Home experimental tasks in physics. Experiment in physics

The paper presents recommendations, in the form of algorithms, for organizing experiments conducted by the students themselves in the classroom with answers, outside the school on the teacher's homework; on the organization of short-term and long-term observations of natural phenomena, tasks of an inventive nature for the creation of equipment for experiments, operating models of machines and mechanisms carried out by students at home on special tasks of the teacher, the types of physical experiments are also systematized in the work, examples of experimental tasks for different topics and sections of physics grades 7-9.

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municipal competition

socially significant pedagogical innovations in the field of

general, preschool and additional education

municipality of the resort city of Gelendzhik

organization of experimental work

in physics lessons and outside of school hours.

physics and mathematics teacher

MAOU secondary school №12

resort city of Gelendzhik

Krasnodar Territory

Gelendzhik - 2015

Introduction …………………………………………………………………….....3

1.1 Types of physical experiments.……….. …………………………..5

2.1 Algorithm for creating experimental tasks…….……………..8

2.2 Results of testing experimental tasks in grades 7-9 .............................................................. ................................................. ...................10

Conclusion …………………………………………………………………...12

Literature …………………………………………………………………....13

Appendix………………………………………………………………….14

4. Lesson in the 8th grade on the topic "Serial and parallel

Connection of conductors.

"The joy of seeing and understanding is the most beautiful gift of nature."

Albert Einstein

Introduction

In accordance with the new requirements of the state educational standard, the methodological basis of education is a system-activity approach that allows students to form universal learning activities, among which an important place is occupied by the acquisition of experience in the application of scientific methods of cognition, the formation of experimental work skills.

One of the ways to connect theory with practice is to set up experimental tasks, the solution of which shows students the laws in action, reveals the objectivity of the laws of nature, their obligatory implementation, shows the use by people of knowledge of the laws of nature to predict phenomena and control them, the importance of studying them to achieve specific, practical purposes. Especially valuable should be recognized such experimental problems, the data for the solution of which are taken from the experience that takes place before the eyes of the students, and the correctness of the solution is checked by experience or a control device. In this case, the theoretical principles studied in the course of physics acquire special significance in the eyes of students. It is one thing to come to some conclusions and their mathematical formulation through reasoning and experiment, i.e. to a formula that will have to be learned by heart and be able to deduce, and limit yourself to this, another thing is to be able to manage them on the basis of these conclusions and formulas.

Relevance innovation is due to the fact that the organization of educational work should be set in such a way that it affects personal sphere children, and the teacher would create new forms of work. The creative direction of work brings the teacher and the student together, activates the cognitive activity of the participants in the educational process.

The paper presents recommendations in the form of algorithms for organizing experiments conducted by the students themselves in the classroom when answering, outside the school on the teacher's homework; on the organization of observations of short-term and long-term natural phenomena, tasks of an inventive nature for the creation of equipment for experiments, operating models of machines and mechanisms carried out by students at home on special tasks of the teacher, the types of physical experiments are also systematized in the work, examples of experimental tasks on various topics and sections are given physics grades 7-9. The following materials were used in the work, which present physical experiments used in the work on projects, during learning activities and after hours:

Burov V.

Mansvetova G.P., Gudkova V.F.Physical experiment at school. From work experience. A guide for teachers. Issue 6 / - M .: Education, 1981. - 192s., Ill., as well as materials from the Internethttp://kopilkaurokov.ru/ , http://www.metod-kopilka.ru/ ,

When analyzing similar products existing in Russia have been revealed: in physics, and in the education system as a whole, there have been big changes. The emergence of a new product on this topic will replenish the methodological collection of physics teachers and intensify work on the implementation of the Federal State Educational Standard in teaching physics.

All the experiments presented in the work were carried out at physics lessons in grades 7-9 of the Moscow Autonomous Educational Institution Secondary School No. 12, in the process of preparing for the Unified State Exam in physics in grade 11, during the Physics Week, some of them were demonstrated by me at the GMO meeting physics teachers published on the website social network workers education site.

Chapter I. Place of experiment in the study of physics

1. Types of physical experiments

The explanatory note to the programs in physics refers to the need to familiarize students with the methods of science.

Methods of physical science are divided into theoretical and experimental. In this paper, the "experiment" is considered as one of the fundamental methods in the study of physics.

The word "experiment" (from the Latin experimentum) means "test", "experience". The experimental method arose in the natural sciences of modern times (G. Galileo, W. Hilbert). His philosophical understanding was first given in the works of F. Bacon.A learning experiment is a means of learning in the form of experiments specially organized and conducted by a teacher and a student.

Objectives of the educational experiment:

• Solving the main educational tasks;
• Formation and development of cognitive and mental activity;
• Polytechnic training;
• Formation of the scientific outlook of students.

Educational physical experiments can be combined into the following groups:

Demo Experiment, being a means of visualization, contributes to the organization of perception by students educational material, its understanding and memorization; allows for polytechnic education of students; promotes an increase in interest in the study of physics and the creation of motivation for learning. When demonstrating an experiment, it is important that the students themselves can explain the phenomenon they have seen and come to a common conclusion by brainstorming. I often use this method when explaining new material. I also use video fragments with experiments without sound accompaniment on the topic under study and ask them to explain the observed phenomenon. Then I propose to listen to the soundtrack and find an error in my reasoning.
While doinglaboratory workstudents gain experience on their own experimental activities, they havesuch important personal qualities as accuracy in the work of instruments are developed; observance of cleanliness and order in the workplace, in the records that are made during the experiment, organization, perseverance in obtaining results. They form a certain culture of mental and physical labor.

Home experimental tasks and laboratory works are performed by students at home without direct control from the teacher over the progress of work.
Experimental works of this type form in students:
- the ability to observe physical phenomena in nature and in everyday life;
- the ability to perform measurements using measuring instruments used in everyday life;
- interest in experiment and in the study of physics;
- independence and activity.
In order for the student to conduct laboratory work at home, the teacher must conduct a detailed briefing and give a clear algorithm of actions to the student.

Experimental tasksare tasks in which students receive data from experimental conditions. According to a special algorithm, students assemble an experimental setup, perform measurements, and use the measurement results to solve the problem.
Creation of operating models of devices, machines and mechanisms. Every year at school, as part of the week of physics, I hold an inventor competition, to which students submit all their inventive ideas. Before the lesson, they demonstrate their invention and explain what physical phenomena and laws underlie this invention. Students very often involve their parents in working on their inventions, and this becomes a kind of family project. This type of work has a great educational effect.

2.1 Algorithm for creating experimental tasks

The main purpose of experimental tasks is to promote the formation of basic concepts, laws, theories in students, the development of thinking, independence, practical skills, including the ability to observe physical phenomena, perform simple experiments, measurements, handle instruments and materials, analyze the results of an experiment, make generalizations and conclusions.

Students are offered the following algorithm for conducting the experiment:

1. Formulation and justification of the hypothesis that can be used as the basis for the experiment.
2. Determining the purpose of the experiment.
3. Finding out the conditions necessary to achieve the goal of the experiment.
4. Experiment planning.
5. Selection of necessary equipment and materials.
6. Installation collection.
7. Conducting an experiment, accompanied by observations, measurements and recording their results.
8. Mathematical processing of measurement results.
9. Analysis of the results of the experiment, formulation of conclusions.

General structure physical experiment can be represented as:

When conducting any experiment, it is necessary to remember the requirements for the experiment.

Experiment Requirements:

• visibility;
• short duration;
• Persuasiveness, accessibility, reliability;
• Security.

2.2 Results of testing experimental problems

in grades 7-9

Experimental tasks are tasks that are small in volume, directly related to the material being studied, aimed at mastering practical skills that are included in different stages of the lesson (knowledge testing, learning new educational material, consolidated knowledge, independent work in the classroom). After completing the experimental task, it is very important to analyze the results obtained and draw conclusions.

Consider various forms creative tasks that I used in my work at each individual stage of teaching physics in high school:

In 7th grade acquaintance with physical terms, with physical quantities and methods of studying physical phenomena begins. One of the visual methods for studying physics is experiments that can be done both in the classroom and at home. Here, experimental tasks and creative tasks can be effective, where you need to figure out how to measure a physical quantity or how to demonstrate a physical phenomenon. I always appreciate this kind of work.

In 8th grade I use the following forms of experimental tasks:

1) research tasks - as elements of the lesson;

2) experimental homework;

3) make a small report - research on some topics.

In 9th grade the level of complexity of experimental tasks should be higher. Here I am applying:

1) creative tasks for setting up an experiment at the beginning of the lesson - as an element of a problem task; 2) experimental tasks - as a consolidation of the material covered, or as an element of predicting the result; 3) research tasks - as a short-term laboratory work (10-15 minutes).

The use of experimental tasks in the classroom and outside of school hours as homework led to an increase in the cognitive activity of students, increased interest in the study of physics.

I conducted a survey in the 8th grade, in which physics is studied in the second year, and received the following results:

Questions	Answer options	8A class	8B class
Assess your attitude towards the subject.	a) don't like the subject
	b) I'm interested
	c) I love the subject, I want to learn more.
2. How often do you study the subject?	a) regularly
	b) sometimes
	c) very rarely
3. Do you read additional literature on the subject?	a) constantly
	b) sometimes
	c) little, I don’t read at all
4. Do you want to know, understand, get to the bottom of the matter?	a) almost always
	b) sometimes
	c) very rarely
5. Would you like to do experiments outside of school hours?	a) yes, very
	b) sometimes
	c) enough lesson

Of the two 8th grades, there were 24 students who wanted to study physics more deeply and engage in experimental work.

Monitoring the quality of student learning

(teacher Petrosyan O.R.)

Participation in Physics Olympiads and competitions for 4 years

Conclusion

The childhood of a child is not a period of preparation for a future life, but full life. Consequently, education should be based not on the knowledge that will be useful to him someday in the future, but on what the child urgently needs today, on the problems of his real life» (John Dewey).

Each modern school Russia has the necessary minimum equipment for conducting physical experiments presented in the paper. In addition, home experiments are carried out exclusively from improvised means. The creation of the simplest models and mechanisms does not require large expenses, and students take up the work with great interest, involving their parents. This product designed for use by teachers of physics in secondary schools.

Experimental tasks provide students with the opportunity to independently identify the root cause of a physical phenomenon through experience in the process of its direct consideration. Using the simplest equipment, even household items, when conducting an experiment, physics in the minds of students from an abstract system of knowledge turns into a science that studies "the world around us." This highlights the practical importance physical knowledge in ordinary life. In the lessons with the experiment, there is no flow of information coming only from the teacher, there are no bored, indifferent views of students. Systematic and purposeful work on the formation of the skills and abilities of experimental work makes it possible, already at the initial stage of studying physics, to involve students in scientific research, teach them to express their thoughts, conduct a public discussion, and defend their own conclusions. This means making learning more effective and meeting modern requirements.

Literature

1. Bimanova G.M. "Usage innovative technologies when teaching physics in high school". Teacher of secondary school No. 173, Kyzylorda-2013. http://kopilkaurokov.ru/
2. Braverman E.M. Independent conduct of experiments by students // Physics at school, 2000, No. 3 - from 43 - 46.
3. Burov V. A. et al. Frontal experimental tasks in physics in grades 6-7 of secondary school: A guide for teachers / V.A. Burov, S.F. Kabanov, V.I. Sviridov. - M.: Enlightenment, 1981. - 112 p., ill.
4. Gorovaya S.V. "Organization of observations and setting up an experiment in a physics lesson is one of the ways to form key competencies." Physics teacher MOU secondary school No. 27, Komsomolsk-on-Amur-2015

Appendix

Methodological development of physics lessons in grades 7-9 with experimental tasks.

1. Lesson in the 7th grade on the topic “Pressure solids, liquids and gases".

2. Lesson in the 7th grade on the topic "Solving problems to determine the efficiency of the mechanism."

3. Lesson in the 8th grade on the topic “Thermal phenomena. Melting and solidification".

4. Lesson in the 8th grade on the topic "Electrical Phenomena".

5. Lesson in the 9th grade on the topic "Newton's Laws".

A learning experiment is a means of learning in the form of experiments specially organized and conducted by a teacher and a student. Objectives of the educational experiment: Solving the main educational tasks; Formation and development of cognitive and mental activity; Polytechnic training; Formation of the scientific outlook of students. "The joy of seeing and understanding is the most beautiful gift of nature." Albert Einstein

Experimental tasks Creation of operating models, devices, machines and mechanisms Home experimental tasks Laboratory work Demonstration experiment Physical experiment Educational physical experiments can be grouped into the following groups:

The demonstration experiment, being a means of visualization, contributes to the organization of students' perception of educational material, its understanding and memorization; allows for polytechnic education of students; promotes an increase in interest in the study of physics and the creation of motivation for learning. When demonstrating an experiment, it is important that the students themselves can explain the phenomenon they have seen and come to a common conclusion by brainstorming. I often use this method when explaining new material. I also use video fragments with experiments without sound accompaniment on the topic under study and ask them to explain the observed phenomenon. Then I propose to listen to the soundtrack and find an error in my reasoning.

When performing laboratory work, students gain experience in independent experimental activities, they develop such important personal qualities as accuracy in working with devices; observance of cleanliness and order in the workplace, in the records that are made during the experiment, organization, perseverance in obtaining results. They form a certain culture of mental and physical labor.

Home experimental tasks and laboratory work are carried out by students at home without direct control from the teacher over the progress of work. Experimental works of this type form in students: - the ability to observe physical phenomena in nature and in everyday life; - the ability to perform measurements using measuring instruments used in everyday life; - interest in experiment and in the study of physics; - independence and activity. In order for the student to conduct laboratory work at home, the teacher must conduct a detailed briefing and give a clear algorithm of actions to the student.

Experimental tasks are tasks in which students obtain data from experimental conditions. According to a special algorithm, students assemble an experimental setup, perform measurements, and use the measurement results to solve the problem.

Creation of operating models of devices, machines and mechanisms. Every year at school, as part of the week of physics, I hold an inventor competition, to which students submit all their inventive ideas. Before the lesson, they demonstrate their work and explain what physical phenomena and laws underlie this invention. Students very often involve their parents in the work, and this becomes a kind of family project. This type of work has a great educational effect.

Observation Measurement and recording of results Theoretical analysis and mathematical processing of measurement results Conclusions Structure of a physical experiment

When conducting any experiment, it is necessary to remember the requirements for the experiment. Requirements for the experiment: Visualization; short duration; Persuasiveness, accessibility, reliability; Security.

The use of experimental tasks in the classroom and outside of school hours as homework led to an increase in the cognitive activity of students, increased interest in the study of physics. Questions Answer options Grade 8A Grade 8B Assess your attitude to the subject. a) I don't like the subject, 5% 4% b) I'm interested, 85% 68% c) I like the subject, I want to know more. 10% 28% 2. How often do you study the subject? a) regularly 5% 24% b) sometimes 90% 76% c) very rarely 5% 0% 3. Do you read additional literature on the subject? a) constantly 10% 8% b) sometimes 60% 63% c) little, I don't read at all 30% 29% 4. Do you want to know, understand, get to the bottom of the matter? a) almost always 40% 48% b) sometimes 55% 33% c) very rarely 5% 19% 5. Would you like to do experiments outside of school hours? a) yes, very much 60% 57% b) sometimes 20% 29% c) enough lesson 20% 14%

Monitoring the quality of student learning (teacher Petrosyan O.R.)

Participation in Olympiads and competitions in physics for 4 years

“The childhood of a child is not a period of preparation for a future life, but a full life. Consequently, education should be based not on the knowledge that will be useful to him someday in the future, but on what the child urgently needs today, on the problems of his real life ”(John Dewey). Systematic and purposeful work on the formation of the skills and abilities of experimental work makes it possible, already at the initial stage of studying physics, to involve students in scientific research, teach them to express their thoughts, conduct a public discussion, and defend their own conclusions. This means making learning more effective and meeting modern requirements.

"Be pioneers yourself, explorers! If you don't have a spark, you'll never light it in others!" Sukhomlinsky V.A. Thanks for attention!

The effectiveness of using experimental tasks in the classroom is largely determined by their manufacturability, unpretentiousness in equipment, and the breadth of the phenomena under consideration. Based on the simplest equipment and even on household items, the experimental task brings physics closer to us, turning it in the minds of students from an abstract system of knowledge into science, studying the “world around us”.

Mechanics

Task 1. Friction coefficient

The task. Measure the coefficient of sliding friction of a wooden block on the surface of the board (ruler).

Equipment: bar, board, tripod with foot, ruler 30 (40) long cm.

Possible way solutions. We put the bar on the plank, in accordance with Figure 4. Gradually raising one end of the board, we get an inclined plane and achieve uniform sliding of the bar. Since the static friction force is much more power sliding friction, it is necessary to push the bead a little at the beginning of the slide. Use a tripod to fix the desired tilt. We measure the height but and the length of the base of the inclined plane b.

Measurements and error analysis:

The experiment is repeated several times. In this case, this must be done mainly because it is difficult to achieve precisely uniform sliding of the bar along the plane. The results are entered in table 2.

table 2

Measurement errors

a, see	Yes, see	(Yes) 2 ,cm 2	in, cm	Db, cm	(Db) 2 ,cm 2
<a>=12,2		Y( a) 2 = 1,81			Y( b) 2 = 0,32

In addition to random errors, the general error, of course, also includes the usual errors of departure: Yes = Db = 0.5 cm.This amounts to:

Thus, we get:

a = 12.2 ± 1.1 cm, d = 8.6%

b = 27.4 ± 0.7 cm, d = 2.6%

According to the results of the first experience:

The final result of the measurement of the coefficient of friction:

m = 0.46 ± 0.05 d = 10.9%

Task 2. Measuring the height of a house

The task. Imagine that you were asked to use an empty tin can and a stopwatch to measure the height of a house. Would you be able to complete the task? Tell us how to proceed.

Prompt. If the jar is thrown from the roof of the house, then the sound of the jar hitting the earth's surface will be clearly audible.

Solution. Standing on the roof of the house, you need to release the jar from your hands, while simultaneously pressing the start button of the stopwatch. When you hear the sound of the jar hitting the ground, you should stop the stopwatch. Stopwatch indications t are made up of the time of the fall of the bank t 1 and time t 2 , during which the sound of its impact on the earth's surface will reach the observer.

The first time is related to the height of the house h in the following way:

while the relationship between h and t 2 looks like

where from- the speed of sound, which in the calculations we set equal to 340 m/s.

Defining t 1 and t 2 of these expressions and substituting their values ​​into a formula relating t 1 , t 2 and t, we get the irrational equation

From which you can find the height of the house.

In an approximate calculation (especially if the house is not high), the second term on the left can be considered small and discarded. Then

Molecular physics

Task 3. Pencil

The task. Estimate the mechanical work that must be done in order to evenly raise the pencil floating in the vessel to the level of its lower end touching the surface of the water. Consider the position of the pencil vertical. Density of water from 0 = 1000 kg/m 3 .

Equipment: round pencil, almost full water bottle, ruler.

Possible solution. We lower the pencil into the bottle - it will float like a float, in accordance with Figure 5. Let L- the length of the entire pencil, V- its volume, h is the length of the submerged part of the pencil, V 1 - its volume, S- sectional area and d is the diameter of the pencil. Let's find average density pencil from from the condition of body swimming:

from 0 gSh= cgSL, where from= from 0 hL.

Suppose we are pulling a pencil out of the water at a constant speed using a dynamometer. When the pencil floats freely, the dynamometer reads zero. If the pencil is completely pulled out of the water, then the dynamometer will show a force equal to the weight R pencil:

F = P = mg = cgV = c0hLgSL = c0hgрd24

It turns out that the readings of the dynamometer when pulling a pencil out of the water change from 0 to P on linear law, in accordance with Figure 6. At the same time mechanical work BUT will be equal to the area of ​​the selected triangle:

A= 12Ph= from 0 h 2grd 2 8.

For example, when h= 13,4 cm And d = 7,5 mm work is about 0.004 J.

Problem 4. Alloy

The task. Determine the percentage (by weight) of tin in the tin-lead solder. Assume that the volumes of lead and tin in the alloy are conserved. Lead Density from c = 11350 kg/m 3 , tin from 0 = 7300 kg/m 3 .

Equipment: ruler, weight (nut), cylindrical piece of solder, caliper or micrometer. Possible solution. This task is similar to the task of Archimedes to determine the proportion of gold in the royal crown. However, for experiments, tin-lead solder is easier to get than a crown.

By measuring the diameter of a piece of solder D and its length L, find the volume of a cylindrical piece of solder:

V =pD 2 L 4

We determine the mass of solder by making a balance scale. To do this, balance the ruler on the edge of the table (on a pencil, on a ballpoint pen, etc.). Then, using a nut of known mass, we balance a piece of solder on the ruler and, using the equality of the moments of forces, we find the mass of the solder m. Let's write the obvious equalities for the masses, volumes and densities of lead and tin:

m = m c +m o = ccV c +c o V o , V = V c +V o .

Solving these equations together, we find the volume of tin, its mass and its share in the total mass:

V o = rh o cV?mrh o c?rh oo , mo = with o V o , m o m = rh oo V o m

Problem 5. Surface tension

The task. Determine the coefficient of surface tension of water.

Equipment: a plate, water, a spoon, a ruler, a piece of even aluminum wire 15-20 long cm and density 2700 kg/m 3 , micrometer, alcohol, cotton wool.

Possible solution. Pour an almost full plate of water. We put a wire on the edge of the plate so that one end of it touches the water, and the other is outside the plate. The wire performs two functions: it is a balance and is analogous to a wire frame, which is usually pulled out of the water to measure surface tension. Depending on the water level, different positions of the wire can be observed. The most convenient for calculations and measurements is the horizontal arrangement of the wire at a water level of 1-1.5 mm below the rim of the plate, as shown in Figure 7. With a spoon, you can adjust the level by adding or draining water. The wire should be pulled out of the plate until the film of water under the wire begins to break. In this extreme position, the film has a height of 1.5-2 mm, and we can say that the surface tension forces applied to the wire are directed almost vertically downwards.

Let be m- mass of wire, L=L 1 + L 2 - wire length, m/L- mass per unit length of the wire. Let us write down the equilibrium condition for the wire relative to the edge of the plate, i.e. equality of the moments of forces:

F p (L 1 ?x 2)+m 1 gL 12 = m 2 gL 22 .

Substitute here the surface tension force F p =2x at, mass

m 1 =L 1 ml, m 2 = L 2 ml, m= cV= cd 2 L 4

and express the coefficient of surface tension at. Measurements and calculations will be simplified if the water wets the entire length L 1 . Finally we get

at= cd 2 g 8((LL 1 ?1) 2 ?1).

Quantities L And L 1 are measured with a ruler, and the wire diameter d- micrometer.

For example, when L = 15 cm, L 1 = 5,4 cm, d = 1,77 mm we get O = 0,0703 N/m, which is close to the tabular value of 0.0728 N/m.

Task 6. Humidity

The task. Determine the relative humidity in the room.

Equipment: a glass room thermometer, a household refrigerator, a table of pressures of saturated water vapor at various temperatures.

Possible solution. In the conventional method of measuring humidity, the object is cooled below the dew point and it "fogs". Let's do the opposite. The temperature in the refrigerator (about +5 ° C) is well below the room air dew point. Therefore, if you take a chilled glass thermometer out of the refrigerator, it will immediately "fog" - the glass case will become opaque from moisture. Then the thermometer will begin to heat up, and at some point the condensed moisture on it will evaporate - the glass will become transparent. This is the dew point temperature, from which, using the table, you can calculate the relative humidity.

Task 7. Evaporation

The task. Pour an almost full glass of water and put it in a room in a warm place - so that the water evaporates faster. Measure the initial water level with a ruler and record the start time of the experiment. After a few days, the water level will drop due to evaporation. Measure the new water level and record the end time of the experiment. Determine the mass of evaporated water. On average, how many molecules are ejected from the surface of the water in 1 second? Approximately how many molecules are on the surface of water in a glass? Compare these two numbers. Take the diameter of a water molecule equal to d 0 = 0,3 nm. Knowing the specific heat of vaporization, determine the rate of heat transfer ( j/s) water from environment.

Possible solution. Let be d- internal diameter of the glass, from- density of water, M is the molar mass of water, r- specific heat of vaporization, D h- decrease in water level over time t. Then the mass of evaporated water is

m= cv= from D hS= from D hrd 2 4.

This mass contains N=mN A /M molecules, where N A is the Avogadro constant. The number of molecules evaporated in 1 second is

N 1 = Nt= mN A Mt.

If S= pd 2/4 is the surface area of ​​water in a glass, and S 0 = pd 2 0 /4 - the cross-sectional area of ​​​​one molecule, then on the surface of the water in the glass is approximately

N 2 = SS 0 = (dd 0) 2 .

Water for evaporation receives the amount of heat per unit time

Qt= rmt.

If you make any calculations related to molecules, you always get interesting results. For example, let the time t= 5 days in a glass with a diameter d = 65 mm The water level has dropped by h = 1 cm. Then we get that 33 turned into steam G water, for 1 from evaporated N 1 \u003d 2.56 × 10 18 molecules, there were N 2 \u003d 4.69 × 1016 molecules, and 0.19 came from the environment Tue heat. The relationship is interesting N 1 /N 2? 54, from which it can be seen that for 1 from as many molecules evaporated as could be placed in a glass in 54 layers of water.

Task 8. Dissolution

The task. By pouring salt or sugar into boiling water, you will notice that the boiling stops for a short time due to a decrease in the temperature of the water. Determine the amount of heat required to dissolve 1 kg baking soda in room temperature water.

Equipment: home-made calorimeter, thermometer, water, soda, measuring cylinder (glass), known mass weight (nut mass 10 G), a plastic spoon.

Possible solution. The task includes an additional design task for the manufacture of a simple home-made calorimeter. For the inner vessel of the calorimeter, you should take an ordinary aluminum can with a volume of 0.33 liters. The top lid is removed from the can so that an aluminum glass is obtained (weighing only 12 G) with a rigid upper rim. A slot is made inside the upper rim so that the water completely pours out of the jar. The outer plastic shell is made from plastic bottle volume 1.5 l. The bottle is cut into three parts, the upper part is removed, and the middle and lower parts are inserted into each other with some force and tightly fix the inner aluminum can in vertical position. (If there is no calorimeter, then experiments can be carried out in a disposable plastic cup, the mass and heat transfer of which can be neglected).

Beforehand, two measurements should be taken: 1) determine how much soda is placed in a spoon (for this you need to look in a culinary guide or “scoop out” a package of soda of a known mass with this spoon); 2) determine the amount of water - in a small amount of water, the solution will immediately become saturated and part of the soda will not dissolve, in in large numbers water temperature will change by fractions of a degree, making measurements difficult.

Obviously, the amount of heat required to dissolve a substance is proportional to the mass of this substance: Q~m. To record equality, enter the proportionality factor, for example z, which can be called "specific heat of dissolution". Then

Q= zm.

The dissolution of soda is carried out due to the energy released when the vessel with water is cooled. The value of z is found from the following heat balance equation:

mvcv(t 2 -t 1 )+ma cc (t 2 -t 1 ) = zm.

where m v is the mass of water in the calorimeter, m a is the mass of the inner aluminum cup of the calorimeter, m- mass of dissolved soda, ( t 2 -t 1) - lowering the temperature in the calorimeter. The mass of the inner vessel of the calorimeter can be easily found using the rule of moments of force by balancing the vessel and the weight of a known mass using a ruler and string.

Measurements and calculations show that at m= 6 g and m v = 100 G water cools down by 2-2.5 є C, and the value z turns out to be equal to 144-180 kJ/kg.

Task 9. Pot capacity

The task. How can you find the capacity of a pan using a scale and a set of weights?

Prompt. Weigh the empty pot and then the pot of water.

Solution. Let the mass of the empty pan be m 1 , and after filling with water it is m 2. Then the difference m 2 -m 1 gives the mass of water in the volume of the pan. Dividing this difference by the density of water from, find the volume of the pan:

Task 10. How to divide the contents of a glass

The task. There is a cylindrical glass filled to the brim with liquid. How to divide the contents of the glass into two completely equal parts, having one more vessel, but of a different shape and somewhat smaller size?

Prompt. Think about how you can draw a plane that divides the cylinder into two parts of equal volume.

Solution. If through points M And N mentally draw a plane as shown in Figure 1 but, then it will cut the cylinder into two symmetrical and therefore equal in volume figures, in accordance with Figure 8. This implies the solution of the problem.

Gradually tilting the glass, you need to pour out the liquid contained in it until the bottom slightly appears (Figure 1 b). At this point, exactly half of the liquid will remain in the glass.

Electricity

Task 11. Electric "black box"

The "black box" is an opaque closed box that cannot be opened to examine its internal structure. Inside the box are several electrical elements connected to each other in a simple electrical circuit. Usually such elements are: current sources, fixed and variable resistors, capacitors, inductors, semiconductor diodes. Outside the box are several leads.

The main goal of the “black box” task is to “decipher” the “black box” by making the minimum number of electrical measurements using external leads, i.e.:

• - establish which electrical devices are inside the "black box".
• - to establish the scheme of their connection.
• - determine the ratings (resistance values ​​of resistors, capacitor capacitances, etc.)

The task. Three resistors are interconnected and placed in a "black box" with three leads, in accordance with Figure 9. Exactly the same resistors are connected to each other in a different way and placed in a second "black box" with three leads. Determine the resistance of each resistor. Jumpers are not allowed.

Equipment: multimeter.

Measuring the resistance between the leads gave the results:

Drawer #1: R 1-2 = 12Ohm, R 2-3 = 25Ohm, R 1-3 = 37Ohm

Drawer #2: R 1-2 = 5,45Ohm, R 2-3 = 15Ohm, R 1-3 = 20,45Ohm

Possible solution. There are four ways to connect three resistors with three outer leads so that three measurements give different meaning resistance:

1) sequential, 2) mixed, 3) star, 4) delta, in accordance with Figure 10.

Let's show the sequence of search for answers.

A characteristic feature of the first two schemes is that one of the measurements is equal to the sum of the other two, which corresponds to the condition of the problem:

Therefore, in one box there is a serial connection, but then in the other - mixed, since the measurements do not match, although the resistor values ​​are the same.

It is known that the relation always holds

And since R 1-3 left more than R 1-3 on the right, then in the left box (No. 1) there is a serial connection, and in the right (No. 2) - mixed.

The serial connection in the left box includes resistors with ratings of 12 or 25 Ohm. Since neither one nor the other value is observed as part of a mixed connection, therefore, the value of one of the resistors R 1 = 15Ohm.

Other denominations: R 2 = 12Ohm And R 3 = 10Ohm.

Obviously, the same results can be reached with the help of a different chain of reasoning.

We also note that there are 5 more combinations of schemes, each with two "black boxes" out of the four given. The most cumbersome mathematical part of the problem is to "decode" the black box, which is known to contain a triangle.

In conclusion, we note that not everything can go as smoothly as in this example. The values ​​of resistances or other electrical quantities, of course, contain errors. And, for example, the ratio can be fulfilled only approximately.

Task 12. Air temperature in the room

The task. It's snowing outside, but the room is warm. Unfortunately, there is nothing to measure the temperature - there is no thermometer. But on the other hand, there is a battery, a very accurate voltmeter and the same ammeter, as much copper wire as you like, and a detailed physical reference book. Is it possible to use them to find the air temperature in the room?

Prompt. When a metal is heated, its resistance increases linearly.

Solution. We connect the battery in series, turn on the coil of wire and turn on the ammeter so that it shows the voltage on the coil, in accordance with Figure 11. Let's record the readings of the instruments and calculate the resistance of the coil at room temperature:

After that, we will bring snow from the street, immerse a skein in it and, after waiting a bit for the snow to begin to melt, and the wire to its temperature, in the same way we determine the resistance of the wire R 0 at the temperature of melting snow, i.e. at 0 є FROM. Using then the relationship between the resistance of the conductor and its temperature

find the air temperature in the room:

The calculation uses the value of the temperature coefficient of resistance b taken from the handbook. At room temperature for pure copper b= 0,0043 hail - one . If the content of impurities in the copper from which the wire is made is not particularly high, and electrical measuring instruments have an accuracy class of 0.1, then the air temperature can be determined with an error much less than one degree.

Optics

Task 13.

The task. It is required to find the radius of a spherical mirror (or the radius of curvature concave lens) with a stopwatch and a steel ball of known radius. How to do it?

Prompt. The center of a ball rolling on the surface of a mirror makes the same movement as a pendulum.

Solution. You should place the mirror horizontally and lower the ball on it. If the ball is not lowered to the lowest point, it will begin to move along the surface of the mirror. It is easy to guess that if the ball moves without rotation (i.e., slides on the surface of the mirror), then its movement is completely similar to the movement of a pendulum with a suspension length R - r. Then from the pendulum formula

we can find the quantity we are interested in:

Period T determined using a stopwatch, and r known by convention.

Since the friction is usually strong enough for the ball to move on the surface of the mirror with rotation, this solution does not agree well with experiment. Actually

Let's give an example of a research problem for the whole lesson.

Task 14. Oscillation features of a torsion pendulum.

The task. Explore the features of the oscillation of a torsion pendulum and describe the main patterns of its movement.

Equipment: a tripod with a clutch and foot, pieces of copper, steel and nichrome wire approx. 1m and various diameters, for example 0.3, 0.50, 0.65, 1.0 mm, thin light wooden stick 15-20 long cm, plasticine, paper clip, ruler, protractor, stopwatch.

The general view of the torsion pendulum should be in accordance with Figure 12. A clip, bent in a certain way, serves to balance the rod with the weights. The pendulum, taken out of the state of equilibrium, begins to perform rotational-oscillatory motion.

In advance, you need to make pairs of balls of different masses from plasticine. The masses of the balls are proportional to the cube of their diameters, so it is possible to build a series, for example: m 1 = 1, m 2 = 2,5, m 3 = 5,2, m 3 = 6,8, m 4 = 8,3 rel. units

The diameter of the wires can be given to students in advance, or they can be given the opportunity to take these measurements themselves using a caliper or micrometer.

Note. The success of the study largely depends on the correct selection of equipment, especially the diameters of the issued wires. In addition, it is desirable that the suspension of the torsion pendulum be in a taut state during the experiments, for which the masses of the weights must be sufficiently large.

The theme of the study of a torsion pendulum follows from the assumption of the harmonic nature of its oscillations. The general list of experimental observations that can be carried out on this problem and on the proposed equipment is quite large. Here are the most simple and affordable.

• - Does the period of oscillations depend on the amplitude (angle of rotation)?
• - Does the period of oscillation depend on the length of the pendulum suspension?
• - Does the period of oscillation of the pendulum depend on the mass of the weights?
• - Does the period of oscillation of the pendulum depend on the position of the weights on the rod?
• - Does the oscillation period depend on the wire diameter?

Naturally, it is required not only to answer the questions in monosyllables, but also to investigate the nature of the expected dependencies.

Using the technique of analogies, we put forward hypotheses about the oscillations of a torsion pendulum, comparing it with a mathematical pendulum studied in the school curriculum. We take as a basis the oscillation period and its dependence on various parameters of the pendulum. We propose the following hypotheses. Oscillation period of a torsion pendulum:

At small angles of rotation does not depend on the amplitude;

• - proportional to the square root of the length of the suspension - T;
• - proportional to the square root of the mass of the load - T;
• - proportional to distance from the center of suspension to the centers of loads - Tr;
• - inversely proportional to the square of the wire diameter - T1/d 2 .

In addition, the oscillation period depends on the suspension material: copper, steel, nichrome. There are also a number of hypotheses here, we suggest checking them yourself.

1. We study the dependence of the period of oscillation of the pendulum on the amplitude (angle of rotation). The measurement results are presented in table 3:

Table 3

The dependence of the period of oscillation of the pendulum on the amplitude

L= 60cm, m = 8,3r, r = 12cm, d= 0,5mm

Output. In the range up to 180, the dependence of the oscillation period of the torsion pendulum on the amplitude is not detected. The scatter of measurement results can be explained by errors in measuring the oscillation period and random causes.

To "open" other dependencies, you need to change only one parameter, leaving all others unchanged. Mathematical processing of results is best done graphically.

2. We study the dependence of the period of oscillation of the pendulum on its length: Т = f(l). At the same time, we do not change m, r, d. The measurement results are presented in table 4:

Table 4

The dependence of the period of oscillation of the pendulum on the length

m = 8,3rel. units, r = 12cm, d= 0,5mm

dependency graph T from l is a curved ascending line similar to a dependency, according to Figure 13 but T 2 =l, in accordance with Figure 13, b.

Output. The period of oscillation of a torsion pendulum is directly proportional to the square root of the length of the suspension. Some scatter of points can be explained by errors in measurements of the period of oscillations and the length of the pendulum

3. We study the dependence of the period of oscillation of the pendulum on the mass of goods: Т=f(m). At the same time, we do not change l, r, d. The measurement results are presented in table 5:

Table 5

The dependence of the period of oscillation of the pendulum on the mass of loads

l = 0,6m, r= 12cm, d= 0,5mm

dependency graph T from m is a curved ascending line similar to a dependency, as shown in Figure 14 but. To verify this, we build a dependency T 2 =f(m), according to figure 14 b.

Output. The period of oscillation of a torsion pendulum is directly proportional to the square root of the mass of the weights. Some scatter of points can be explained by errors in measurements of the period of oscillations and masses of goods, as well as random causes.

4. We study the dependence of the period of oscillation of the pendulum on the position of the weights: Т = f(r). At the same time, we do not change l, m, d. The measurement results are presented in table 6:

Table 6

The dependence of the period of oscillation of the pendulum on the position of the weights

m = 8,3rel.un., l = 0,6m, d = 0,5mm

Output. The period of oscillation of a torsion pendulum is directly proportional to the distance r. Some scatter of points can be explained by measurement errors of the oscillation period and distance r as well as random causes.

We study the dependence of the period of oscillation of the pendulum on the diameter of the wire: T = f(d), in accordance with figure 15 . However, we do not change m, r, l.

The measurement results are presented in table 7.

Table 7

The dependence of the oscillation period of the pendulum on the diameter of the wire

m = 8.3 relative units, r = 12 cm, l = 0.6 m

dependency graph T from d represents a falling curve, in accordance with Figure 16 but. It can be assumed that this is a dependence, where n= 1, 2, 3, etc. To test these assumptions, it is necessary to build graphs, etc. Of all such graphs, the graph is the most linear, in accordance with Figure 16 b.

Output. The period of oscillation of a torsion pendulum is inversely proportional to the square of the suspension wire diameter. Some scatter of points can be explained by measurement errors of the oscillation period and wire diameter d as well as random causes.

The conducted studies allow us to conclude that the oscillation period of a torsion pendulum should be calculated by the formula, where k- coefficient of proportionality, which also depends on the elastic properties of the suspension material - torsion modulus, shear modulus.

1. Explanatory note.

Teaching physics in high school is based on the basic school physics course subject to differentiation. The content of education should contribute to the implementation of a multi-level approach. Lyceum No. 44 is aimed at the optimal development of the creative abilities of students with a special interest in the field of physics; this level of teaching is carried out in classes with in-depth study of physics.

The objects of study in a physics course at an accessible level for students, along with fundamental physical concepts and laws, should be an experiment as a method of cognition, a method of building models and a method of their theoretical analysis. Lyceum graduates should understand the essence of models of natural objects (processes) and hypotheses, how theoretical conclusions are made, how to experimentally test models, hypotheses and theoretical conclusions.

In the Lyceum, the number of hours in physics in advanced classes does not correspond to the new status of the Physics and Mathematics Lyceum: in 9 classes - 2 hours. In this regard, it is proposed to replace the technology lessons in the 9th grade (1 hour per week with division into two groups) with practical experimental physics in addition to the main lessons on the clock grid.

The purpose of the course is to provide students with the opportunity to satisfy their individual interest in the study of practical applications of physics in the process of cognitive and creative activity during independent experiments and research.

The main objective of the course is to help students make an informed choice of a profile for further education.

The program consists of the following parts: a) errors; b) laboratory work; c) experimental work; d) experimental tasks; e) testing.

In elective classes, students will get acquainted in practice with those types of activities that are leading in many engineering and technical professions related to the practical application of physics. The experience of independently performing, first, simple physical experiments, then tasks of a research and design type will either make sure that the preliminary choice is correct, or change your choice and try yourself in some other direction.

At the same time, theoretical studies are expedient only at the first stage when forming a group and determining the interests and abilities of students.

The main forms of classes should be the practical work of students in a physical laboratory and the performance of simple experimental tasks at home.

In practical classes, when performing laboratory work, students will be able to acquire the skills of planning a physical experiment in accordance with the task, learn to choose a rational method of measurement, perform an experiment and process its results. The implementation of practical and experimental tasks will allow you to apply the acquired skills in a non-standard environment, to become competent in many practical issues.

All types of practical tasks are designed for the use of typical equipment of a physics classroom and can be performed in the form of laboratory work or as experimental tasks of your choice.

The elective course is aimed at educating schoolchildren in their abilities and the ability to use a variety of appliances and household appliances in Everyday life, as well as the development of interest in a close examination of familiar phenomena and objects. The desire to understand, to understand the essence of phenomena, the structure of things that serve a person all his life, will inevitably require additional knowledge, push him to self-education, make him observe, think, read, invent.

Measurement methods physical quantities(2 hours).

Basic and derived physical quantities and their measurements. Units and standards of values. Absolute and relative errors of direct measurements. Measuring devices, tools, measures. Instrumental errors and reading errors. Instrument accuracy classes. The boundaries of systematic errors and methods for their evaluation. Random measurement errors and estimation of their boundaries.

Stages of planning and execution of the experiment. Experimental precautions. Accounting for the influence of measuring instruments on the process under study. Choice of measurement method and measuring instruments.

Ways to control the results of measurements. Recording measurement results. Tables and graphs. Processing of measurement results. Discussion and presentation of the obtained results.

Laboratory work (16 hours).

1. Calculation of measurement errors of physical quantities.
2. The study of uniformly accelerated motion.
3. Determination of the acceleration of a body in uniformly accelerated motion.
4. Measurement of body weight.
5. Study of Newton's second law.
6. Determining the stiffness of a spring.
7. Determination of the coefficient of sliding friction.
8. Study of the motion of a body thrown horizontally.
9. The study of the motion of a body in a circle under the action of several forces.
10. Elucidation of the conditions for the equilibrium of bodies under the action of several forces.
11. Determining the center of gravity of a flat plate.
12. Study of the law of conservation of momentum.
13. Measuring the efficiency of an inclined plane.
14. Comparison of the work done with the change in body energy.
15. Study of the law of conservation of energy.
16. Measurement of free fall acceleration with a pendulum.

Experimental work (4 hours).

1. Calculation of average and instantaneous speed.
2. Speed ​​measurement at the bottom of an inclined plane.
3. Calculation and measurement of the speed of a ball rolling down an inclined chute.
4. Study of the oscillations of a spring pendulum.

Experimental tasks (10 hours).

1. Solving experimental problems of grade 7 (2 hours).
2. Solving experimental problems of grade 8 (2 hours).
3. Solving experimental problems of grade 9 (2 hours).
4. Solving experimental problems using a computer (4 hours).

Tested task (1 hour).

Generalizing lesson (1 hour).

3. Certification of students.

The test form of assessing students' achievements is most consistent with the features of elective classes. It is advisable to set a credit for the performed laboratory work according to the submitted written report, which briefly describes the conditions of the experiment. The results of measurements are presented in a systematic way and conclusions are drawn.

Based on the results of performing creative experimental tasks, in addition to written reports, it is useful to practice reports in a general group lesson with a demonstration of experiments performed and devices made. To conduct the general results of the classes of the whole group, it is possible to hold a competition of creative works. At this competition, students will be able not only to demonstrate the experimental installation in action, but also to talk about its originality and capabilities. Here it is especially important to draw up your report with graphs, tables, briefly and emotionally talk about the most important thing. In this case, it becomes possible to see and evaluate your work and yourself against the background of other interesting works and equally enthusiastic people.

The student's final credit for the entire elective course can be set, for example, according to the following criteria: completion of at least half of the laboratory work; fulfillment of at least one experimental task of a research or design type; active participation in the preparation and holding of seminars, discussions, competitions.

The proposed criteria for assessing student achievement are intended to serve as a guide only, but are not mandatory. Based on their experience, the teacher may set other criteria.

4. Literature:

1. Demonstration experiment in physics in high school./Ed. A. A. Pokrov
   sky. Part 1. - M .: Education, 1978.
2. Methods of teaching physics in grades 7-11 of secondary school./Edited by V.P.
   Orekhov and A.V. Usova. - M.: Education, 1999.
3. Martynov I.M., Khozyainova E.N. Didactic material in physics. Grade 9 - M.:
   Enlightenment, 1995.
4. V.A. Burov, A.I. Ivanov, V.I. Sviridov. Frontal experimental tasks for
   Physics. Grade 9. - M: Education. 1988.
5. Rymkevich A.P., Rymkevich P.A. Collection of tasks in physics for grades 9-11. – M.: Pro
   illumination, 2000.
6. Stepanova G.N. Collection of tasks in physics: For grades 9-11 of general education
   decisions. - M.: Enlightenment, 1998.
7. Gorodetsky D.N., Penkov I.A. Verification work in physics. – Minsk “Highest
   school”, 1987
8. V.A. Burov, S.F. Kabanov, V.I. Sviridov. “Front experimental tasks on
   physics." - M: Enlightenment. 1988
9. Kikoin I.K., Kikoin A.K. Physics: Textbook for 10 grades - M .: Education, 2003

T THEMATIC PLANNING FOR PHYSICS IN 9th CLASS

Elective course: “Practical and experimental physics”

(in-depth study - 34 hours)

Step - third

Level - advanced

№	Type of lesson	Clock	Lesson content	D / s
1	Lecture	1h	Safety engineering.	Abstract
2	Lecture	1h	Measurement errors of physical quantities.	Abstract
3	Lab #1	1h	Calculation of measurement errors of physical quantities	Finish calculations
4		1h		tasks
5	Experimental work	1h	Calculation of average and instantaneous speed	Finish calculations
6	Lab #2	1h	Study of uniformly accelerated motion	Finish calculations
7	Laboratory work number 3.	1 hour	Determination of the acceleration of a body in uniformly accelerated motion.	Finish calculations
8	Experimental work	1 hour	Speed ​​measurement at the bottom of an inclined plane.	Finish calculations
9	Lab #4	1h	Measurement of body mass	Finish calculations
10	Lab #5	1h	Learning Newton's Second Law	Finish calculations
11	Lab #6	1 hour	Determining the stiffness of a spring.	Finish calculations
12	Lab #7	1 hour	Determination of the coefficient of sliding friction.	Finish calculations
13	Lab #8	1 hour	Study of the motion of a body thrown horizontally.	Finish calculations
14	Lab #9	1 hour	The study of the motion of a body in a circle under the action of several forces.	Finish calculations
15	Solution of experimental problems	1h	Solving experimental problems of grade 7	tasks
16	Lab #10	1 hour	Elucidation of the conditions for the equilibrium of bodies under the action of several forces.	Finish calculations
17	Lab #11	1 hour	Determining the center of gravity of a flat plate.	Finish calculations
18	Solution of experimental problems	1h		tasks
19	Solution of experimental problems	1h	Solving experimental problems of grade 8	tasks
20	Lab #12	1h	Studying the Law of Conservation of Momentum	Finish calculations
21	Lab #13	1h	Measuring the efficiency of an inclined plane	Finish calculations
22	Lab #14	1 hour	Comparison of the work done with the change in body energy”	Finish calculations
23	Lab #15	1h	Studying the Law of Conservation of Energy	Finish calculations
24	Experimental work	1h	Calculation and measurement of the speed of a ball rolling down an inclined chute	Finish calculations
25	Solution of experimental problems	1h		Tasks
26	Solution of experimental problems	1h	Solving experimental problems of grade 9	tasks
27	Experimental work	1h	Studying the oscillations of a spring pendulum	Finish calculations
28	Lab #16	1h	Measuring free fall acceleration with a pendulum	Finish calculations
29		1h	Solving experimental problems of grade 9	Finish calculations
30	Solving experimental problems using a computer	1h	Solving experimental problems using a computer	Finish calculations
31	Solving experimental problems using a computer	1h	Solving experimental problems using a computer	Finish calculations
32	Solving experimental problems using a computer	1h	Solving experimental problems using a computer	Finish calculations
33	Tested task	1h	Test
34	Generalizing lesson	1h	Summing up and tasks for the next year

LITERATURE:

1. Demonstration experiment in physics in high school./Ed. A. A. Pokrovsky. Part 1. - M .: Education, 1978.
2. Methods of teaching physics in grades 7-11 of secondary school./Edited by V.P. Orekhov and A.V. Usova. - M.: Education, 1999.
3. Enohovich A.S. Handbook of Physics. - M.: Enlightenment, 1978.
4. Martynov I.M., Khozyainova E.N. Didactic material in physics. Grade 9 - M.: Enlightenment, 1995.
5. Skrelin L.I. Didactic material in physics. Grade 9 – M.: Enlightenment, 1998.
6. Reader in Physics / Ed. B.I. Spassky. – M.: Enlightenment, 1982.
7. Rymkevich A.P., Rymkevich P.A. Collection of tasks in physics for grades 9-11. – M.: Enlightenment, 2000.
8. Stepanova G.N. Collection of tasks in physics: For grades 9-11 of educational institutions. - M.: Enlightenment, 1998.
9. Gorodetsky D.N., Penkov I.A. Verification work in physics. – Minsk “The Highest School”, 1987.

Attachment 1

Lesson No. 1: “Measurement of physical quantities and estimation of measurement errors”.

Lesson objectives: 1. To introduce students to the mathematical processing of measurement results and teach how to present experimental data;

2. Development of computing abilities, memory and attention.

During the classes

The results of any physical experiment must be able to analyze. This means that in the laboratory it is necessary to learn not only to measure various physical quantities, but also to check and find the relationship between them, to compare the results of the experiment with the conclusions of the theory.

But what does it mean to measure a physical quantity? What if the desired value cannot be measured directly and its value is found from the value of other quantities?

Measurement is understood as a comparison of the measured value with another value, taken as a unit of measurement.

The measurement is divided into direct and indirect.

In direct measurements, the quantity to be determined is compared with the unit of measurement directly or with the help of a measuring instrument calibrated in the appropriate units.

In indirect measurements, the desired value is determined (calculated) from the results of direct measurements of other quantities that are associated with the measured value by a certain functional dependence.

When measuring any physical quantity, you usually have to perform three sequential operations:

1. Selection, testing and installation of devices;
2. Observation of instrument readings and counting;
3. Calculation of the desired value from the measurement results, evaluation of errors.

Errors in measurement results.

The true value of a physical quantity is usually impossible to determine with absolute accuracy. Each measurement gives the value of the determined quantity x with some error? x. This means that the true value lies in the interval

x meas - dx< х ист < х изм + dх, (1)

where x meas - the value of x, obtained during the measurement; ?x characterizes the accuracy of x measurement. The value? x is called the absolute error with which x is determined.

All errors are divided into systematic, random and misses (mistakes). The causes of errors are varied. Understand possible reasons errors and reduce them to a minimum - this means competently setting up an experiment. It is clear that this is not an easy task.

A systematic error is such an error that remains constant or regularly changes during repeated measurements of the same value.

Such errors arise as a result of the design features of measuring instruments, the inaccuracy of the research method, any omissions of the experimenter, as well as when using inaccurate formulas, rounded constants for calculations.

A measuring device is a device that compares the measured value with a unit of measurement.

In any device, one or another systematic error is inherent, which cannot be eliminated, but the order of which can be taken into account.

Systematic errors either increase or decrease the measurement results, that is, these errors are characterized by a constant sign.

Random errors are errors that cannot be prevented.

Therefore, they can have a certain effect on a single measurement, but with multiple measurements they obey statistical laws and their influence on the measurement results can be taken into account or significantly reduced.

Slips and gross errors are excessively large errors that clearly distort the measurement result.

This class of errors is caused most often by incorrect actions of the observer. Measurements containing misses and gross errors should be discarded.

Measurements can be taken in terms of their accuracy technical And laboratory methods.

In this case, they are satisfied with such an accuracy at which the error does not exceed some certain, predetermined value, determined by the error of the measuring equipment used.

At laboratory methods measurements, it is required to indicate the value of the measured quantity more accurately than it allows for its single measurement by the technical method.

Then make several measurements and calculate the arithmetic mean of the obtained values, which is taken as the most reliable value of the measured value. Then, the accuracy of the measurement result is assessed (accounting for random errors).

From the possibility of carrying out measurements by two methods, the existence of two methods for assessing the accuracy of measurements follows: technical and laboratory.

Instrument accuracy classes.

To characterize most measuring instruments, the concept of the reduced error E p (accuracy class) is often used.

The reduced error is the ratio of the absolute error?x to the limit value x pr of the measured value (that is, its highest value that can be measured on the instrument scale).

The reduced error, being essentially a relative error, expressed as a percentage:

E p \u003d / dx / x pr / * 100%

According to the given error, the devices are divided into seven classes: 0.1; 0.2; 0.5; 1.0; 1.5; 2.5; 4.

Instruments of accuracy class 0.1; 0.2; 0.5 is used for accurate laboratory measurements and is called precision.

In technology, devices of classes 1, 0 are used; 1.5; 2.5 and 4 (technical). The accuracy class of the device is indicated on the scale of the device. If there is no such designation on the scale, but this device is out of class, that is, its reduced error is more than 4%. In cases where the accuracy class is not indicated on the instrument, the absolute error is taken equal to half the value of the smallest division.

So, when measuring with a ruler, the smallest division of which is 1 mm, an error of up to 0.5 mm is allowed. For devices equipped with a vernier, the error determined by the vernier is taken as the instrument error (for calipers - 0.1 mm or 0.05 mm; for micrometer - 0.01 mm).

Annex 2

Lab: "Measuring the efficiency of an inclined plane."

Equipment: wooden board, wooden block, tripod, dynamometer, measuring ruler.

Task. Investigate the dependence of the efficiency of an inclined plane and the gain in force obtained with its help from the angle of inclination of the plane to the horizon.

The efficiency of any simple mechanism is equal to the ratio of useful work A floor to the perfect work A owls and is expressed as a percentage:

n \u003d A floor / A cos * 100% (1).

In the absence of friction, the efficiency of a simple mechanism, including an inclined plane, is equal to one. In this case, the perfect work A owl of the force F t applied to the body and directed upward along the inclined plane is equal to the useful work A field.

A sex \u003d A owl.

Denoting the path traveled by the body along the inclined plane with the letter S, the height of the rise? , we get F*S=hgm.

In this case, the gain in strength will be equal to: k \u003d gm / F \u003d l / h.

In real conditions, the action of the friction force reduces the efficiency of the inclined plane and reduces the gain in force.

For definitions of efficiency inclined plane of the gain in force obtained with its help, the expression should be used:

n \u003d hgm / F t l * 100% (2), k \u003d gm / F t (3).

The purpose of the work is to measure the efficiency of an inclined plane and the gain in force at different angles? its inclination to the horizon and explain the result.

The order of the work.

1. Assemble the unit according to fig.1. Measure height? and the length l of the inclined plane (Fig. 2).

2. Calculate the maximum possible gain in force obtained for a given plane slope (a=30).

3. Lay the block on an inclined plane. Attaching a dynamometer to it, evenly pull it up along the inclined plane. Measure the traction force F t.

4. Measure the force of gravity mg of the bar with a dynamometer and find the experimental value of the gain in force obtained with the help of an inclined plane: k = gm / F t.

5. Calculate the efficiency of an inclined plane for a given angle of inclination

n \u003d hgm / F t l * 100%

6. Repeat the measurements at other angles of inclination of the plane: a 2 =45?, a 3 =60?.

7. Enter the results of measurements and calculations in the table:

№	a	m, kg	h, m	l, m	F , N	to	n,%
1	30
2	45
3	60

8. Additional task

Compare the obtained theoretical dependence n(a) and k(a) with the experimental results.

Test questions.

1. What is the purpose of an inclined plane?
2. How can the efficiency of an inclined plane be increased?
3. How can you increase the gain in strength obtained with the help of an inclined plane?
4. Does the efficiency of an inclined plane depend on the mass of the load?
5. Explain qualitatively the dependence of the efficiency of an inclined plane and the gain in force obtained with its help on the angle of inclination of the plane.

Annex 3

List of experimental tasks for grade 7

1. Measuring the dimensions of the bar.
2. Measuring the volume of liquid with a beaker.
3. Liquid density measurement.
4. Measurement of the density of a solid body.

All work is carried out with the calculation of errors and verification

dimensions.

1. Measurement of body weight with a lever.
2. Calculation of the gain in strength of the tools in which it is applied (scissors, wire cutters, pliers)
3. Observation of the dependence of the kinetic energy of a body on its speed and mass.
4. Find out what the friction force depends on experimentally.

List of experimental tasks for grade 8

1. Action observation electric current(thermal, chemical, magnetic and, if possible, physiological).
2. Calculation of the characteristics of a mixed connection of conductors.
3. Definition resistivity conductor with error estimation.
4. Observation of the phenomenon of electromagnetic induction.

1. Observation of the absorption of energy during the melting of ice.
2. Observation of the release of energy during the crystallization of hyposulfite.
3. Observation of energy absorption during the evaporation of liquids.
4. Observation of the dependence of the rate of evaporation of a liquid on the type of liquid, its free surface area, temperature, and the rate of vapor removal.
5. Determination of air humidity in the office.

List of experimental work grade 9

1. 1. Measurement of the modules of the angular and linear velocities of the body with uniform motion in a circle.
2. 2.Measurement of the module of centripetal acceleration of the body with uniform motion in a circle.
3. 3. Observation of the dependence of the modules of the thread tension forces on the angle between them at a constant resultant force.
4. 4. Study of Newton's third law.

1. Observation of the change in the modulus of the weight of a body moving with acceleration.
2. Elucidation of the equilibrium conditions for a body with an axis of rotation under the action of forces on it.
3. Study of the Law of Conservation of Momentum in the Elastic Collision of Bodies.
4. Measurement of the efficiency of the moving block.

Appendix 4

Experimental tasks

Measuring the dimensions of the bar

Instruments and materials (Fig. 2): 1) measuring ruler, 2) wooden block.

Work order:

• Calculate the scale division value of the ruler.
• Specify the limit of this scale.
• Measure the length, width, height of the bar with a ruler.
• Record the results of all measurements in a notebook.

Measuring the volume of liquid with a beaker

Devices and materials (Fig. 3):

• measuring cylinder (beaker),
• a glass of water.

Work order

1. Calculate the scale division of the beaker.
2. Sketch in your notebook a part of the scale of the beaker and make a note explaining the procedure for calculating the price of the division of the scale.
3. Specify the limit of this scale.
4. Measure the volume of water in the glass using a beaker. " "
5. Record the measurement result in a notebook.
6. Pour the water back into the glass.

Pour into a beaker, for example, 20 ml of water. After checking by the teacher, add more water to it, bringing the level to a division, for example, 50 ml. How much water was added to the beaker

Liquid Density Measurement

Instruments and materials (Fig. 14): 1) training scales, 2) weights, 3) measuring cylinder (beaker), 4) a glass of water.

Work order

1. Write down: the price of division of the scale of the beaker; the upper limit of the beaker scale.
2. Measure the mass of a glass of water using a scale.
3. Pour the water from the glass into the beaker and measure the weight of the empty glass.
4. Calculate the mass of water in the beaker.
5. Measure the volume of water in the beaker.
6. Calculate the density of water.

Calculation of body mass by its density and volume

Instruments and materials (Fig. 15): 1) training scales, 2) weights, 3) measuring cylinder (beaker) with water, 4) body irregular shape on a thread, 5) table of densities.

Work order(Fig. 15)

1. Measure the volume of the body with a beaker.
2. Calculate the mass of the body.
3. Check the result of the calculation of body weight with the help of scales.
4. Record the results of measurements and calculations in a notebook.

Calculating the volume of a body from its density and mass

Instruments and materials (Fig. 15): 1) training scales, 2) weights, 3) a measuring cylinder (beaker) with water, 4) an irregularly shaped body on a thread, b) a table of densities.

Work order

1. Write down the substance that makes up an irregularly shaped body.
2. Find the value of the density of this substance in the table.
3. Measure your body weight with a scale.
4. Calculate the volume of the body.
5. Check the result of calculating the volume of the body using a beaker.
6. Record the results of measurements and calculations in a notebook.

Study of the dependence of the force of sliding friction on the type of rubbing surfaces

Instruments and materials (Fig. 23): 1) dynamometer, 2) tribometer 3) weights with two hooks -2 pcs., 4) a sheet of paper, 5) a sheet of sandpaper.

Work order

1. Prepare a table in your notebook to record the measurement results:

2. Calculate the scale division value of the dynamometer.
3. Measure the sliding friction force of the bar with two weights:

4. Record the measurement results in a table.

5. Answer the questions:

1. Does the force of sliding friction depend on:
   a) on the type of rubbing surfaces?
   b) from the roughness of rubbing surfaces?
2. What are the ways to increase and decrease the force of sliding friction? (Fig. 24):
   1) dynamometer, 2) tribometer.

Study of the dependence of the sliding friction force on the pressure force and independence of the area of ​​rubbing surfaces

Devices and materials: 1) dynamometer, 2) tribometer; 3) loads with two hooks - 2 pcs.

Work order

1. Calculate the division value of the dynamometer scale.
2. Put a bar with a large edge on the tribometer ruler, and a load on it and measure the sliding friction force of the bar along the ruler (Fig. 24, a).
3. Put a second load on the bar and again measure the sliding friction force of the bar along the ruler (Fig. 24, b).
4. Put a bar on the ruler with a smaller edge, put two weights on it again and again measure the sliding friction force of the bar along the ruler (Fig. 24, in)
5. 5. Answer the question: does the force of sliding friction depend:
   a) on the force of pressure, and if it depends, then how?
   b) on the area of ​​rubbing surfaces at a constant pressure force?

Measuring body weight with a lever

Devices and materials: 1) lever-ruler, 2) measuring ruler, 3) dynamometer, 4) load with two hooks, 5) metal cylinder, 6) tripod.

Work order

1. Hang the lever on the axis fixed in the tripod sleeve. Rotate the nuts on the ends of the lever until it is in a horizontal position.
2. Hang a metal cylinder from the left side of the lever, and a load from the right side, having previously measured its weight with a dynamometer. Empirically achieve balance of the lever with the load.
3. Measure the shoulders of the forces acting on the lever.
4. Using the lever balance rule, calculate the weight of the metal cylinder.
5. Measure the weight of a metal cylinder with a dynamometer and compare the result with the calculated one.
6. Record the results of measurements and calculations in a notebook.
7. Answer the questions: will the result of the experiment change if:

• balance the lever with a different length of the arms of the forces acting on it?
• hang the cylinder to the right side of the lever, and the balancing weight - to the left?

Calculation of gain in strength of instruments in which leverage is applied

"Instruments and materials (Fig. 45): 1) scissors, 2) wire cutters, 3) pliers, 4) measuring ruler.

Work order

1. Familiarize yourself with the device of the tool offered to you, in which the lever is used: find the axis of rotation, the points of application of forces.
2. Measure the shoulders of the forces.
3. Calculate approximately within what limits the calculation can change
   play in force when using this tool.
4. Record the results of measurements and calculations in a notebook.
5. Answer the questions:

• How should the cut material be positioned in the scissors in order to obtain the greatest gain in strength?
• How should you hold the wire cutters in your hand to get the most gain in strength?

Observation of the dependence of the kinetic energy of a body on its speed and mass

Devices and materials (Fig. 50): I) balls of different masses - 2 pcs., 2) chute, 3) bar, 4) measuring tape, 5) tripod. Rice. fifty.

Work order

1. Support the chute in an inclined position with a tripod, as shown in Figure 50. Attach a block of wood to the bottom end of the chute.
2. Put a ball of smaller mass in the middle of the chute and, releasing it, observe how the ball, rolling down the chute and hitting a wooden block, moves the latter a certain distance, doing work to overcome the friction force.
3. Measure the distance the block has moved.
4. Repeat the experiment by dropping the ball from the upper end of the chute, and again measure the distance that the block has moved.
5. Start a ball of larger mass from the middle of the chute and again measure the movement of the bar.

Measurement of modules of angular and linear velocities of a body with uniform motion in a circle

Devices and materials * 1) a ball with a diameter of 25 mm on a thread 200 mm long, 2) a measuring ruler 30-35 cm with millimeter divisions, 3) a watch with a second hand or a mechanical metronome (one per class).

Work order

1. Lift the ball by the end of the thread above the ruler and bring it into uniform motion around the circle so that during rotation it passes through the zero and, for example, the tenth division of the scale each time (Fig. 9). To obtain a stable movement of the ball, place the elbow of the hand holding the thread on the table
2. Measure the time, for example, 30 full revolutions of the ball.
3. Knowing the time of movement, the number of revolutions and the radius of rotation, calculate the modules of the angular and linear velocities of the ball relative to the table.
4. Record the results of measurements and calculations in a notebook.
5. Answer the questions:

Measurement of the modulus of centripetal acceleration of a body with uniform motion in a circle

Instruments and materials are the same as in task 11.

Work order

1. Follow paragraphs. 1, 2 tasks 11.
2. Knowing the time of movement, the number of revolutions and the radius of rotation, calculate the module of centripetal acceleration of the ball.
3. Record the results of measurements and calculations in a notebook:
4. Answer the questions:

• How will the modulus of centripetal acceleration of the ball change if the number of its revolutions per unit time is doubled?
• How will the modulus of centripetal acceleration of the ball change if the radius of its rotation is doubled?

Observation of the dependence of the modules of the thread tension forces on the angle between them at a constant resultant force

Devices and materials: 1) a weight of 100 g with two hooks, 2) training dynamometers - 2 pcs., 3) a thread 200 mm long with loops at the ends.

Work order

• What is the modulus of the thread tension forces? Did they change during the experiment?
• What is the modulus of the resultant of the two tension forces in the threads? Did it change during the experiment?
• What can be said about the dependence of the modules of the thread tension forces on the angle between them at a constant resultant force?

Learning Newton's Third Law

Devices and materials: I) training dynamometers - 2 pcs., 2) a thread 200 mm long with loops at the ends.

Work order

• With what modulus force does the left dynamometer act on the right one? In which direction is this force directed? What dynamometer is it attached to?
• With what modulus force does the right dynamometer act on the left one? In which direction is this force directed? What dynamometer is it attached to?

3. Increase the interaction of dynamometers. Note their new testimony.

4. Connect the dynamometers with a thread and tighten it.

5. Answer the questions:

• With what modulus force does the left dynamometer act on the thread?
• With what modulus force does the right dynamometer act on the thread?
• With what force is the thread stretched modulo?

6. Draw a general conclusion from the experiments done.

Observation of the change in the modulus of the weight of a body moving with acceleration

Instruments and materials: 1) a training dynamometer, 2) a weight of 100 g with two hooks, 3) a thread 200 mm long with loops at the ends.

Work order

• Did the speed of the load change as it moved up and down?
• How did the modulus of the weight of the load change during its accelerated movement up and down?

4. Place the dynamometer on the edge of a table. Tilt the load to the side at a certain angle and release (Fig. 18). Watch the dynamometer reading as the load oscillates.

5. Answer the questions:

• Does the speed of the load change when it vibrates?
• Do the acceleration and weight of the load change when it vibrates?
• How do the centro-rapid acceleration and the weight of the load change with its oscillations?
• At what points of the trajectory is the centripetal acceleration and the weight of the load modulo the greatest, at which are the least? Figure 18.

Elucidation of the equilibrium conditions for a body with an axis of rotation under the action of forces on it

Devices and materials: 1) a sheet of cardboard measuring 150X 150 mm with two thread loops, 2) training dynamometers - 2 pcs., 3) a sheet of cardboard measuring 240X340 mm with a driven nail, 4) a student square, 5) a measuring ruler 30-35 cm with millimeter divisions, 6) pencil.

Work order

1. Put a sheet of cardboard on the nail. Hook the dynamometers on the loops, tension them with a force of approximately 2 and 3 N and position the loops at an angle of 100-120° to each other, as shown in Figure 27. Make sure that the cardboard sheet, when it deviates to the side, returns to the state

Rice. 27. Measure the modules of the applied forces (neglect the gravity of the cardboard).

2. Answer the questions:

• How many forces act on the cardboard?
• What is the modulus of the resultant force applied to the cardboard?

3. On a sheet of cardboard, draw straight line segments along which forces act, and using a square, build the shoulders of these forces, as shown in Figure 28.

4. Measure the force shoulders.

5. Calculate moments active forces and their algebraic sum. Under what condition is a body with a fixed axis of rotation in a state of equilibrium? Rice. 28. Write down the answer in a notebook.

Study of the Law of Conservation of Momentum in the Elastic Collision of Bodies

Devices and materials: 1) balls with a diameter of 25 mm - 2 pcs., 2) a thread 500 mm long, 3) a tripod for frontal work.

Work order

• What is the total momentum of the balls before the interaction?
• Did the balls acquire the same impulses modulo after the interaction?
• What is the total momentum of the balls after the interaction?

4. Release the retracted ball and note the deflection of the balls after impact. Repeat the experiment 2-3 times. Deviate one of the balls by 4-5 cm from the equilibrium position, and leave the second one alone.

5. Answer the questions in point 3.

6. Draw a conclusion from the experiments done

Measuring the efficiency of a moving block

Devices and materials: 1) a block, 2) a training dynamometer, 3) a measuring tape with centimeter divisions, 4) weights of 100 g each with two hooks - 3 pcs., 5) a tripod for frontal work, 6) a thread 50 cm long with loops at the ends.

Work order

1. Assemble the installation with the movable block, as shown in Figure 42. Throw the thread over the block. Hook one end of the thread to the foot of the tripod, the other to the hook of the dynamometer. Hang three weights weighing 100 g each from the block holder.
2. Take the dynamometer in your hand, place it vertically so that the block with the weights hangs on the threads, and measure the modulus of the thread tension.
3. Raise the weights evenly to a certain height and measure the displacement modules of the weights and the dynamometer relative to the table.
4. Calculate the useful and perfect work on the table.
5. Calculate the efficiency of the moving block.
6. Answer the questions:

• What gain in strength does the movable block give?
• Is it possible to get a gain in work with the help of a movable block?
• How to increase the efficiency of the moving block?

Application5

Requirements for the level of preparation of graduates of the basic school.

1. Own the methods of scientific knowledge.

1.1. Assemble installations for the experiment according to the description, drawing or scheme and conduct observations of the phenomena under study.

1.2. Measure: temperature, mass, volume, force (elasticity, gravity, sliding friction), distance, time interval, current strength, voltage, density, period of oscillation of the pendulum, focal length of the converging lens.

1.3. Present measurement results in the form of tables, graphs and identify empirical patterns:

• changes in body coordinates over time;
• elastic force from the elongation of the spring;
• current in the resistor from voltage;
• the mass of a substance from its volume;
• body temperature versus time during heat exchange.

1.4. Explain the results of observations and experiments:

• the change of day and night in the reference system associated with the Earth, and in the reference system associated with the Sun;
• high compressibility of gases;
• low compressibility of liquids and solids;
• processes of evaporation and melting of matter;
• evaporation of liquids at any temperature and its cooling during evaporation.

1.5. Apply experimental results to predict the values ​​of quantities characterizing the course of physical phenomena:

• the position of the body during its movement under the action of force;
• elongation of the spring under the action of a suspended load;
• current strength at a given voltage;
• the value of the temperature of the cooling water at a given point in time.

2. Own the basic concepts and laws of physics.

2.1. Give a definition of physical quantities and formulate physical laws.

2.2. Describe:

• physical phenomena and processes;
• changes and transformations of energy in the analysis: free fall of bodies, movement of bodies in the presence of friction, oscillations of a filament and spring pendulums, heating of conductors by electric current, melting and evaporation of a substance.

2.3. Calculate:

• the resultant force using Newton's second law;
• the momentum of the body, if the speed of the body and its mass are known;
• the distance over which sound propagates in a certain time at a given speed;
• kinetic energy of the body at a given mass and speed;
• the potential energy of the interaction of the body with the Earth and the force of gravity for a given body mass;
• the energy released in the conductor during the passage of an electric current (at a given current strength and voltage);
• energy absorbed (released) during heating (cooling) of bodies;

2.4. Construct an image of a point in a plane mirror and a converging lens.

3. Perceive, process and present educational information in various forms (verbal, figurative, symbolic).

3.1. Call:

• sources of electrostatic and magnetic fields, methods for their detection;
• energy conversion in internal combustion engines, electric generators, electric heaters.

3.2. Give examples:

• the relativity of the speed and trajectory of the same body in different frames of reference;
• change in the speed of bodies under the action of force;
• deformation of bodies during interaction;
• manifestation of the law of conservation of momentum in nature and technology;
• oscillatory and wave motions in nature and technology;
• environmental consequences of the operation of internal combustion engines, thermal, nuclear and hydroelectric power plants;
• experiments confirming the main provisions of the molecular kinetic theory.

3.4. Highlight the main idea in the text.

3.5. Find answers to questions in the text.

3.6. Review the text you have read.

3.7. Define:

• intermediate values ​​of quantities according to the tables of measurement results and constructed graphs;
• the nature of thermal processes: heating, cooling, melting, boiling (according to the graphs of changes in body temperature over time);
• resistance of a metal conductor (according to the oscillation schedule);
• according to the graph of the dependence of the coordinate on time: to the coordinate of the body at a given point in time; periods of time during which the body moved at a constant, increasing, decreasing speed; time intervals of the force.

3.8. Compare the resistance of metal conductors (more - less) according to the graphs of current versus voltage.

The meaning and types of independent experiment of students in physics. When teaching physics in high school, experimental skills are formed when performing independent laboratory work.

Teaching physics cannot be presented only in the form of theoretical classes, even if students are shown demonstration physical experiments in the classroom. To all types of sensory perception, it is necessary to add “work with hands” in the classroom. This is achieved when students perform a laboratory physical experiment, when they themselves assemble installations, measure physical quantities, and perform experiments. Laboratory studies arouse great interest among students, which is quite natural, since in this case the student learns about the world around him based on his own experience and his own feelings.

The significance of laboratory classes in physics lies in the fact that students form ideas about the role and place of the experiment in cognition. When performing experiments, students develop experimental skills, which include both intellectual and practical skills. The first group includes skills: to determine the purpose of the experiment, to put forward hypotheses, to select instruments, to plan an experiment, to calculate errors, to analyze results, to draw up a report on the work done. The second group includes skills: to assemble an experimental setup, to observe, measure, experiment.

In addition, the significance of a laboratory experiment lies in the fact that when it is performed, students develop such important personal qualities as accuracy in working with instruments; observance of cleanliness and order in the workplace, in the records that are made during the experiment, organization, perseverance in obtaining results. They form a certain culture of mental and physical labor.

In the practice of teaching physics at school, three types of laboratory classes have developed:

Frontal laboratory work in physics;

Physical workshop;

Home experimental work in physics.

Frontal laboratory work- this is the kind practical work when all students in the class simultaneously perform the same type of experiment using the same equipment. Frontal laboratory work is most often performed by a group of students consisting of two people, sometimes it is possible to organize individual work. Accordingly, the office should have 15-20 sets of instruments for frontal laboratory work. Total amount such devices will be about a thousand pieces. The names of frontal laboratory works are given in curricula. There are a lot of them, they are provided for almost every topic of the physics course. Before carrying out the work, the teacher reveals the preparedness of the students for the conscious performance of the work, determines with them its purpose, discusses the progress of the work, the rules for working with instruments, methods for calculating measurement errors. Frontal laboratory work is not very complex in content, is closely related chronologically to the material being studied and is usually designed for one lesson. Descriptions of laboratory work can be found in school textbooks in physics.

Physical workshop is carried out with the aim of repeating, deepening, expanding and generalizing the knowledge gained from various topics of the physics course; development and improvement of students' experimental skills through the use of more sophisticated equipment, more complex experiments; the formation of their independence in solving problems related to the experiment. The physical workshop is not connected in time with the material being studied, it is usually held at the end school year, sometimes - at the end of the first and second half of the year and includes a series of experiments on a particular topic. Students perform the work of a physical workshop in a group of 2-4 people using various equipment; in the following classes there is a change of work, which is done according to a specially drawn up schedule. When scheduling, take into account the number of students in the class, the number of workshops, the availability of equipment. Two academic hours are assigned to each work of the physical workshop, which requires the introduction of double lessons in physics into the schedule. This presents difficulties. For this reason, and due to the lack of necessary equipment, one-hour work of a physical workshop is practiced. It should be noted that two-hour work is preferable, since the work of the workshop is more difficult than frontal laboratory work, they are performed on more sophisticated equipment, and the proportion of students' independent participation is much larger than in the case of frontal laboratory work. Physical practicums are provided basically by programs of 9-11 classes. Approximately 10 hours of study time is allotted for each class. For each work, the teacher must draw up an instruction that should contain: name, purpose, list of instruments and equipment, a brief theory, a description of instruments unknown to students, a work plan. After completing the work, students must submit a report that should contain: the name of the work, the purpose of the work, a list of instruments, a diagram or drawing of the installation, a work execution plan, a table of results, formulas by which the values ​​\u200b\u200bof were calculated, calculation of measurement errors, conclusions. When evaluating the work of students in the workshop, one should take into account their preparation for work, a report on the work, the level of formation of skills, understanding theoretical material used methods of experimental research.

Home experimental work. Home laboratory work is the simplest independent experiment that is performed by students at home, outside of school, without direct control from the teacher over the progress of work.

The main tasks of this type of experimental work are:

Formation of the ability to observe physical phenomena in nature and in everyday life;

Formation of the ability to perform measurements with the help of measuring instruments used in everyday life;

Formation of interest in experiment and in the study of physics;

Formation of independence and activity.

Home laboratory work can be classified depending on the equipment used in their performance:

Works that use household items and improvised materials (measuring cup, tape measure, household scales, etc.);

Works in which home-made devices are used (lever scales, electroscope, etc.);

Work performed on industrial devices.

The classification is taken from .

In his book S.F. Pokrovsky showed that home experiments and observations in physics carried out by the students themselves: 1) make it possible for our school to expand the area of ​​connection between theory and practice; 2) develop students' interest in physics and technology; 3) awaken creative thought and develop the ability to invent; 4) accustom students to independent research work; 5) develop valuable qualities in them: observation, attention, perseverance and accuracy; 6) supplement classroom laboratory work with material that cannot be done in class in any way (a series of long-term observations, observation of natural phenomena, etc.), and 7) accustom students to conscious, purposeful work.

Home experiments and observations in physics have their own characteristics, being an extremely useful addition to class and general school practical work.

It has long been recommended that students have a home laboratory. it included, first of all, rulers, a beaker, a funnel, scales, weights, a dynamometer, a tribometer, a magnet, a watch with a second hand, iron filings, tubes, wires, a battery, a light bulb. However, despite the fact that very simple instruments are included in the set, this proposal has not been adopted.

To organize the home experimental work of students, you can use the so-called mini-laboratory proposed by the teacher-methodologist E.S. Obedkov, which includes many household items (penicillin bottles, rubber bands, pipettes, rulers, etc.), which is available to almost every student. E.S. Obyedkov developed a very big number interesting and useful experiences with this equipment.

It also became possible to use a computer to conduct a model experiment at home. It is clear that the corresponding tasks can only be offered to those students who have a computer and software and pedagogical tools at home.

For students to want to learn, it is necessary that the learning process is interesting for them. What are the students interested in? To get an answer to this question, we turn to excerpts from the article by I.V. Litovko, MOS (P) Sh No. 1 of Svobodny “Home experimental tasks as an element of students' creativity”, published on the Internet. Here is what I.V. Litovko:

“One of the most important tasks of the school is to teach students how to learn, to strengthen their ability for self-development in the process of education, for which it is necessary to form appropriate stable desires, interests, and skills in schoolchildren. An important role in this is played by experimental tasks in physics, which in their content represent short-term observations, measurements and experiments that are closely related to the topic of the lesson. The more observations of physical phenomena, experiments the student makes, the better he will master the material being studied.

To study the motivation of students, they were offered next questions and the results are:

What do you like about studying physics ?

a) problem solving -19%;

b) demonstration of experiments -21%;

FEDERAL STATE GENERAL EDUCATIONAL INSTITUTION SECONDARY EDUCATIONAL SCHOOL

NAME a. n. RADISHCHEVA

Kuznetsk - 12

EXPERIMENTAL TASKS IN PHYSICS

1. Measurement of the modulus of initial velocity and deceleration time of a body moving under the action of friction force

Devices and materials: 1) a bar from a laboratory tribometer, 2) training dynamometer, 3) measuring tape with centimeter divisions.

1. Place the block on the table and note its initial position.

2. Push the bar lightly with your hand and notice its new position on the table (see fig.).

3. Measure the stopping distance of the bar relative to the table._________

4. Measure the modulus of the bar's weight and calculate its mass.__

5. Measure the modulus of sliding friction force of the bar on the table._______________________________________________________________

6. Knowing the mass, braking distance and sliding friction modulus, calculate the initial velocity modulus and the braking time of the bar.______________________________________________

7. Write down the results of measurements and calculations.__________

2. Measurement of the modulus of acceleration of a body moving under the action of forces of elasticity and friction

Devices and materials: 1) laboratory tribometer, 2) training dynamometer with lock.

Work order

1. Measure the weight modulus of the bar using a dynamometer._______

_________________________________________________________________.

2. Hook the dynamometer onto the block and place them on the tribometer ruler. Set the pointer of the dynamometer to the zero division of the scale, and the latch - near the stop (see Fig.).

3. Move the bar uniformly along the tribometer ruler and measure the sliding friction modulus. ________

_________________________________________________________________.

4. Bring the bar into accelerated motion along the ruler of the tribometer, acting on it with a force greater than the modulus of the sliding friction force. Measure the modulus of this force. __________________

_________________________________________________________________.

5. Based on the data obtained, calculate the acceleration modulus of the bar._

_________________________________________________________________.

__________________________________________________________________

2. Move the bar with weights evenly along the tribometer ruler and record the dynamometer readings to the nearest 0.1 N.________________________________________________________________.

3. Measure the displacement module of the bar with an accuracy of 0.005 m

regarding the table. ___________________________________________.

__________________________________________________________________

5. Calculate the absolute and relative errors of work measurement._______________________________________________

__________________________________________________________________

6. Write down the results of measurements and calculations.__________

__________________________________________________________________

_________________________________________________________________

Answer the questions:

1. How is the traction force vector directed relative to the bar displacement vector? _____________________________________________

_________________________________________________________________.

2. What is the sign of the work done by the traction force to move the bar? ____________________________________________

__________________________________________________________________

Option 2.

1. Place the bar with two weights on the tribometer ruler. Hook the dynamometer onto the hook of the bar, placing it at an angle of 30 ° to the ruler (see Fig.). Check the angle of the dynamometer with a square.

2. Move the bar with weights evenly along the ruler, maintaining the original direction of the traction force. Record the dynamometer readings to the nearest 0.1 N.____________________

_________________________________________________________________.

3. Measure the module of movement of the bar with an accuracy of 0.005 m relative to the table._______________________________________________

4. Calculate the work of the traction force to move the bar relative to the table. _______________________________________________

__________________________________________________________________

__________________________________________________________________.

5. Write down the results of measurements and calculations.__________

__________________________________________________________________

Answer the questions:

1. How is the traction force vector directed relative to the bar displacement vector? ____________________________________________

_________________________________________________________________.

2. What is the sign of the work of the traction force in moving the bar?

_________________________________________________________________.

_________________________________________________________________

4. Measurement of the efficiency of the movable block

Prigs and materials: 1) a block, 2) a training dynamometer, 3) a measuring tape with centimeter divisions, 4) weights of 100 g each with two hooks - 3 pcs., 5) a tripod with a foot, 6) a thread 50 cm long with loops at the ends.

Work order

1. Assemble the unit with the moving block as shown in the figure. Throw the thread over the block. Hook one end of the thread to the foot of the tripod, the other to the hook of the dynamometer. Hang three weights weighing 100 g each from the block holder.

2. Take the dynamometer in your hand, place it vertically so that the block with weights hangs on the threads, and measure the modulus of the thread tension force._____________

___________________________________________

3. Raise the weights evenly to a certain height and measure the displacement modules of the weights and the dynamometer relative to the table. _______________________________________________________________

_________________________________________________________________.

4. Calculate the useful and perfect work relative to the table. _______________________________________________________________

__________________________________________________________________

5. Calculate the efficiency of the moving block. ________________________

Answer the questions:

1. What gain in strength does the movable block give?______________

2. Is it possible to get a gain in work with the help of a movable block? _______________________________________________

_________________________________________________________________

3. How to increase the efficiency of the movable block?_____________________

____________________________________________________________________________________________________________________________________________________________________________________________________.

5. Measuring the moment of force

Prigs and materials: 1) laboratory trough, 2) training dynamometer, 3) measuring tape with centimeter divisions, 4) loop made of strong thread.

Work order

1. Put a loop on the end of the chute and hook it with a dynamometer as shown in the figure. While lifting the dynamometer, turn the chute around a horizontal axis passing through its other end.

2.Measure the modulus of force required to rotate the chute._

3.Measure the arm of this force. ________________________________.

4. Calculate the moment of this force.______________________________

__________________________________________________________________.

5. Move the loop to the middle of the chute, and again measure the modulus of force required to rotate the chute and its shoulder.______

___________________________________________________________________________________________________________________________________.

6. Calculate the moment of the second force. ___________________________

_________________________________________________________________.

7. Compare the calculated moments of forces. Make a conclusion. _____

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________.

6. “Measuring the stiffness of the spring.

Objective: find the stiffness of the spring.

materials: 1) tripod with clutches and foot; 2) coil spring.

Work order:

Fix the end of the spiral spring on the tripod (the other end of the spring is equipped with an arrow - pointer and a hook).

Install and secure a ruler with millimeter divisions next to or behind the spring.

Mark and write down the division of the ruler against which the spring pointer falls. __________________________

Hang a weight of known mass from the spring and measure the extension of the spring caused by it.________________________________

___________________________________________________________________

To the first load, add the second, third, etc. weights, each time recording the extension / x / of the spring. According to the measurement results, fill in the table _________________________________

___________________________________________________________________

__________________________________________________________________.

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_______________________________________________________________.

3. Weigh the bar and weight.______________________________________

________________________________________________________________.

4. To the first weight, add the second, third weights, each time weighing the bar and weights and measuring the friction force. _______________

____________________________________________________________________________________________________________________________________________________________________________________________.

5. Based on the measurement results, build a graph of the dependence of the friction force on the pressure force and, using it, determine the average value of the friction coefficient μ cf. ______________________________-

_____________________________________________________________________________________________________________________________________________________________________________________________________.

Laboratory work

Spring stiffness measurement

Objective: find the stiffness of the spring by measuring the elongation of the spring when balancing the gravity of the load with the force of the elasticity of the spring and plot the dependence of the elastic force of this spring on its elongation.

Equipment: a set of cargoes; ruler with millimeter divisions; tripod with clutch and foot; spiral spring (dynamometer).

Questions for self-study

1. How to determine the force of gravity of the load?_________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

4. The weight hangs motionless on the spring. What can be said in this case about the force of gravity of the load and about the force of elasticity of the spring? _________

__________________________________________________________________

__________________________________________________________________

5. How can the spring rate be measured with this equipment? _______________________________________________

__________________________________________________________________

__________________________________________________________________

6. How, knowing the stiffness, plot the dependence of the elastic force on the elongation of the spring? ________________________________

__________________________________________________________________

__________________________________________________________________

Note. Take the free fall acceleration equal to (10 ± 0.2) m/s2, the mass of one load (0.100 ± 0.002) kg, the mass of two loads - (0.200 ± 0.004) kg, etc. It is enough to make three experiments.

Laboratory work

"Measuring the coefficient of sliding friction"

Objective: determine the coefficient of friction.

Materials: 1) wooden block; 2) wooden ruler; 3) a set of goods.

Work order

Lay the block on a horizontal wooden ruler. Place a load on the block.

Having attached a dynamometer to the bar, pull it as evenly as possible along the ruler. Note the dynamometer reading. ____________________________________________________

__________________________________________________________________

Weigh the bar and the load. _______________________________________________

Add the second, third weights to the first weight, each time weighing the bar and weights and measuring the friction force._________________

_________________________________________________________________

_________________________________________________________________

According to the measurement results, fill in the table:

5. Based on the measurement results, plot the dependence of the friction force on the pressure force and, using it, determine the average value of the friction coefficient μ. ________________________________

__________________________________________________________________

__________________________________________________________________

6. Draw a conclusion.

Laboratory work

Study of capillary phenomena caused by the surface tension of a liquid.

Objective: measure the average diameter of the capillaries.

Equipment: a vessel with tinted water, a strip of filter paper measuring 120 x 10 mm, a strip of cotton fabric measuring 120 x 10 mm, a measuring ruler.

The wetting liquid is drawn into the capillary. The rise of the liquid in the capillary occurs until the resulting force acting upwards on the liquid, Fv, is balanced by the gravity mg of the liquid column of height h:

According to Newton's third law, the force Fv acting on the liquid is equal to the surface tension force Fpov acting on the capillary wall along the line of contact with the liquid:

Thus, at equilibrium of the liquid in the capillary (Figure 1)

Fsurf = mg. (one)

We will assume that the meniscus has the shape of a hemisphere, the radius of which r is equal to the radius of the capillary. The length of the contour that bounds the surface of the liquid is equal to the circumference:

Then the surface tension force is:

Fsurf = σ2πr, (2)

where σ is the surface tension of the liquid.

picture 1

The mass of the liquid column with volume V = πr2h is:

m = ρV = ρ πr2h. (3)

Substituting expression (2) for Fsurf and mass (3) into the equilibrium condition of the liquid in the capillary, we obtain

σ2πr = ρπr2hg,

where is the diameter of the capillary

D = 2r = 4σ/ρgh. (4)

The order of the work.

With strips of filter paper and cotton cloth, simultaneously touch the surface of the tinted water in the glass (Figure 2), observing the rise of water in the strips.

As soon as the rise of water stops, remove the strips and measure the heights h1 and h2 of the rise of water in them with a ruler.

The absolute measurement errors Δ h1 and Δ h2 are taken equal to twice the division price of the ruler.

Δ h1 = 2 mm; Δh2 = 2 mm.

Calculate the capillary diameter using formula (4).

D2 = 4σ/ρgh2.

For water σ ± Δσ = (7.3 ± 0.05)х10-2 N/m.

Calculate the absolute errors Δ D1 and Δ D2 for indirect measurement of the capillary diameter.

figure 2

∆D1 = D1(∆σ/ σ + ∆h1/ h1);

∆D2 = D2(∆σ/ σ + ∆h2/ h2).

The errors Δ g and Δ ρ can be neglected.

Present the final result of capillary diameter measurement as