Verification work includes 18 tasks. Physics work takes 1 hour 30 minutes (90 minutes) to complete.

Read the list of concepts you encountered in your physics course.

Dynamometer, acceleration, pressure gauge, amperage, protractor, lens focal length.

Divide these concepts into two groups according to your chosen criterion. Write down the name of each group and the concepts in that group in the table.

Choose two correct statements about physical quantities or concepts. Circle their numbers.

1. Photons do not have rest mass and move in a vacuum with a speed equal to the speed of light in a vacuum.

2. X-ray radiation - electromagnetic waves, the energy of photons of which is greater than the energy of gamma radiation and less than the energy of ultraviolet radiation.

3. The oscillation period is the number of oscillations made by the oscillating body per unit of time.

4. Nuclear reaction is the process of interaction of an atomic nucleus with another nucleus or elementary particle, which may be accompanied by a change in the composition and structure of the nucleus.

5. The photoelectric effect is the emission of electrons by a substance under the influence of electromagnetic radiation (photons).

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While skating, the boy slipped and fell forward. What physical phenomenon caused him to fall forward instead of backward?

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Read the text and insert the missing words:

decreases

increases

does not change

The words in the answer may be repeated.

The rocket starts from the surface of the earth and moves upward with acceleration. We can say that with such a flight, the kinetic energy of the rocket is ________. The potential energy of the rocket is ________. Rocket momentum ________.

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increases, increases, increases

Perfect gas without getting off external source heat, does work 300 J. How much will its internal energy change in modulus?

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Using the fragment of the Periodic Table of Chemical Elements, shown in the figure, determine which particle is emitted which accompanies the radioactive transformation of the lead-187 nucleus into the mercury-183 nucleus.

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Alpha particles

The figure shows a diagram of Rutherford's experiment. A focused beam of alpha particles was directed onto a very thin sheet of gold foil. Some of the particles passed through the foil, other particles were deflected by a small angle, and some of the particles were rotated by 180 °. Explain this phenomenon. Explain the answer.

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A positively charged nucleus repels a positively charged particle

An electron flies into a uniform magnetic field perpendicular to the lines of magnetic induction. The magnetic field induction is 2.5 T. From the side of the magnetic field, a force of 1.6 10 -14 N begins to act on the electron. Calculate the value of the electron's velocity. Write down the formulas and make calculations.

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Possible answer

The Lorentz force is calculated by the formula F l = Bvq.

It follows that v = F l / Bq = 1.6 10 -14 N / (2.5 T 1.6 10 -19 C) = 4 10 4 m / s.

Arrange the types of electromagnetic waves emitted by the Sun in decreasing order of their wavelengths. Write down the corresponding sequence of numbers in the answer.

1) thermal radiation

2) X-rays

3) ultraviolet radiation

Answer: _____ → _____ → _____

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The departure time of the aircraft was measured using a clock. The hour scale is graduated in minutes. Determine the departure time of the aircraft, taking into account the measurement error, equal to the clock division. Write down in response the readings of the hours in hours, taking into account the measurement error.

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8.3 ± 0.2 hours

Examining the dependence of current strength on resistance, the student entered the voltmeter readings on a graph. If the error of the voltmeter is 0.5 V, and the resistance is 0.05 Ohm, then the current strength will be approximately equal.

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You need to investigate whether the current strength depends on the resistance at constant voltage. The following equipment is available (see picture):

Ammeter,

Voltmeter,

Power supply,

Connecting wires,

1 ohm, 2 ohm and 4 ohm resistor set

In response:

1. Draw an electrical circuit diagram consisting of a power supply, ammeter, rheostat, wire resistance and a key, connecting all devices in series. Connect a voltmeter to the wire resistance terminals to measure voltage.

2. Describe the procedure for conducting the research.

3. Make a conclusion.

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1. The circuit diagram is shown in the figure. The current in a circuit is defined as the ratio of the voltage on the conductor to the resistance of the conductor (according to Ohm's law for a section of the circuit).

2. Two or three measurements of currents and voltages are carried out.

3. The obtained values ​​of the resistances of the conductors are compared.

Establish a correspondence between the examples and the physical phenomena that are illustrated by these examples. For each example of the manifestation of physical phenomena from the first column, select the corresponding name of the physical phenomenon from the second column.

A) The puddle always seems less deep than it really is.

B) In a flat mirror, the right and left are swapped.

PHYSICAL PHENOMENA

1) Rectilinear light propagation in a homogeneous medium.

2) Refraction of light during the transition from one medium to another.

3) Mirror surfaces do not absorb light well.

4) Reflection of light from a smooth surface.

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Read the text and complete tasks 14 and 15.

How does electric welding work

When the electrode touches the junction of the parts to be welded, a breakdown of the air gap occurs and an electric arc is formed. At this moment, the welder needs, on the one hand, to move the heated tip of the electrode away from the metal part in order to avoid sticking, and on the other hand, to keep the distance between the electrode and the part to a minimum so that the arc is maintained.

Arc is a steady electrical discharge between the end of the electrode and the weld area of ​​the product. The temperature of the cathode region of the electrode exceeds 3000 degrees Celsius with a relatively small value of the potential difference - 20-25 V.

During welding, the electrode melts under the influence of high temperature. A drop of molten metal forms at the end of the electrode, which breaks off and is transferred to the metal of the item.

The transformer is the main element of the power source of the welding system. The specific operating conditions of the transformer require maximum power output at the time of welding. Welding transformers are designed to carry high currents. In household welding machines, currents reach 200 A.

What is the physical phenomenon underlying the action of electric arc welding?

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Melting metal at high temperatures in an electric arc.

Choose two correct statements from the list provided and write down the numbers under which they are indicated.

1) The temperature in the arc exceeds 3000 ° C.

2) Very high stress is generated during welding.

3) When welding, the electrode must touch the metal at all times.

4) Welding transformers differ from conventional ones in that they are designed to carry high currents.

5) During welding, the electrode melts the metal of the workpiece.

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Read the text and complete assignments 16-18.

Radiocarbon analysis

Radiocarbon analysis is a radioisotope dating method used to determine the age of biological remains, objects and materials of biological origin by measuring the content of the radioactive isotope 14 C in the material in relation to stable isotopes of carbon.

Carbon, which is one of the main constituents of biological organisms, is present in the earth's atmosphere in the form of several isotopes.

The 14 C isotope is radioactive, it is constantly formed mainly in the upper atmosphere at an altitude of 12-15 km and is subject to β-decay with a half-life of T 1/2 = 5730 years.

The ratio of radioactive and stable isotopes of carbon in the atmosphere and in the biosphere remains approximately the same due to the active mixing of the atmosphere, since all living organisms constantly participate in carbon exchange, receiving carbon from the environment. With the death of the organism, carbon exchange stops. After that, stable isotopes are preserved, and radioactive (14 C) gradually decays, as a result of which its content in the remains gradually decreases. Having determined the current ratio of isotopes in the biological material, it is possible to establish the time elapsed since the death of the organism.

To determine the age, carbon is released from a fragment of the sample under study (by burning a previously purified fragment). For the released carbon, the radioactivity is measured, on the basis of this, the isotope ratio is determined, which shows the age of the sample.

Measuring the age of an object by the radiocarbon method is possible only when the isotope ratio in the sample has not been violated during its existence, that is, the sample has not been contaminated with carbon-containing materials of a later or earlier origin, radioactive substances and has not been exposed to strong sources of radiation.

Cosmic ray intensity and solar activity;

Volcanic activity (carbon contained in volcanic discharges, “ancient”, practically does not contain 14 C);

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After about 11,460 years

Can radiocarbon dating be used to date samples from the past 200 years? Explain the answer.

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Possible answer: No. Samples of the past 200 years have been heavily contaminated with carbon isotopes from fuel combustion and atomic explosions. There will be big errors.

CONTEST

This article presents a device that is installed in the dashboard of a car and partly replaces the on-board computer.

I'll start with the background.
Once I put a torpedo from a foreign car in the car and realized that the speedometer terribly does not coincide with the real speed indicators. It was decided to put on-board computer. No sooner said than done. Many functions, etc., over time he refused, and had to do it myself.

From all the functions, I realized that I really only need a few basic ones, so I did.

On the Internet, I spied something separately and brought it all into the finished device presented below.
From the required readings, I chose: a voltmeter of the on-board network, a speedometer and an odometer (total mileage is not resettable, and daily, resettable).
Also, in my panel I did not show the standard indicator of the fuel level in the tank, I put the switch for the voltmeter readings, it shows either the voltage of the on-board network or the voltage drop across the tank sensor. The readings, of course, are not in liters, but in some numbers, so I remembered the readings of an empty tank, a quarter, a half, 0.75 tank, and a full one. And according to the readings, I can be guided by the amount of fuel in the tank.

Now about the scheme.

The voltmeter is assembled on a pic16f676 microcontroller, I used PNP transistors
Indicator with a common anode, with dynamic indication for three digits.
The speedometer-odometer uses a pic16f873a microprocessor, transistors operating on anodes, reverse conduction, an indicator for a three-digit speedometer with dynamic indication with a common anode, I took two indicators with OA with dynamics for the odometer.

Sensor Description :

The work algorithm is as follows:
The voltage of 12 volts from the battery is always supplied to the circuit, but from the ignition switch 15/1 it is supplied to the circuit as power, and to the 21 MK leg, and when the ignition is turned off, the circuit does not immediately de-energize, but data on the mileage is recorded in EEPROM of the controller, when the recording was successful, the microcontroller gives a command to the keys that remove the supply voltage of the entire circuit. During recording, the odometer indicator lights up the inscription "record"
V printed circuit board there is a switch that either supplies power directly to the anodes of the speedometer, or passes it through a resistor, which in turn, at night, "mutes" the brightness of the glow, so as not to dazzle, but whoever does not need it, you can put a jumper on the board. (which I did at home)
When you turn the ignition key, the voltmeter, speedometer and total mileage readings light up, to switch to the daily mileage, you must briefly press the reset button, And to reset the daily mileage, you must hold the same button for a long time, and the word "reset" will appear on the indicator
The circuit works on my machine, and already on a friend's machine. So the circuit is fully operational and tested in the field.
And yet, in the voltmeter, instead of a trimming resistor, I put a constant 13 kOhm (in my case) so that the readings do not get lost under the influence of vibration.
And yet, the photo shows the board from the first experiment, the tracks are not completed there, but you are presented with a completely finished board, with all the changes.

Photo of the finished device

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1 watt per centimeter per degree Celsius [W / (cm · ° C)] = 0.1 kilowatt per meter per kelvin [kW / (m · K)]

Initial value

Converted value

watt per meter per kelvin watt per centimeter per degree Celsius kilowatts per meter per kelvin calorie (IT) per second per centimeter per degree Celsius calorie (therm) per second per centimeter per degree Celsius kilocalorie (IT) per hour per meter per degree Celsius kilocalorie (therm.) per hour per meter per degree Celsius BTU (M) inches per second per sq. foot per deg. Fahrenheit BTU (T) inches per second per sq. foot per deg. Fahrenheit BTU (M) ft per hour per sq. foot per deg. Fahrenheit BTU (T) feet per hour per sq. foot per deg. Fahrenheit BTU (M) inches per hour per sq. foot per deg. Fahrenheit BTU (T) inches per hour per sq. foot per deg. Fahrenheit

Ferromagnetic liquids

More about thermal conductivity

General information

Thermal conductivity is the property of bodies to redistribute heat from more heated parts to less heated ones. This property does not depend on body size, but depends on temperature. The higher the thermal conductivity of a substance, the better heat is transferred through it. For example, wool has a lower thermal conductivity than metal, so if a child touches his mitten with his tongue in winter, then nothing will happen to him. If he decides to taste the metal doorknob, the moisture on his tongue will freeze and his tongue will freeze.

Thermal conductivity has many uses in technology and everyday life. It is thanks to her that it is possible to regulate the body temperature of people and animals, cook food, and provide comfort in the house, even if the weather is bad.

Application of thermal conductivity

Thermal conductivity in the kitchen

Thermal conductivity and its regulation are important in the cooking process. Often during the heat treatment of the product, it is necessary to maintain a high temperature, therefore, metals are used in the kitchen, since their thermal conductivity and strength are higher than that of other materials. Pots, pans, baking trays, and other utensils are made of metal. When they come into contact with a heat source, this heat is easily transferred to food. Sometimes it is necessary to reduce the thermal conductivity - in this case, pots made of materials with a lower thermal conductivity are used, or they are prepared in ways that transfer less heat to the food. Cooking in a water bath is one example of a decrease in thermal conductivity. Usually, a saucepan over a fire is poured into water, in which a second pan of food is placed. The temperature here is controlled due to the lower thermal conductivity of the water and due to the fact that the heating temperature of the inner pot does not exceed the boiling point of the water, that is, 100 ° C (212 ° F). This method is often used with foods that burn easily or that cannot be boiled, such as chocolate.

Metals that conduct heat very well are copper and aluminum. Copper is more thermally conductive, but also more expensive. Pots are made from both metals, but some foods, especially acidic ones, react with these metals and produce a metallic taste. Such pots, especially copper ones, require careful maintenance, therefore, in the kitchen, they often use cheaper and more convenient stainless steel pots to handle and maintain.

The requirements for thermal conductivity depend on how the food is cooked and on the flavor and consistency that the chef wants to achieve. For example, cooking usually requires a lower thermal conductivity than frying. Thermal conductivity is regulated by choosing different dishes, as well as using products with a higher or lower liquid content. For example, the amount of oil in the bottom of a pot or pan affects thermal conductivity, as does the total amount of liquid in a food.

For utensils intended for cooking, materials with high thermal conductivity are not always used. In the oven, for example, ceramic cookware is often used, the thermal conductivity of which is much lower than that of metal cookware. Their main advantage is their ability to keep the temperature.

A good example of the use of materials with high thermal conductivity in the kitchen is the stove. For example, the burners of an electric stove are made of metal to ensure good heat transfer from the hot coil of the heating element to the pot or frying pan.

People use materials with low thermal conductivity between hands and utensils to avoid scalding. Many saucepans have plastic handles, and pans are removed from the oven with oven mitts made of cloth or low thermal conductivity plastic.

Low thermal conductivity materials are also used to keep food temperatures constant. So, for example, to keep your morning coffee or soup, which is taken on a trip or for lunch to work, hot, it is poured into a thermos, cup or jar with good thermal insulation. Most often, food remains hot (or cold) in them due to the fact that there is a material between their walls that does not conduct heat well. This can be polystyrene or air, which is in the closed space between the walls of the vessel. It prevents heat from passing into the environment, food from cooling, and hands from getting burned. Styrofoam is also used for cups and containers for takeaway food. In a vacuum Dewar (known as a "thermos", by the name brand) there is almost no air between the outer and inner walls - this further reduces the thermal conductivity.

Thermal conductivity for heat

We use materials with low thermal conductivity to maintain a constant body temperature. Examples of such materials are wool, down, and synthetic wool. The skin of animals is covered with fur, and birds - with low thermal conductivity, and we borrow these materials from animals or create synthetic fabrics similar to them, and from them we make clothes and shoes that protect us from the cold. In addition, we make blankets, as it is more comfortable to sleep under them than in clothes. In addition, the body temperature drops during sleep, and we need additional insulation. Sometimes a blanket is not enough because it is not attached to the sheets, and through the cracks that form when we roll over in our sleep, heat can escape and cold air can leak out.

Air has low thermal conductivity, but the problem with cold air is that it can usually move freely in any direction. It displaces the warm air around us, and we get cold. If the movement of air is limited, for example, by enclosing it between the outer and inner walls of the vessel, then it provides good thermal insulation. Animals use air to improve the insulation of their bodies. For example, birds sit crumpled in cold weather to add a layer of air inside their plumage. This air hardly moves, therefore it insulates well from the cold. We also have this mechanism - if we are cold, then we have "goose bumps". If in the process of evolution we did not lose our fur, then such "coughing" would help us to keep warm.

Snow and ice also have low thermal conductivity, so people, animals and plants use them for thermal insulation. There is air inside fresh, un-compacted snow, which further reduces its thermal conductivity, especially because the thermal conductivity of air is lower than the thermal conductivity of snow. Thanks to these properties, the ice and snow cover protects the plants from freezing. Animals dig holes and whole caves for wintering in the snow. Travelers crossing the snow-covered areas sometimes dig these caves to spend the night in them. Since ancient times, people have been building shelters of ice, and now they are creating entire entertainment centers and hotels. Fire often burns in them, and people sleep in furs and synthetic sleeping bags. The guests say that they were very warm and comfortable all night long, although it is not recommended to get up in the middle of the night to use the toilet. Due to the low thermal conductivity of ice, candlesticks are sometimes made from it, and you can find many workshops on how to make them on the Internet.

Maintaining body temperature in humans and animals

To ensure normal life in the body of humans and animals, it is necessary to maintain a certain temperature within very narrow limits. Blood and other fluids, as well as tissues, have different thermal conductivity and can be adjusted depending on the needs and ambient temperature. For example, the body can change the amount of blood in an area of ​​the body or throughout the body by expanding or narrowing blood vessels. Our body can also thicken and thin the blood. In this case, the thermal conductivity of the blood, and, consequently, the part of the body where this blood flows, changes.

Other applications

Many people like to relax in saunas or baths, but it would be impossible to sit there on benches made of material with high thermal conductivity. It takes a long time to equalize the temperature of such materials with the body temperature, so materials with low thermal conductivity are used instead, such as wood, the upper layers of which take on body temperature much faster. Because the temperature rises high enough in the sauna, people often wear wool or felt hats over their heads to protect them from the heat. In Turkish baths, hamams, the temperature is much lower, so there they use a material with a higher thermal conductivity for benches - stone.

Some places for swimming, such as the onsen hot springs in Japan, are outside. The human body is well insulated with fat, which has a low thermal conductivity, so people can relax and enjoy a hot bath even if it's freezing outside. Humans are not the only creatures to appreciate this feature of the body. Macaques are also very fond of swimming in hot springs in winter.

Thermal conductivity of some materials

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I tried to put together a digital speedometer and tachometer with a 7-segment display, but nothing came of it. the circuit was too complex. Later I made a tachometer with LEDs. Then I purchased a stepper motor, used it as a speed sensor and built an LED speedometer.

But I've always thought about a 7-segment multimeter. It can be built on programmable PICs, but unfortunately I do not understand this. Then I remembered the ICL7107, a simple and reliable analog-to-digital converter (ADC) used in digital voltmeters.

VOLTMETER? Why not put together a voltmeter and then calibrate it so that it shows the vehicle speed from a speed sensor (stepper motor)? And take the voltage for the tachometer at the output of the LM2917? Why not add a digital thermometer using the LM35 temperature sensor?

Digital voltmeter circuit

I started with the main circuit (ICL7107 voltmeter). The ICL7107 is an analog-to-digital converter interfaced with a seven segment display.

The “-5V” power supply is obtained from the 7660 chip from the “+ 5V” input voltage, although “-5V” can also be obtained using the 7905 voltage regulator from + 12V. To this are added the other few components.

Power Supply

The + 12V voltage from the battery is converted to "+ 5V" using a 7805 voltage regulator, two non-polar 100nF capacitors, one 470uF electrolytic capacitor and rectifier diode 1N4007.

Speed ​​signal

A stepper motor was previously attached to the transmission of my car. Generated current stepper motor variable, so I added a diode bridge at 1N4007 and 100nF for smoothing the output. Added 1.5mΩ and 470kΩ potentiometer for calibration.

Tachometer signal

The LM2917 microcircuit is a frequency-voltage converter. It converts the engine speed signal from the ignition coil into a voltage (high input voltage !!!).

The voltage corresponding to the revolutions is removed from terminals 5 and 10. Calibration via 220K trimmer. Powered by the same + 5V source.

Temperature signal

I used an LM35 digital temperature sensor. It has an accuracy of 0.5 degrees, a sensitivity of 10mV / degree. The LM35DZ variant has an operating range of only 0-100 degrees (Celsius), and the LM35AH from -55 to 150 degrees. The sensor is also powered by + 5V. After connecting the wires, I filled them with epoxy.

The resin is non-conductive and will provide an airtight seal. I used a 100k ohm potentiometer for calibration. I put the LM35 sensor under my tongue, waited a little and set the potentiometer to 37 degrees on the display (do we think I had a normal body temperature?) Then I put it in boiling water and calibrated to 100 degrees.

The sensor must be well attached to the motor housing to display the correct temperature. I drilled a small recess in the body (steel), inserted the sensor and filled it with epoxy.
You may prefer to use such a sensor to measure the coolant temperature. In the future, I will add 2 more sensors, one for measuring the outside temperature and one for the temperature inside the car.

Display readout switching

I used a simple 6-position rotary switch. Currently I only use 3 positions (speed, tachometer and engine temperature).

The switch is installed in the place of the old potentiometer (used to adjust the brightness of the dashboard backlight).

And I also want to note one point, if you decide to buy a truck, crane or other special equipment, then I want to recommend you an excellent company that does just that. Come in, see and choose, trucks are always available, both new and used.