In accordance with this task, the subsection “Elements of Astrophysics” of the section “ The quantum physics and elements of astrophysics”, including the following points:
- solar system: terrestrial planets and giant planets, small bodies of the solar system.
- Stars: a variety of stellar characteristics and their patterns. Sources of star energy.
- Modern ideas about the origin and evolution of the Sun and stars.
- Our Galaxy. Other galaxies. Spatial scales of the observable Universe.
- Modern views on the structure and evolution of the Universe.
Several tasks of the first part, which have a modified format, deserve special attention: a prototype has appeared 13 tasks to electrostatics with the choice of the direction of acceleration (force) acting on the charge. That is, now a particle or a conductor with a current in a magnetic field is not the only task with choosing a direction and writing a word(s) in response.
The negative charge -q is in the field of two stationary charges: positive +Q and negative -Q (see figure). Where is the acceleration of charge -q directed relative to the figure (to the right, left, up, down, towards the observer, away from the observer) at this moment in time, if only charges +Q and -Q act on it. Write your answer in word(s).
Answer: ______________________ .
Got another change Exam position 23. A prototype of the task has been added, in which you do not need to select two elements that differ only in a variable in the task condition, but rather completely assemble a setup for conducting the experiment.
It is necessary to assemble an experimental setup that can be used to determine the coefficient of sliding friction between steel and wood. To do this, the student took a steel bar with a hook. Which two additional items from the list of equipment below must be used to conduct this experiment?
In response, write down the two selected items.
Now on 30 exam positions You can expect a problem with saturated vapor and humidity. The difference between this task is a characteristic called
"Humidification performance." An example of such a task is below
In a room measuring 4x5x3 m, in which the air has a temperature of 10°C and a relative humidity of 30%, an air humidifier with a capacity of 0.2 l/h was turned on. What will the relative humidity in the room be after 1.5 hours? The pressure of saturated water vapor at a temperature of 10°C is 1.23 kPa. Consider the room to be a sealed vessel.
At the 14th position of the exam, there can now be tasks that test knowledge of topics
"The Law of Conservation electric charge" and "Capacitor"
IN task 18 exam positions (establishing correspondence between graphs and physical quantities, between physical quantities and formulas) added service station basics.
The evaluation criteria for the first and second parts, as well as the maximum number of primary points and their distribution, have been changed:
Good luck!
You will find a lot of interesting information about preparing for exams in our group on VKontakte.
Part 1
2. Two athletes different masses on identical cars moving at speeds of 10 km/h and 20 km/h, respectively, they began to brake, blocking the wheels. What is the ratio S 1 /S 2 braking distances of their cars with the same coefficient of wheel friction on the ground?
Answer: _______.
3. The body has a kinetic energy of 100 J and an impulse of 40 (kgm)/s. What is the body mass?
Answer: _______.
4. A pendulum 1 m long made 60 oscillations in 2 minutes. Find the acceleration free fall for a given area. Round your answer to the nearest hundredth.
Answer: _______m/s 2.
- Projection a x acceleration of body 1 is less than projection a x body acceleration 2.
- Projection a x acceleration of body 1 is 0.6 m/s 2 .
- Body 1 at time 0s was at the beginning of the countdown.
- At time 15 s, body 2 changed the direction of its movement.
- Projection a x acceleration of body 2 is 0.2 m/s 2 .
Answer: |
6. A load suspended from a dynamometer is lowered at a constant speed into a glass partially filled with water until the load is completely immersed (see figure). How do the elastic force exerted by the spring and the Archimedes force acting on the load change during immersion? Establish a correspondence between physical quantities and their possible changes. For each quantity, determine the corresponding nature of the change:
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7. Body thrown with speed v at an angle α to the horizontal, over time t rises to maximum height h above the horizon. Air resistance is negligible.
Establish a correspondence between physical quantities and formulas by which they can be determined.
to the table selected numbers.
PHYSICAL QUANTITIES A) rise time t to maximum height B) maximum height h above the horizon | FORMULAS |
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Answer: | |||
No. 8. Pressure 10 5 Pa is created by gas molecules whose mass is 3 10-26 kg at a concentration of 10 25 m -3 . What is the root mean square speed of molecules?
Answer:________m/s.
9 . Useful work of an ideal heat engine per cycle is 30J, while the machine transfers 120J to the refrigerator. What is the efficiency of a heat engine?
Answer:________%
10. The figure shows a graph of temperature versus time for the heating process of a 1 kg lead ingot. How much heat did the lead receive during 15 minutes of heating? Answer: ________J. | ||||
11. The figure shows an experimentally obtained graph of temperature versus time when heating a certain substance. Initially, the substance was in a liquid state. Select from the list provided two true statements. 1) The boiling point is 100°C. 2) Heat capacities in liquid and gaseous state are the same. 3) A substance has the greatest internal energy at a point D. 4) A substance has the least internal energy at a point B. 5) At point D the substance is in a gaseous state.
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12. Internal energyν moles of a monatomic ideal gas is equal to U. The gas occupies a volume V. R is the universal gas constant. What are the pressure and temperature of the gas? 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.
Formula
13. Electron e , flying into the gap between the poles of an electromagnet, has a horizontal speed, which is perpendicular to the induction vectormagnetic field directed horizontally (see figure). How directed(right, left, up, down, towards the observer, away from the observer)Lorentz force acting on an electron.Write your answer in word(s). Answer: __________. |
14. A capacitor with an electrical capacity of 1F was charged to a voltage of 6V. Then an uncharged capacitor with an electrical capacity of 1F was connected to it in parallel. What is the energy of a system of two capacitors after they are connected? (Give your answer in joules).
Answer: _______J.
15. When a ray of light passes from one medium to another, the angle of incidence is 30 0 , and the angle of refraction is 60 0 . What is the relative index of refraction of the first medium relative to the second? (Round your answer to the nearest hundredth.)
Answer:_______.
16. A point source of light is located in a container with liquid and descends vertically down from the surface of the liquid. In this case, a spot appears on the surface of the liquid, formed by rays of light emerging from the liquid into the air. The immersion depth of the source (the distance from the surface of the liquid to the light source), measured at regular intervals, as well as the corresponding bright spot radius are presented in the table. The error in measuring the immersion depth and spot radius was 1 cm. Choose two correct statements based on the data given in the table.
Immersion depth, cm | |||||||
Spot radius, cm |
Answer |
17. A small object is located on the main optical axis of a collecting lens at triple focal length from it. They begin to bring it closer to the focus of the lens. How do the distance from the lens to the image and the optical power of the lens change?
For each quantity, determine the corresponding pattern of change.
1) increases
2) decreases
3) does not change
Write down the selected numbers for each physical quantity in the table. The numbers in the answer may be repeated.
18. A beam of light passes from air into glass. Light wave frequency ν, speed of light in air With, refractive index of glass relative to air n . Establish a correspondence between physical quantities and combinations of other quantities by which they can be calculated.
For each position in the first column, select the corresponding position in the second and write down V table of selected numbers under the corresponding letters.
Answer: | ||
19. Specify mass and charge number of the particle that causes nuclear reaction +…→ +
20. A sample of radioactive radium is in a closed vessel from which the air has been evacuated. Radium nuclei undergo α decay with a half-life of 11.4 days. Determine the number of moles of helium in the vessel after 22.8 days if the sample at the time of placement contained 2.4 * 10 23 radium atoms.
Answer: _______mol.
21. Establish a correspondence between physical quantities and formulas by which they can be calculated (ν - photon frequency, ћ - Planck’s constant, p - photon momentum). To each position of the first columnselect the corresponding position of the second and write down the selected numbers in the table under the corresponding letters.
Answer: | |||
22. A student, studying the laws of geometric optics, conducted an experiment on the refraction of light, directing a narrow beam from the left onto a glass plate (see photograph). The error in measuring the angles of incidence and refraction is equal to half the division value of the protractor. What is the angle of refraction based on these measurements? Write down your answer taking into account the measurement error. Answer: (______±______) |
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23. It is necessary to assemble an experimental setup, with the help of which you want to determine the resistance of a light bulb. To do this, the student took connecting wires, a rheostat, a key, a battery and a voltmeter. Which two items from the list of equipment below must be additionally used to conduct this experiment?
- Bulb
- Ammeter
- Resistor
- Voltmeter
- Battery
In your answer, write down the numbers of the selected equipment.
Answer: |
24. Two identical plasticine balls collided, and their velocity vectors immediately before the collision were mutually perpendicular and differed twice in magnitude: v 1 =2 v 2 . What was the speed of the slower ball before the absolutely inelastic collision, if after it the speed of the balls became equal to 1.5 m/s? Round your answer to tenths.
Answer: ____________m/s.
25. In a calorimeter, 50g of water and 5g of ice are in thermal equilibrium. What should be the minimum mass of a bolt having specific heat capacity 500 J/(kg*K) and a temperature of 330K, so that after lowering it into the calorimeter, all the ice will melt? Neglect heat losses.
Answer_______kg.
26. In two ideal oscillatory circuits with the same inductance, free electromagnetic oscillations occur, and the period of oscillation in the first circuit is 9 10 -8 s, in the second 3 10 -8 With. How many times is the amplitude value of the current in the second circuit greater than in the first, if the maximum charge of the capacitor is the same in both cases?
Answer: _______times.
How did the saturation photocurrent change (decreased or increased)? Explain why the saturation photocurrent changes, and indicate what physical laws you used to explain.
28. On a thread that can withstand a tension force of 40 N, a boy uniformly rotates a stone of mass 1 kg in vertical plane. The center of rotation is at a height of 4 m, the radius of the circle described by the stone is 1 m. At what angular velocity must the boy rotate the stone so that the thread does not break? At what distance from the boy will the stone fall?
30. How much electricity must be consumed to produce 5 liters of hydrogen at a temperature of 20 0 C and a pressure of 120 kPa, if electrolysis is carried out at a voltage of 10 V, and the efficiency of the installation is 75%?
31. Suppose that the diagram of the lower energy levels of atoms of a certain element has the form shown in Fig., and the atoms are in a state with energy E(1) . An electron, colliding with one of these atoms at rest, received some extra energy. The momentum of an electron after a collision with an atom turned out to be equal to 1.2 × 10-24 kg×m/s. Determine the kinetic energy of the electron before the collision. Neglect the possibility of an atom emitting light when colliding with an electron. Neglect the recoil effect. |
System for assessing the performance of individual tasks and exams
work in general
A short answer task is considered completed if the written
in form No. 1 the answer coincides with the correct answer. Tasks 1–4, 8–10, 13–15, 19, 20, 22 and 23 of Part 1 and tasks 24–26 of Part 2 are scored 1 point.
Tasks 5–7, 11, 12, 16–18 and 21 of Part 1 are worth 2 points if correct
both response elements are indicated; 1 point if there is an error in the instructions
one of the answer elements, and 0 points if two errors were made.
Job No. | Answer |
0.25 |
|
9,86 |
|
45 or 54 |
|
1000 |
|
39000 |
|
up |
|
13or31 |
|
20,00,5 |
|
12 or 21 |
|
0,058 |
|
Option
№ 27
1. The saturation photocurrent will increase.
2. Since light travels behind the lens in a parallel beam, the point source of light is at the front focus of the lens.
3. Therefore, in the case of a lens with a shorter focal length, the light source is at a smaller distance from the lens (see figure).
4. As a result, photons hitting the second lens close to its edge (in the right figure this is the area from the dotted line to the edge of the lens) do not hit the first lens. Therefore, the number of photons incident on the second lens per unit time is greater than those incident on the first.
5. The saturation photocurrent is proportional to the number of photons incident on the photocathode per unit time. In the proposed installation, all photons that pass through the lens fall on the photocathode, so the saturation photocurrent when using the second lens will be greater than in the first case.
№ 28.
Sample possible solution:
The thread experiences the greatest tension when the stone passes the lowest point of the circle. The equation for Newton's second law for this moment is:
T- mg = Hence the angular velocity at which the thread will break: ω =. The speed of the stone at the moment of separation will be directed horizontally and equal in magnitude to ν =.
Stone flight range- time of free fall from height; from here: .
Substituting the data, we get
Answer: ,
№29
№ 30.
According to Faraday's law,, Where – molar mass atomic hydrogen(=0.001 kg/mol, n - valence of hydrogen (n=1), F-Faraday number. Installation efficiency. Let us write the equation for the state for hydrogen:, Where – molar mass of molecular hydrogen equal to 0.002 kg/mol. Solving the resulting system of equations, we find.
Answer: .
Faraday number
№ 31
If, during a collision with an atom, an electron gains energy, then the atom goes into state E(0) . Consequently, after the collision, the kinetic energy of the electron became equal to E=E 0 +3.5 eV, where E 0 - electron energy before collision; from here:E 0 =E-3.5 eV. Impulse p electron is related to its kinetic energy by the relation p 2 =m 2 ν 2 =2mE, or , where m - electron mass.
Hence .
Answer
Solving tasks No. 23 may require knowledge basic concepts from different branches of physics - mechanics, electrodynamics, etc. They are described in theoretical sections to the corresponding tasks. What unites tasks No. 23 is that they are related to conducting physical experiments. Therefore, in in this case it is necessary to have a good understanding of what devices, instruments and available means are usually used for this. Some of them are familiar to any person - a ruler, a beaker, etc. Others that require an understanding of complex physical phenomena are described in the theory section.
Theory for task No. 23 of the Unified State Exam in Physics
Oscillatory circuit
An oscillatory circuit is a closed electrical circuit, in the simplest case it includes a coil and a charged capacitor connected in series. Such a circuit provides free electromagnetic oscillations that occur in the coil due to the transfer of charge from the capacitor plates. This process represents the mutual transformation of the electric field of the capacitor into the magnetic field of the coil and vice versa.
In practice, the oscillatory circuit includes a current source, and may also additionally contain resistors (resistances), measuring instruments and etc.
Capacitor
The capacitor is used to conduct experiments related to polarization processes, the study of dielectric media, their interaction with charged bodies, etc. A capacitor is a device consisting of a pair of conductor plates and a small (compared to the area of the plates) dielectric layer between them.
Using a capacitor, the dynamics of changes in the series are calculated and observed physical quantities– electrical capacity, electric field voltage, charge, etc.
Inductor
A coil is an insulated conductor rolled into a spiral. There may be a core (magnetic or non-magnetic) inside the spiral. The device is characterized by inductance (L), characterized by low resistance to the electric current passing through the coil and low capacitance.
Analysis of typical options for tasks No. 23 of the Unified State Exam in Physics
Demo version 2018
It is necessary to assemble an experimental setup that can be used to determine the coefficient of sliding friction between steel and wood. To do this, the student took a steel bar with a hook. Which two additional items from the list of equipment below must be used to conduct this experiment?
- wooden slats
- dynamometer
- beaker
- plastic rail
- ruler
In response, write down the numbers of the selected items.
Solution algorithm:
- We write down a formula that can be used to calculate the friction force. We determine the quantities on which the friction coefficient depends.
- We determine the list of equipment necessary to study the friction force and find the slip coefficient.
- We analyze the list of equipment proposed in the conditions for its necessity in this experiment. We find two items that need to be supplemented with the installation.
- We write down the answer.
Solution:
First option (Demidova, No. 2)
The student needs to experimentally identify the dependence of the electrical capacity of a flat capacitor on the distance between its plates. In all the figures below, S is the area of the capacitor plates, d is the distance between the capacitor plates, ε is the dielectric constant of the medium filling the space between the plates. Which two capacitors should be used to conduct such a study?
Solution algorithm:
- We write down the formula for the capacitance of a flat-plate capacitor.
- To clarify the dependence, we analyze the relationship between the change in capacitance of the capacitor depending on the change in its parameters. We determine the dependent quantities.
- Analyzing the proposed answers, we find a pair of capacitors that meet the specified criteria.
- We write down the answer.
Solution:
Second option (Demidova, No. 5)
It is necessary to discover the dependence of the frequency of free electromagnetic oscillations in the oscillatory circuit on the inductance of the coil. Which two oscillatory circuits should be chosen to conduct such an experiment?
Write down the numbers of oscillatory circuits in the table.
Solution algorithm:
- We write down the formula for the oscillation frequency.
- We analyze the formula and determine the required contour parameters. We find a pair of corresponding contours among the drawings.
- We write down the answer.
Solution:
1. In the simplest circuit, the frequency ω of free oscillations can be determined using a formula relating this quantity to their period and Thomson’s formula. We get:
.
(2) → (1): 
.
2. From the derived formula it is clear that to determine the dependence of the oscillation frequency on the inductance, two circuits with coils of different inductance and capacitors of the same capacitance are needed. This condition corresponds to contours numbered 1 and number 4.
Third option (Demidova, No. 11)
The student studies Archimedes' law by changing in experiments the volume of a body immersed in a liquid and the density of the liquid. Which two experiments should he choose to discover the dependence of the Archimedean force on the volume of the immersed body? (The figures indicate the density of the liquid.)
Record the numbers of the selected settings in the table.
Solution algorithm:
- We write down the formula of Archimedes' law.
- Let's study the dependence of the Archimedes force on the volume of the body.
- We write down the answer.
Solution:
- Archimedes' principle is expressed as the formula: F A =ρgV.
- Since g=const, then F A depends on the volume V of the body and the density ρ of the medium. If you want to find the dependence specifically on volume (V), then in different experiments only its value should change. Those. the medium must be the same, which means: the liquids in two experiments must have the same density (ρ). The experiments in Figure 3 and Figure 4 correspond to this condition.
The figure shows the Hertzsprung–Russell diagram.
Select two statements about the stars that correspond to the diagram.
A block with a mass of 0.7 kg moves from rest along a horizontal table, connected to a load with a mass of 0.3 kg by a weightless, inextensible thread thrown over a smooth weightless block (see figure). The coefficient of friction between the block and the table surface is 0.2. Determine the acceleration of the block.
Answer: ___________________________ m/s 2 .
The red boundary of the photoelectric effect of the metal under study corresponds to the wavelength lcr = 600 nm. What is the wavelength of light that knocks out photoelectrons, whose maximum kinetic energy is 3 times less than the energy of incident photons?
Answer: ___________________________ nm
Do not forget to transfer all answers to answer form No. 1 in accordance with the instructions for completing the work.
To record answers to tasks 27–31, use ANSWER FORM No. 2. First write down the task number (27, 28, etc.), and then the solution to the corresponding problem. Write down your answers clearly and legibly.
| 28 |
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 .
Complete correct solution each of problems 28–31 should contain 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.
A horizontal tube of constant cross-section, sealed at one end, contains a column of mercury 7.5 cm long, which separates the air in the tube from the atmosphere. The tube was placed vertically, with the sealed end down. How many degrees should the air in the tube be heated so that the volume occupied by the air remains the same? The air temperature in the laboratory is 300 K, and Atmosphere pressure is 750 mmHg. Art.
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Main optical axis of a thin converging lens with focal length F= 20 cm and point light source S are in the plane of the drawing. Dot S is at a distance b= 60 cm from the plane of the lens and at a distance H from its main optical axis.
In the left focal plane of the lens lies a thin opaque screen with a small hole A, located in the drawing plane at a distance h= 4 cm from the main optical axis of the lens. Having passed through the hole in the screen and the lens, the beam S.A. from a point source intersects its main optical axis at a distance
x=16 cm from the plane of the lens. Find the value H. Neglect light diffraction. Construct a drawing showing the path of the ray through the lens.
