Experimental and theoretical physics. Physics is an experimental science
Experimental physics - Shutov V.I.., Sukhov V.G., Podlesny D.V.. - 2005
The experimental work included in the program of physics and mathematics lyceums as part of a physics workshop is described. The manual is an attempt to create a unified guide for conducting practical classes in classes and schools with in-depth study of physics, as well as for preparation for experimental rounds of olympiads high level.
Introductory material is traditionally devoted to methods of processing experimental data. The description of each experimental work begins with a theoretical introduction. The experimental part contains descriptions of experimental setups and tasks that regulate the sequence of students’ work when carrying out measurements. Samples of worksheet for recording measurement results, recommendations on methods for processing and presenting results, and requirements for reporting are provided. At the end of the descriptions there are suggested test questions, the answers to which students must prepare to defend their work.
For schools and classes with in-depth study of physics.
Introduction.
Errors physical quantities. Processing of measurement results.
Practical work 1. Measuring the volume of bodies correct form.
Practical work 2. Study of the rectilinear motion of bodies in the field of gravity using an Atwood machine.
Practical work 3. Dry friction. Determination of sliding friction coefficient.
Theoretical introduction to work on oscillations.
Practical work 4. Study of oscillations of a spring pendulum.
Practical work 5. Study of oscillations of a mathematical pendulum. Determination of free fall acceleration.
Practical work 6. Study of oscillations of a physical pendulum.
Practical work 7. Determination of the moments of inertia of bodies of regular shape using the method of torsional vibrations.
Practical work 8. Study of the laws of rotation solid on a cruciform Oberbeck pendulum.
Practical work 9. Determination of the ratio of molar heat capacities of air.
Practical work 10. Standing waves. Measuring wave speed in an elastic string.
Practical work 11. Determination of the ratio ср/с ι? for air in a standing sound wave.
Practical work 12. Study of the operation of an electronic oscilloscope.
Practical work 13. Measuring the frequency of oscillations by studying Lissajous figures.
Practical work 14. Determination of resistivity of nichrome wire.
Practical work 15. Determination of conductor resistance using the Wheatstone compensation method.
Practical work 16. Transient processes in a capacitor. Determination of capacity.
Practical work 17. Determination of tension electric field in a cylindrical conductor carrying current.
Practical work 18. Study of the operation of a source in a direct current circuit.
Practical work 19. Study of the laws of reflection and refraction of light.
Practical work 20. Definition focal lengths converging and diverging lenses.
Practical work 21. The phenomenon of electromagnetic induction. Study magnetic field solenoid.
Practical work 22. Study of damped oscillations.
Practical work 23. Study of the phenomenon of resonance in an alternating current circuit.
Practical work 24. Fraunhofer diffraction by a slit. Measuring the slit width using the “wave method”.
Practical work 25. Fraunhofer diffraction. Diffraction grating as an optical device.
Practical work 26. Determination of the refractive index of glass using the “wave” method.
Practical work 27. Determination of the radius of curvature of a lens in an experiment with Newton’s rings.
Practical work 28. Study of polarized light.
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Physics - experimental science. In the works of Galileo, Newton and other researchers, its main method was established: any prediction of the theory must be confirmed by experience. In the XVII, XVIII and even XIX centuries. the same people carried out theoretical analysis, and tested their conclusions themselves experimentally. But in the 20th century. The rapid accumulation of knowledge, the development of technology, everything that is called the scientific and technological revolution, led to the fact that it became impossible for one person to create theories and carry out experiments.
There was a division of physicists into theorists and experimentalists. Of course, there are no rules without exceptions, and sometimes theorists conduct experiments, and experimenters do theory. But every year there are fewer and fewer such exceptions.
Now experimenters have complex and powerful equipment in their hands: accelerators, nuclear reactors, ultra-high vacuum technology, deep cooling and, of course, electronics. It has completely transformed the possibilities of experience, and this can be illustrated by this example.
At the beginning of this century, E. Rutherford and his collaborators recorded alpha particles in their experiments using a zinc sulfide screen and a microscope. As each particle hit the screen, the screen produced a faint flash of light that could be seen through a microscope. Before starting the experiment, the researchers had to sit in the dark for hours to sharpen the sensitivity of the eyes. The maximum number of pulses that could be counted was two or three per second. After a few minutes my eyes got tired.
And now special electronic devices - photomultipliers - are able to distinguish and transform much weaker light flashes into electrical impulses. They manage to count tens and hundreds of thousands of pulses per second. And not just count. Special circuits, using the shape of an electrical pulse (repeating a light one), provide information about energy, charge, even the type of particle. This information is stored and processed by high-speed computers.
It should be noted that experimental physics has a dual relationship with technology. On the one hand, physics, discovering still unknown areas, such as electricity, atomic energy, lasers, gradually masters them and transfers them into the hands of engineers. On the other hand, after technology has created the appropriate devices and even new industries, experimental physics begins to use these devices when setting up experiments. And this allows her to penetrate deeper into the secrets of matter.
Modern means conducting an experiment requires the participation of a whole team of experimenters.
The experimental study can be divided into three parts: preparation, measurement, and processing of results.
When the idea of experience is born, the possibility of its implementation, creation, becomes on the agenda. new installation or reworking an old one. At this stage it is necessary to exercise maximum caution.
“I have always attached great importance to the way the experience was conceived and staged. Of course, we must proceed from a certain, pre-thought-out idea; but whenever possible, experience should leave the maximum number of windows open so that an unforeseen phenomenon can be observed,” wrote the outstanding French physicist F. Joliot-Curie.
When designing and manufacturing the installation, specialized specialists come to the aid of the experimenter. design bureaus, workshops, sometimes large factories. Ready-made devices and blocks are widely used. Nevertheless, the most important work falls to physicists: the creation of those units that are unique and which have sometimes never been used anywhere else. Therefore, outstanding experimental physicists have always been very good engineers.
When the installation is assembled, it is time to conduct control experiments. Their results serve to check the performance of the equipment and determine its characteristics.
And then the main measurements begin, which can sometimes last for a very long time. A kind of record was set when recording solar neutrinos - measurements lasted 15 years.
Processing the results is also far from simple. There are areas of experimental physics in which the center of gravity of all experience is concentrated on processing, for example image processing, obtained in a bubble chamber. The cameras are installed in the path of beams from the world's largest accelerators. In them, a chain of bubbles is formed on the trail of a flying particle. The trail becomes visible and can be photographed. The camera produces tens of thousands of photos per day. Until recently (and now automation has come to the rescue) hundreds of laboratory assistants sat at viewing tables at projection microscopes, making the initial selection of photographs. Then automated installations and computers came into operation. And after all this, the researchers received the necessary information, could build graphs, and make calculations.
Soviet experimenters have something to be proud of. Before the revolution, there were only a few dozen seriously working physicists in Russia. Most of them conducted research in unsuitable premises and with homemade instruments. Therefore, the world-class discoveries made by P. N. Lebedev (light pressure), A. G. Stoletov (research on the photoelectric effect) can be called a real feat.
Our experimental physics was founded in the difficult conditions of the first years Soviet power. It was created through the efforts of such scientists as A.F. Ioffe, S.I. Vavilov and a number of others. They were experimenters, teachers, and organizers of science. Their students and the students of their students glorified Russian physics. Vavilov-Cherenkov radiation (see Vavilov-Cherenkov effect), superfluidity, Raman scattering of light, lasers - listing only the largest discoveries of Soviet scientists could take many pages.
The development of experimental physics is not like a smooth and well-worn road. Through the labor of many people, observations are accumulated, experiments and calculations are made. But sooner or later the gradual growth of our knowledge undergoes a sharp leap. There is a discovery. Much of what everyone is so accustomed to appears in a completely different light. And we need to supplement, redo, sometimes create anew the theory, hastily carry out new experiments.
Therefore, many outstanding scientists compared the path of science to a road in the mountains. It does not go in a straight line, forcing travelers to climb steep slopes, sometimes retreating back to eventually reach the top. And then, from the vanquished heights, new peaks and new paths open up.
Physics is an experimental science. An experiment is understood as experience, i.e., observation of the phenomenon under study under the conditions taken into account, allowing one to monitor its progress and recreate it each time the same conditions are repeated. Therefore, understanding and consciousness of physical theory is impossible without confirmed data, that is, without experiment. It assumes an active independent position of students in learning; development of general educational skills and abilities: primarily research and self-assessment; Formation of skills that are associated with experience, their application in practical activities, priority targeting at the development of students’ cognitive interest, implementation of the principle of connecting learning with life.
For many students, the physics material presented in books and textbooks remains incomprehensible for a long time. And interest in this subject due to misunderstanding, it decreases, which leads to a lack of understanding of the subject and a decrease in academic performance.
How to awaken students' thirst for knowledge? How to revive the learning process, how to create an atmosphere of joyful elation that accompanies search and creativity? How to make learning activities cheerful, exciting and interesting.
It will help to solve these issues when teaching physics by placing the student in the conditions of a researcher, in the place of a scientist or discoverer.
For a student, observations and experiments, and the organization of research activities when studying physics are a necessary factor to increase interest in physical science, make it exciting, entertaining and useful and realize that physics is not scary, physics is interesting.
It is the experiment that helps the student not only better understand the theory, but also actively participate in the work in the lesson, put forward his own theories to solve the problem, solve not only the assigned problems together with the teacher, but even independently. Experimentation is an important aspect of practice. With its help, science is able not only to explain the phenomena of the material world, but also to directly master them. Therefore, experiment is one of the main means of connecting science with life.
An experiment is simultaneously a source of knowledge, a teaching method, and a means of activating a student’s cognitive activity. 
It is performed for the whole class. A significant part of students, especially boys, have an early awakened interest in technology in general. Therefore, the appearance on the demonstration table of any technical devices in the form of instruments of a demonstration experiment attracts their attention.
For successful research activities, it is necessary to develop students' skills in working with their own hands and arouse interest in research work.
It is important that students learn:
Set a goal;
Draw up a research plan;
Select the necessary equipment and materials;
Assemble the necessary installations;
Conduct research and formulate conclusions
Psychologists note that complex visual material is remembered better than its description. Therefore, the demonstration of experiments is captured better than the teacher’s story about physical experience.
In the practice of teaching physics at school, three types of experimental classes have developed:
Physical workshop;
Home experimental work in physics.
Let's focus on home experiments in physics.
Today in the field of education, new criteria for assessing the quality of education are gaining momentum, taking into account the dynamics of the development of each student. This is due to the increasing speed of change in society: states, technologies, lifestyles are changing, new products and needs appear, forms of work are changing. The most successful people are those who can create a unique product or service in a limited time, adapt and master new methods of work, offer an extraordinary way out of a problem situation, that is, implement certain competencies. The need to quickly find solutions to emerging production and scientific problems has led to the spread of independent activity as a technology for solving problems. It is clear that successful specialists can only be obtained if they are trained from school. As a result, independent activity of students will irreversibly become one of the most important forms of modern education.
When conducting a demonstration experiment in a classroom, the time allocated for the experiment is limited to the duration of the lesson, and in fact even less. In this case, the main activity is performed by the teacher and, at best, one or two students. The rest only observe the experiment. Often after a lesson in which a demonstration was given, many children come to the teacher’s table wanting to turn the handle of the generator, touch a glass of water to determine its temperature, and so on. All this shows that many children want to experiment on their own, it’s interesting to them! Teachers always try (if they are good teachers, of course) to teach in such a way that children find it interesting. And here you don’t need to look for anything - the children themselves give a hint that they are not averse to experimenting themselves, to see the phenomena that the teacher talked about in theory, in practice.
What happens if the teacher invites students to perform an experiment or conduct an observation outside of school, that is, at home or on the street? Nowadays, advanced research requires huge funds, which even some countries do not always have. Thus, home-based experiments should not require the use of any equipment or significant material costs. It may seem that the scientific value of such experiments is very small. But is it bad if a child himself can check a law or phenomenon discovered many years before him? Experience is a creative task; doing something on your own, the student, whether he wants it or not, will think about how easier it is to carry out the experiment, where he has encountered a similar phenomenon in practice, where else this phenomenon may be useful. What should be noted here is that children learn to distinguish physical experiments from all sorts of tricks, do not confuse one with the other.
What does a child need to conduct the experiment at home? First of all, this is probably a fairly detailed description of the experience, indicating the necessary items, where it is said in a form accessible to the child what needs to be done and what to pay attention to. In school physics textbooks at home, it is suggested that you either solve problems or answer questions posed at the end of the paragraph. There you can rarely find a description of an experience that is recommended for schoolchildren to conduct independently at home. Therefore, if a teacher asks students to do something at home, then he is obliged to give them detailed instructions. The experiment should not require any significant material costs from the student; when conducting the experiment, objects and substances that are found in almost every home should be used: dishes, jars, bottles, water, salt, and so on. An experiment performed at home by schoolchildren should be simple in execution and equipment, but, at the same time, be valuable in the study and understanding of physics in childhood, and be interesting in content.
The main objectives of the home experiment:
Formation of the ability to observe physical phenomena in nature and in everyday life;
Formation of the ability to carry out measurements using measuring instruments used in everyday life;
Formation of interest in experiments and in the study of physics;
Formation of independence and activity.
Homemade laboratory work can be classified depending on the equipment used in their implementation:
Works that use household items and available materials (measuring cup, tape measure, household scales, etc.);
Works in which homemade instruments are used (lever scales, electroscope, etc.);
Work performed on devices produced by industry.
The home experiment can be assigned after completing the topic in class. Then the students will see with their own eyes and be convinced of the validity of the theoretically studied law or phenomenon. At the same time, the knowledge obtained theoretically and tested in practice will be quite firmly embedded in their consciousness.
Or vice versa, you can set a homework task, and after completing it, explain the phenomenon. Thus, it is possible to create a problematic situation for students and move on to problem-based learning, which involuntarily gives rise to students’ cognitive interest in the material being studied, ensures students’ cognitive activity during learning, and leads to the development of students’ creative thinking. In this case, even if schoolchildren cannot explain the phenomenon they saw at home themselves, they will listen with interest to the teacher’s story.
Examples of home experiments in physics:
Friction.
1. Take a long, heavy book, tie it with a thin thread and
attach a rubber thread 20 cm long to the thread. Place the book on the table and very slowly begin to pull the end of the rubber thread. Try to measure the length of the stretched rubber thread as the book begins to slide. Measure the length of the stretched book while moving the book evenly. Place two thin cylindrical pens (or two cylindrical pencils) under the book and pull the end of the thread in the same way. Measure the length of the stretched thread when the book moves evenly on the rollers. Compare the three results obtained and draw conclusions. Note. The next task is a variation of the previous one. It is also aimed at comparing static friction, sliding friction and rolling friction.
2. Place a hexagonal pencil on the book parallel to its spine. Slowly lift the top edge of the book until the pencil begins to slide down. Slightly reduce the tilt of the book and secure it in this position by placing something under it. Now the pencil, if you put it on the book again, will not move. It is held in place by a frictional force - the static friction force. But if this force is slightly weakened - and for this it is enough to click your finger on the book - and the pencil will crawl down until it falls on
table. (The same experiment can be done, for example, with a pencil case, matchbox, eraser, etc.). Think about why it is easier to pull a nail out of a board if you rotate it around its axis? To move a thick book on the table with one finger, you need to apply some force. And if you put two round pencils or pens under the book, which in this case will be roller bearings, the book will easily move with a weak push with your little finger. Carry out experiments and compare the static friction force, the sliding friction force and the rolling friction force.
3. In this experiment, two phenomena can be observed at once: inertia, experiments with
which will be described further, and friction. Take two eggs: one raw and the other hard-boiled. Place both eggs on a large plate. You see that boiled egg behaves differently than raw: it rotates much faster. In a boiled egg, the white and yolk are rigidly connected to their shell and to each other because they are in a solid state. And when we spin raw egg, then we first spin only the shell, only then, due to friction, layer by layer the rotation is transferred to the white and yolk. Thus, the liquid white and yolk, by their friction between the layers, slow down the rotation of the shell. Note. Instead of raw and boiled eggs, you can twist two pans,
one of which contains water, and the other contains the same volume of cereal.
Gas pressure. Atmospheric pressure.
1. Rinse the plastic bottle hot water and close the lid tightly. As the air cools down to room temperature, the pressure inside drops, atmospheric pressure squeezes the bottle from the sides. Why?
2. Model of lung function. Cut off the bottom of a plastic bottle. Pull the balloon over the neck and push it inside. Cover the cut part of the bottle with film from another balloon or from a used rubber glove and secure it with tape. When the film is pulled back, the volume of air inside the bottle increases, the pressure decreases and becomes less than atmospheric pressure, and the ball inflates. When you press on the bottom film, the volume of air in the bottle decreases, the pressure becomes greater than atmospheric pressure, and the ball contracts.
3. Inflate the balloon. What properties of the gas and the shell of the ball are indicated by its shape. Why, by directing a stream of air in a certain direction, do we make the balloon inflate in all directions at once? Why aren't all balloons spherical?
4. Using a tube or straw and a soap solution, get bubble. Explain why a soap bubble separated from a tube has a spherical shape.
5. Construct a Cartesian diver using plastic bottle or a 3-liter jar with a plastic lid. Make a float from an ordinary transparent bottle, for example a penicillin bottle, filling it with water to more than 1/3 of the volume. Make a hole in the bottle stopper with an awl and tightly insert a 10mm long tube from the ballpoint pen into it. You can take a pipette and fill it with water so that it floats vertically, almost completely submerged in water. After filling the bottle (jar) with water, lower the float into it. When you press the lid of the jar or press on the bottle, the float lowers. Monitor the volume of water in the float as it sinks and rises. The float can be made from a cap from a felt-tip pen or from a ballpoint pen. To make the cap float vertically, insert several paper clips into it. You can make a “propeller” out of foil and put it on the cap, then the diver will lower and rise, rotating.
6. Hold a lit candle or paper inside a glass turned upside down. Then quickly place the glass upside down on the surface of the inflated balloon. Describe the observed phenomena.
Conclusion.
Thus, if teachers use home experimental tasks in their work, this will have a positive impact on the process of teaching students physics and on their general development, the result of training will be the development of versatile, original, unfettered thinking. A is the path to the development of high intellectual activity of students. Students will not only be able to truly understand many of the processes taking place around them, but most importantly, apply the acquired knowledge and experience in their lives.
References.
Favorites. - Chelyabinsk: ChSPU, 2000. . Activation cognitive activity students when studying physics. - Moscow: Education, 1983. . Activating students' thinking in physics lessons. - Moscow: Education, 1980. Methods of teaching physics in grades 7-8 of secondary school. // Ed. . - Moscow: Education, 1990. Internet resources.
There are several branches of physics, and therefore there are several times more scientists than in other sciences. You can study theoretical, experimental, or applied physics. It all depends on the desire of the scientist and his knowledge.
A few words about experimental physics. Why is it called that? Does it involve conducting experiments? Of course yes. This is a certain way of studying and knowing nature, which consists in the process of studying various natural phenomena in conditions that are specially prepared and prepared in advance. The most important difference from theoretical physics is that experimental physics does not study mathematical models of nature, as theoretical physics does, but nature itself, its essence.
Just like lawyer in arbitration proceedings can easily change the course of the entire process if he has special knowledge, and a simple disagreement with the obtained result of an experiment will be the main criterion for an error in the theory of physics. In other words, simply not applicable to our world. But a statement that is the opposite of this will nevertheless not be true: if the scientist agrees with the experiments, this will not be proof of the correctness of the given theory, as well as its application. So, the most main criterion the viability of a physics theory is to test it with experiment. This is what experimental physics is for.
It would seem that the role of experiment is more than obvious. But it was discovered only by Galileo and the researchers who worked after him. It was they who made their conclusions about the characteristics of the world, based on their observations of the behavior of various objects in specially created conditions. In other words, they were conducting experiments. By the way, this approach is completely opposite to the approach of the Greeks: they believed that their thoughts about the structure of the world were true and correct, and experience was considered just a confirmed deception, that is, it could not claim to receive true knowledge.
In the very ideal experimental physics is obliged to give only detailed descriptions experiments and their results, without their interpretation. But in practice this is unrealistic. After all, scientists have ideas about how certain objects behave, that is, these ideas are based on the interpretation of the results obtained.
So, experimental physics is not only a very important part general physics, but also quite interesting, because observations of the behavior of various objects in different artificial conditions arouse interest not only among scientists, but also among ordinary people.
Tens and hundreds of thousands of physical experiments have been carried out over the thousand-year history of science. It’s not easy to select a few of the “best” to talk about. What should be the selection criterion?
Four years ago, The New York Times published an article by Robert Creese and Stoney Book. It described the results of a survey conducted among physicists. Each respondent had to name the ten most beautiful physical experiments in the history of physics. In our opinion, the criterion of beauty is in no way inferior to other criteria. Therefore, we will talk about the experiments that were included in the top ten according to the results of the Kreese and Book survey.
1. Experiment of Eratosthenes of Cyrene
One of the oldest known physical experiments, as a result of which the radius of the Earth was measured, was carried out in the 3rd century BC by the librarian of the famous Library of Alexandria, Erastothenes of Cyrene.
The experimental design is simple. At noon, at day summer solstice, in the city of Siena (now Aswan) the Sun was at its zenith and objects did not cast shadows. On the same day and at the same time, in the city of Alexandria, located 800 kilometers from Siena, the Sun deviated from the zenith by approximately 7°. This is approximately 1/50 of a full circle (360°), which means that the circumference of the Earth is 40,000 kilometers and the radius is 6,300 kilometers.
It seems almost incredible that such a measured simple method The radius of the Earth turned out to be only 5% less than the value obtained by the most accurate modern methods.
2. Galileo Galilei's experiment
In the 17th century, the dominant point of view was Aristotle, who taught that the speed at which a body falls depends on its mass. The heavier the body, the faster it falls. Observations that each of us can make in everyday life, would seem to confirm this.
Try to release at the same time light hands a toothpick and a heavy stone. The stone will touch the ground faster. Such observations led Aristotle to the conclusion about the fundamental property of the force with which the Earth attracts other bodies. In fact, the speed of falling is affected not only by the force of gravity, but also by the force of air resistance. The ratio of these forces for light objects and for heavy ones is different, which leads to the observed effect. The Italian Galileo Galilei doubted the correctness of Aristotle's conclusions and found a way to test them. To do this, he dropped a cannonball and a much lighter musket bullet from the Leaning Tower of Pisa at the same moment. Both bodies had approximately the same streamlined shape, therefore, for both the core and the bullet, the air resistance forces were negligible compared to the forces of gravity.
Galileo found that both objects reach the ground at the same moment, that is, the speed of their fall is the same. Results obtained by Galileo. - consequence of the law universal gravity and the law according to which the acceleration experienced by a body is directly proportional to the force acting on it and inversely proportional to the mass.
3. Another Galileo Galilei experiment
Galileo measured the distance that balls rolling on an inclined board covered in equal intervals of time, measured by the author of the experiment using a water clock. The scientist found that if the time was doubled, the balls would roll four times further. This quadratic relationship meant that the balls moved at an accelerated rate under the influence of gravity, which contradicted Aristotle's assertion, which had been accepted for 2000 years, that bodies on which a force acts move at a constant speed, whereas if no force is applied to the body, then it is at rest.
The results of this experiment by Galileo, like the results of his experiment with the Leaning Tower of Pisa, later served as the basis for the formulation of the laws of classical mechanics.
4. Henry Cavendish's experiment
After Isaac Newton formulated the law of universal gravitation: the force of attraction between two bodies with masses Mit, remote friend from each other at a distance r, equal to F=G(mM/r2), it remained to determine the value of the gravitational constant G. To do this, it was necessary to measure the force of attraction between two bodies with known masses. This is not so easy to do, because the force of attraction is very small.
We feel the force of gravity of the Earth. But it is impossible to feel the attraction of even a very large mountain nearby, since it is very weak. A very subtle and sensitive method was needed. It was invented and used in 1798 by Newton's compatriot Henry Cavendish. He used a torsion scale - a rocker with two balls suspended on a very thin cord. Cavendish measured the displacement of the rocker arm (rotation) as other balls of greater mass approached the scales.
To increase sensitivity, the displacement was determined by light spots reflected from mirrors mounted on the rocker balls. As a result of this experiment, Cavendish was able to quite accurately determine the value of the gravitational constant and, for the first time, calculate the mass of the Earth.
5. Jean Bernard Foucault's experiment
French physicist Jean Bernard Leon Foucault experimentally proved the rotation of the Earth around its axis in 1851 using a 67-meter pendulum suspended from the top of the dome of the Parisian Pantheon. The swing plane of the pendulum remains unchanged in relation to the stars. An observer located on the Earth and rotating with it sees that the plane of rotation is slowly turning in the direction opposite to the direction of rotation of the Earth.
6. Isaac Newton's experiment
In 1672, Isaac Newton performed a simple experiment that is described in all school textbooks. Having closed the shutters, he made a small hole in them, through which he passed sunbeam. A prism was placed in the path of the beam, and a screen was placed behind the prism.
On the screen, Newton observed a “rainbow”: a white ray of sunlight, passing through a prism, turned into several colored rays - from violet to red. This phenomenon is called light dispersion. Sir Isaac was not the first to observe this phenomenon. Already at the beginning of our era, it was known that large single crystals of natural origin have the property of decomposing light into colors. The first studies of light dispersion in experiments with a glass triangular prism, even before Newton, were carried out by the Englishman Hariot and the Czech naturalist Marzi.
However, before Newton, such observations were not subjected to serious analysis, and the conclusions drawn on their basis were not cross-checked by additional experiments. Both Hariot and Marzi remained followers of Aristotle, who argued that differences in color are determined by differences in the amount of darkness “mixed” with white light. Purple, according to Aristotle, appears with the greatest addition of darkness to light, and red with the least. Newton carried out additional experiments with crossed prisms, when light passed through one prism then passes through another. Based on the totality of his experiments, he concluded that “no color arises from white and black mixed together, except for the intermediate dark ones; the amount of light does not change the appearance of the color.” He showed that white light should be considered as a compound. The main colors are from purple to red. This Newton experiment provides a remarkable example of how different people, observing the same phenomenon, interpret it in different ways, and only those who question their interpretation and carry out additional experiments come to the correct conclusions.
7. Thomas Young's experiment
Until the beginning of the 19th century, ideas about the corpuscular nature of light prevailed. Light was considered to consist of individual particles - corpuscles. Although the phenomena of diffraction and interference of light were observed by Newton (“Newton’s rings”), the generally accepted point of view remained corpuscular. Looking at the waves on the surface of the water from two thrown stones, you can see how, overlapping each other, the waves can interfere, that is, cancel out or mutually reinforce each other. Based on this, English physicist and the physician Thomas Young carried out experiments in 1801 with a beam of light that passed through two holes in an opaque screen, thus forming two independent sources of light, analogous to two stones thrown into water. As a result, he observed an interference pattern consisting of alternating dark and white fringes, which could not be formed if light consisted of corpuscles. The dark stripes corresponded to areas where light waves from the two slits cancel each other out. Light stripes appeared where light waves mutually reinforced each other. Thus, the wave nature of light was proven.
8. Klaus Jonsson's experiment
German physicist Klaus Jonsson conducted an experiment in 1961 similar to Thomas Young's experiment on the interference of light. The difference was that instead of rays of light, Jonsson used beams of electrons. He obtained an interference pattern similar to what Young observed for light waves. This confirmed the correctness of the provisions of quantum mechanics about the mixed corpuscular-wave nature of elementary particles.
9. Robert Millikan's experiment
The idea that the electric charge of any body is discrete (that is, it consists of a larger or smaller set of elementary charges that are no longer subject to fragmentation) arose back in early XIX century and was supported by such famous physicists as M. Faraday and G. Helmholtz. The term “electron” was introduced into the theory, denoting a certain particle - the carrier of an elementary electric charge. This term, however, was purely formal at that time, since neither the particle itself nor the elementary electric charge associated with it had been discovered experimentally.
In 1895, K. Roentgen, during experiments with a discharge tube, discovered that its anode, under the influence of rays flying from the cathode, was capable of emitting its own X-rays, or Roentgen rays. In the same year, French physicist J. Perrin experimentally proved that cathode rays are a stream of negatively charged particles. But, despite the colossal experimental material, the electron remained a hypothetical particle, since there was not a single experiment in which individual electrons would participate. American physicist Robert Millikan developed a method that has become a classic example of an elegant physics experiment.
Millikan managed to isolate several charged droplets of water in space between the plates of a capacitor. By illuminating with X-rays, it was possible to slightly ionize the air between the plates and change the charge of the droplets. When the field between the plates was turned on, the droplet slowly moved upward under the influence of electrical attraction. When the field was turned off, it fell under the influence of gravity. By turning the field on and off, it was possible to study each of the droplets suspended between the plates for 45 seconds, after which they evaporated. By 1909, it was possible to determine that the charge of any droplet was always an integer multiple of the fundamental value e (electron charge). This was convincing evidence that electrons were particles with the same charge and mass. By replacing water droplets with oil droplets, Millikan was able to increase the duration of observations to 4.5 hours and in 1913, eliminating one after another possible sources of error, he published the first measured value of the electron charge: e = (4.774 ± 0.009) x 10-10 electrostatic units.
10. Ernst Rutherford's experiment
By the beginning of the 20th century, it became clear that atoms consist of negatively charged electrons and some kind of positive charge, due to which the atom remains generally neutral. However, there were too many assumptions about what this “positive-negative” system looks like, while there was clearly a lack of experimental data that would make it possible to make a choice in favor of one or another model.
Most physicists accepted J.J. Thomson's model: an atom as a uniformly charged positive ball with a diameter of approximately 10-8 cm with negative electrons floating inside. In 1909, Ernst Rutherford (assisted by Hans Geiger and Ernst Marsden) conducted an experiment to understand the actual structure of the atom. In this experiment, heavy positively charged alpha particles moving at a speed of 20 km/s passed through thin gold foil and were scattered on gold atoms, deviating from the original direction of motion. To determine the degree of deviation, Geiger and Marsden had to use a microscope to observe the flashes on the scintillator plate that occurred where the alpha particle hit the plate. Over the course of two years, about a million flares were counted and it was proven that approximately one particle in 8000, as a result of scattering, changes its direction of motion by more than 90° (that is, turns back). This could not possibly happen in Thomson’s “loose” atom. The results clearly supported the so-called planetary model of the atom - a massive tiny nucleus measuring about 10-13 cm and electrons rotating around this nucleus at a distance of about 10-8 cm.
