting height. Maximum deflection angle where BUT- oscillation amplitude (displacement amplitude). From here Amplitude BUT 1 fluctuations in the displacement of the image of the load on the screen, located at a distance b from the plane of a thin lens, proportional to the amplitude BUT vibrations of a load moving at a distance but from lens plane: The distance a is determined by the thin lens formula: Consequently,
Answer: BUT 1 = 0.15 m. |
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Criteria for assessing the performance of the assignment | Points |
A complete correct solution is given, including the following elements: 1) the formulas expressing physical laws are correctly written down, the application of which is necessary to solve the problem in the chosen way (in this solution - the law of conservation of energy, the formula for increasing a thin lens and the formula for a thin lens); 2) the necessary mathematical transformations and calculations are carried out, leading to the correct numerical answer, and the answer is presented. In this case, the solution "in parts" (with intermediate calculations) is allowed. | |
The presented solution contains item 1 of the complete solution, but also has one of the following disadvantages: An error has been made in the necessary mathematical transformations or calculations; | |
Entries corresponding to one of the following cases are presented: Only provisions and formulas are presented that express the physical laws, the application of which is necessary to solve the problem, without any transformations with their use, aimed at solving the problem, and the answer; | |
All cases of solution that do not match the above | |
where 
C6 A monochromatic beam of parallel rays is created by a source that, in time Δ t= 8 10 -4 s emits N= 5 10 14 photons. Photons fall along the normal to the area S\u003d 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.
Example of a 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 the photon momentum: Expression for the radiation wavelength: |
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Criteria for assessing the performance of the assignment | Points |
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A complete correct solution is given, including the following elements: 1) formulas expressing physical laws are correctly written, the application of which is necessary to solve the problem by the chosen method (in this solution - formulas for light pressure, photon momentum, Newton's II law); 2) the necessary mathematical transformations and calculations are carried out, leading to the correct numerical answer, and the answer is presented. In this case, the solution "in parts" (with intermediate calculations) is allowed. | |||
The presented solution contains paragraph 1 of the complete solution, but also has one of the following disadvantages: An error has been made in the necessary mathematical transformations or calculations; | |||
Entries corresponding to one of the following cases are presented: Only provisions and formulas are presented that express the physical laws, the application of which is necessary to solve the problem, without any transformations with their use, aimed at solving the problem, and the answer; | |||
All cases of solution that do not match the above | |||
Test No. 18 Humidity and efficiency of a heat engine
Task 1. Steam pressure in the room at a temperature equal to 756 Pa. The saturation vapor pressure at the same temperature is 880 Pa. The relative humidity of the air is (round the answer to the nearest integer)
1) 1% 2) 60% 3) 86% 4) 100%
Task2. Saturated vapor pressure at temperature is 1.71 kPa. If the relative humidity of the air is 59%, then the partial vapor pressure at temperature is (choose the closest answer)
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 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 is isothermally compressed, reducing its volume by half. The 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 room air to the concentration of water molecules in saturated water vapor at the same temperature?
1) n less than 2.5 times 2) n more than 2.5 times 3) n less than 40% 4) n more than 40%
Task 7. What is the relative humidity of the air at a temperature if the dew point Saturated water vapor pressure 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: a dotted line - a graph of the dependence of the pressure of saturated water vapor on temperature, and a solid line - the process 1-2 of changing the partial pressure of water vapor.
As the partial pressure of water vapor changes, 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 30%. What will be the relative humidity if the volume of the vessel at a constant temperature is doubled?
1) 60% 2) 45% 3) 15% 4) 30%
Task 10. Relative humidity in a closed vessel 25%. What will be the relative humidity 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 air in a vessel closed by a piston is 30%. What will be the relative humidity if, by moving the piston, the volume of the vessel at a constant temperature is reduced by 3 times?
Task 12. Is such an ideal heat engine possible, which receives 50 J from the heater per cycle and performs useful work of 100 J? What is the efficiency of such a heat engine?
1) possible, 2) possible, 3) possible, 4) impossible,
Task 13. The temperature of the heat engine heater is 1000 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 refrigerator temperature. 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 performs 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 the 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 is more efficient?
1) the first one 2) the second one 3) both machines have the same efficiency 4) it is impossible to answer unambiguously
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 correct?
A. The work of the gas in the case of a cyclic process 1 → 2 → 3 → 4 → 1 is greater than the work of the 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 (s)?
A. A positive amount of heat cannot spontaneously transfer from a colder body to a hotter one.
B. It is impossible to create a cyclic heat engine, with the help of which it is possible to completely convert the energy received from the heater into mechanical work.
1) only A
2) only B
4) neither A nor B
Task 20. Which of the following statements is false(s)?
A. It is possible to transfer energy from a body with a lower temperature to a body with a higher temperature by doing work.
B. The efficiency of a cyclic heat engine is greater than 100%.
1) only A
2) only B