slide 2

The first ideas about light

The first ideas about what light is also belong to antiquity. In ancient times, ideas about the nature of light were very primitive, fantastic and, moreover, very diverse. However, despite the diversity of the views of the ancients on the nature of light, already at that time there were three main approaches to solving the problem of the nature of light. These three approaches subsequently took shape in two competing theories - corpuscular and wave theories of light. The overwhelming majority of ancient philosophers and scientists considered light as some kind of rays connecting the luminous body and the human eye. At the same time, three main views on the nature of light were distinguished. Eye->item Item->eye Movement

slide 3

First theory

Some of the ancient scientists believed that the rays come from the eyes of a person, they seem to feel the object in question. This point of view had at first a large number of followers. Such prominent scientists and philosophers as Euclid, Ptolemy and many others adhered to it. However, later, already in the Middle Ages, such an idea of ​​the nature of light loses its meaning. Fewer and fewer scientists follow these views. And by the beginning of the XVII century. this point of view can be considered already forgotten. Euclid Ptolemy

slide 4

Second theory

Other philosophers, on the contrary, believed that the rays are emitted by a luminous body and, reaching the human eye, bear the imprint of a luminous object. This point of view was held by the atomists Democritus, Epicurus, Lucretius. This point of view on the nature of light later, in the 17th century, took shape in the corpuscular theory of light, according to which light is a stream of some particles emitted by a luminous body. Democritus Epicurus Lucretius

slide 5

Third theory

The third point of view on the nature of light was expressed by Aristotle. He considered light not as an outflow of something from a luminous object into the eye, and even more so not as some kind of rays emanating from the eye and feeling the object, but as an action or movement propagating in space (in the environment). Few people shared the opinion of Aristotle in his time. But later, again in the 17th century, his point of view was developed and laid the foundation for the wave theory of light. Aristotle

slide 6

Middle Ages

The most interesting work on optics that has come down to us from the Middle Ages is the work of the Arab scientist Alhazen. He studied the reflection of light from mirrors, the phenomenon of refraction and the passage of light through lenses. The scientist adhered to the theory of Democritus and for the first time expressed the idea that light has a finite propagation speed. This hypothesis was a major step in understanding the nature of light. Alhazen

Slide 7

17th century

On the basis of numerous experimental facts in the middle of the 17th century, two hypotheses about the nature of light phenomena arose: Newton's corpuscular theory, which assumed that light is a stream of particles ejected at high speed by luminous bodies. The wave theory of Huygens, which stated that light is a longitudinal oscillatory motion of a special luminiferous medium (ether), excited by vibrations of particles of a luminous body.

Slide 8

The main provisions of the corpuscular theory

Light consists of small particles of matter emitted in all directions in straight lines, or rays, luminous by a body, such as a burning candle. If these rays, consisting of corpuscles, enter our eye, then we see their source. Light corpuscles have different sizes. The largest particles, getting into the eye, give a sensation of red color, the smallest - purple. White color is a mixture of all colors: red, orange, yellow, green, blue, indigo, violet. The reflection of light from the surface occurs due to the reflection of corpuscles from the wall according to the law of absolute elastic impact.

Slide 9

The phenomenon of light refraction is explained by the fact that corpuscles are attracted by the particles of the medium. The denser the medium, the smaller the angle of refraction is than the angle of incidence. The phenomenon of light dispersion, discovered by Newton in 1666, he explained as follows. “Every color is already present in white light. All colors are transmitted through interplanetary space and the atmosphere together and give the effect of white light. White light - a mixture of various corpuscles - is refracted when passing through a prism. Newton outlined ways to explain double refraction by hypothesizing that light rays have "different sides" - a special property that causes their different refraction when passing through a birefringent body.

Slide 10

Newton's corpuscular theory satisfactorily explained many optical phenomena known at that time. Its author enjoyed tremendous prestige in the scientific world, and soon Newton's theory gained many supporters in all countries. The largest scientists adhering to this theory: Arago, Poisson, Biot, Gay-Lussac. On the basis of the corpuscular theory, it was difficult to explain why light beams, crossing in space, do not act on each other in any way. After all, light particles must collide and scatter (waves pass through each other without mutual influence) Newton Arago Gay-Lussac

slide 11

The main provisions of the wave theory

Light is the distribution of elastic periodic impulses in the ether. These pulses are longitudinal and are similar to sound pulses in air. Ether is a hypothetical medium that fills the celestial space and the gaps between the particles of bodies. It is weightless, does not obey the law of universal gravitation, and has great elasticity. The principle of propagation of ether oscillations is such that each of its points, to which excitation reaches, is the center of secondary waves. These waves are weak, and the effect is observed only where their envelope surface passes - the wave front (Huygens' principle). The farther the wavefront is from the source, the flatter it becomes. Light waves coming directly from the source cause the sensation of seeing. A very important point in Huygens' theory was the assumption that the speed of light propagation is finite.

slide 12

wave theory

With the help of the theory, many phenomena of geometric optics are explained: – the phenomenon of light reflection and its laws; - the phenomenon of light refraction and its laws; – the phenomenon of total internal reflection; - the phenomenon of double refraction; - the principle of independence of light rays. Huygens' theory gave the following expression for the refractive index of the medium: From the formula it can be seen that the speed of light should depend inversely on the absolute index of the medium. This conclusion was the opposite of the conclusion that follows from Newton's theory.

slide 13

Many doubted Huygens' wave theory, but among the few supporters of wave views on the nature of light were M. Lomonosov and L. Euler. From the research of these scientists, Huygens' theory began to take shape as a theory of waves, and not just aperiodic oscillations propagating in the ether. It was difficult to explain the rectilinear propagation of light, leading to the formation of sharp shadows behind objects (according to the corpuscular theory, the rectilinear movement of light is a consequence of the law of inertia) only from the point of view of wave theory. Huygens Lomonosov Euler

Slide 14

XI-XX centuries

In the second half of the 19th century, Maxwell showed that light is a special case of electromagnetic waves. Maxwell's work laid the foundations for the electromagnetic theory of light. After the experimental discovery of electromagnetic waves by Hertz, there was no doubt that light behaves like a wave during propagation. There are none even now. However, at the beginning of the 20th century, ideas about the nature of light began to change radically. It suddenly turned out that the rejected corpuscular theory is still relevant to reality. It turned out that during emission and absorption, light behaves like a stream of particles. Maxwell Hertz

slide 15

Discontinuous (quantum) properties of light have been discovered. An unusual situation arose: the phenomena of interference and diffraction could still be explained by considering light as a wave, and the phenomena of radiation and absorption, by considering light as a stream of particles. Therefore, scientists agreed on the opinion about the corpuscular-wave dualism (duality) of the properties of light. Today, the theory of light continues to develop.

View all slides

Topic:

• Development of views on the nature of light. The speed of light.

• (Physics. Grade 11)

• Completed by: physics teacher

• MOU "Secondary School No. 6"

• Kirov, Kaluga region

• Kochergina V.E.

• 2010

At the end of the 17th century, two seemingly mutually exclusive theories of light arose almost simultaneously.

• They relied on two possible ways of transmitting an action from a source to a receiver.

• I. Newton proposed a corpuscular theory of light, according to which light is a stream of particles coming from a source in all directions (substance transfer).

• H. Huygens developed a wave theory in which light was considered as waves propagating in a special medium - ether, which fills all space and penetrates into all bodies (changing the state of the medium).

Newton Huygens

What is light?

• According to the ideas of modern physics, light simultaneously has the properties of continuous electromagnetic waves and the properties of discrete particles, which are called photons or light quanta.

• The duality of the properties of light is called corpuscular-wave dualism.

Two great confrontations in science. Stages of development of ideas about the nature of light.

This was the first known attempt to experimentally determine the speed of light by Galileo Galilei. However, it was not possible to detect the signal delay due to the high speed of light.

• The first experimental determination of the speed of light was made by the Danish astronomer Olaf Römer in 1675.

• By dividing the diameter of the earth's orbit by the delay time, the value of the speed of light was obtained:

• c \u003d 3 * 1011m / 1320s

• s=2.27*108m/s

• The result obtained had a large error.

The first laboratory measurement of the speed of light was made in 1849 by the French physicist Armand Fizeau.

• In his experiment, the light from the source S passed through the interrupter K (the teeth of a rotating wheel) and, reflected from the mirror Z, returned again to the gear wheel.

Fizeau method:

Fizeau's setup options are as follows. The source of light and the mirror were located in the house of Fizeau's father near Paris, and the mirror - in Montmartre. The distance between the mirrors was ℓ ~ 8.66 km, the wheel had 720 teeth. It rotated under the action of a clockwork set in motion by a descending weight. Using a rev counter and a chronometer, Fizeau found that the first blackout occurs at a wheel speed of v = 12.6 rpm. Light travel time t=2 ℓ/c, therefore gives With = 3,14 10 8 m/s

Despite the significant measurement error, Fizeau's experiment was of great importance - the possibility of determining the speed of light by "terrestrial" means was proved.

• The American physicist A. Michelson developed a perfect method for measuring the speed of light using rotating mirrors.

Michelson method:

In accordance with direct measurement methods, the speed of light in vacuum is now taken equal to

• With =299792458+1.2 m/s

The finiteness of the speed of light is proved experimentally by direct and indirect methods.

• At present, with the help of laser technology, the speed of light is determined by measuring the wavelength and frequency of radio emission by methods independent of each other and is calculated by the formula :

"How many speeds does light have?"

• Until the indications for change With over time, no, but physics cannot unconditionally reject such a possibility. Well, it remains to wait

• messages about new measurements of the speed of light. These measurements can give a lot more to the knowledge of nature, inexhaustible in its diversity.

The purpose of the lesson: to form students' ideas about the nature of light; corpuscular or wave; as determined and then measured the speed of light.

During the classes

1. Analysis of control work.

2. Learning new material

Newton's corpuscular theory. Wave theory of Huygens.

1. Light propagates in the form of a stream 1. Light propagates in ether

Particles (corpuscles) - 17th century. like a stream of waves - 17th century.

Evidence: Straightforward Evidence: Independence

The propagation of light, the formation of beams of light at the intersection.

Shadows. In 1802, Jung obtained the diffraction of light,

In the 19th century, the discovery of the photoelectric effect and in 1803_ - the interference of light,

Proved that light is a stream of particles. proving that light is waves.

These particles are called quanta. Maxwell proved that light is

Electromagnetic waves.

Modern ideas about the nature of light: light has a corpuscular-wave dualism - it is emitted and absorbed in portions, and propagates in the form of waves.

The speed of light.

1. An astronomical method for measuring the speed of light.

The Danish astronomer O. Römer, observing the eclipses of the satellite Io, closest to the planet Jupiter, noticed the delay in its appearance from the shadow of the planet. From this delay of 22 minutes, he was able to calculate the speed of light.

Roemer's calculations were approximate, but most importantly, he proved that light does not propagate instantly, but has a finite speed.

2. Laboratory methods for measuring the speed of light.

In 1849, I. Fizeau (French) was able to measure the speed of light using a laboratory method.

Light from the source falls on a translucent plate, and from it on a rapidly rotating gear wheel. Passing through the slit, between the teeth, the light fell on a mirror located at a distance of 8.6 km. Reflected from the mirror, the light again fell into the slot between the teeth.

Knowing the travel time of the tooth, it was equal to the passage of light to the mirror and back, Fizeau calculated the speed of light. According to his calculations, it was equal to 313,000 km / s.

Many other more accurate laboratory methods have been developed to measure the speed of light. This is the installation of the French physicist Foucault, the American scientist Michelson and the installations of other scientists.

According to modern measurements, the speed of light in vacuum is 299792458 m/s QUOTE .

The speed of light in any media is less than in vacuum. For example, in water it is 3/4 of the speed in a vacuum.

The measurement of the speed of light was of great importance for the development and study of optical phenomena. It turned out that no body or particle can move faster than light.

Consolidation of the studied material

1. What two theories about the nature of light appeared in the 17th century?

31. Development of views on the nature of light. The speed of light. Huygens principle. The law of reflection of light. (Aslapovskaya S.V.)

Lesson text

• Abstract

  Subject name: Physics Grade: 11 TMC: Physics Grade 11, G. Ya. Myakishev, B. B. Bukhovtsev, 2010. Level of education: basic Theme of the lesson: "Development of views on the nature of light. Speed ​​of light. Huygens principle. Law of reflection of light." The total number of hours allotted for the study of the topic: 19 Place of the lesson in the system of lessons on the topic: the first lesson of the study of the topic "Optics". The purpose of the lesson: providing perception and understanding of the essence of the nature of light. Lesson objectives: To learn about the contribution that scientists from different countries have made to the development of ideas about the nature of light. Draw conclusions about the nature of light based on the information received. Create a reference abstract "Development of views on the nature of light." Expected results: students should realize how difficult the path of human cognition of natural phenomena is, repeat the laws of light reflection, get an idea of ​​the Huygens principle. Technical support of the lesson: multimedia projector, presentation for the lesson, handouts. Additional methodological and didactic support for the lesson (links to Internet resources are possible): the date and topic of the lesson are written on the blackboard, the tables are arranged for work in groups (2 students each). Preparation for the lesson: groups are formed, working material is on the tables (an archive with the necessary literature, documents and a task that the DO must complete). The teacher explains the goals and objectives of the lesson. During the allotted time, the groups prepare the task. Lesson content. I. Introductory part of the lesson 1. Organizational stage (1 min). The class is divided into 5 groups pre-formed by the teacher (scientific societies (NS)), each of which has a head of the NO, a literary fellow, and a researcher. Groups receive a task and the sources of information necessary for its implementation. 2. Actualization of mental activity (2 min). Teacher. Good afternoon everyone, sit down! How beautiful is this world filled with light! What is light for you? What associations does the word light evoke in you? (presentation slides from No. 1-8 with musical accompaniment are scrolled on the screen (by clicking the hyperlink)). Teacher. Light is a radiant energy perceived by the eye that makes the world visible. Light entered our home. How was it born and originated? There is a secret in his nature, And there has been a dispute for many years. 3. Purpose and objectives of the lesson (2 min). On the screen, slide No. 9-12 Tasks: Learn about the contribution that scientists from different countries have made to the development of ideas about the nature of light (to solve this problem, we will go on a virtual scientific trip). Draw conclusions about the nature of light on the basis of the information received (you will solve this problem by speaking in the program "Obvious and Incredible" with the results of your scientific trip). Create a reference abstract "Development of views on the nature of light." Each of you has an OK matrix on the table, which you must complete (you will solve this problem throughout the lesson). I have already said that today we will not just work, but will work according to the plan-task of the "Obvious and Incredible" program. I suggest you go on a virtual scientific trip to different countries and different eras in order to work in archives, study literature, documents and establish what scientists from different countries have done in order to find out the nature of light. You must also prepare and present the results of your work. 5 scientific societies (NO) go on a business trip to the following countries: Denmark, France, England, Holland (on the screen, slide No. 13: a map of the World with these countries, by clicking the named country is marked on the map). Each scientific society has on its tables an archive with the necessary literature, documents and a task that the DO must complete. The trip takes 10 minutes. During this time, music will sound, and as soon as it ends, you must perform on the program with the results of your work. So, I ask you to start the task (music sounds after clicking on the "call" hyperlink on slide No. 13). II. The main part of the lesson. 1. Independent work of students in groups (10 min, preparing students for performances NO): First NO: Country: Denmark, scientist: Olaf Römer, 1676 - an astronomical method for measuring the speed of light. Head of the NO (informs where they have been) Literary staff (select material about the scientist) Research workers (preparing a report on the method of measuring the speed of light (the theory of the nature of light)) Examples of answers NO: 1 student. Our BUT visited Denmark. We worked at the Academy of Sciences in the department where documents are collected about Olaf Römer (1644-1710), who measured the speed of light by astronomical method (slide No. 14 on the screen). 2 student. Römer Olaf Christensen (1644-1710), Danish physicist and astronomer. In 1676 he made an important discovery: he proved the finiteness of the speed of light and measured its magnitude. However, the scientist's message at a meeting of the Paris Academy of Sciences was sharply criticized. Despite criticism, his conclusions were accepted by H. Huygens, Leibniz, I. Newton. The final validity of Roemer's theory was confirmed in 1725. after the discovery by astronomer Bradley of the phenomenon of aberration of light. Returning to Denmark in 1681, he headed the department of mathematics at the University of Copenhagen and created an observatory. He also took part in the political and social life of Denmark. At the end of his life he became the head of the State Council. Invented new astronomical instruments. Römer's name is entered on the map of the Moon (on the screen, slide No. 15). 3 student. In 1676, while observing the eclipse of Jupiter's moon Io, Römer discovered. That when the earth in six months passes to the other side of the Sun, more distant from Jupiter, then Io appears 22 minutes later than the calculated time. This delay was explained by the increase in the distance from Jupiter to the Earth. Knowing the size of the earth's orbit and the delay time, Roemer calculated the speed of light propagation (on the screen, slide No. 15: by clicking on the hyperlink "method diagram", slide No. 16 - laboratory method diagram in full screen). C = 300,000 km / s (after the additions of the teacher, a conclusion appears on slide No. 15 by clicking on it) Second NO: Country: France, scientist: Fizeau Armand Hippolyte Louis, 1849 - laboratory method for measuring the speed of light 1 student. Our BUT visited France. We worked at the Paris Academy of Sciences, in the department where documents are collected about Armand Fizeau, who measured the speed of light propagation using a laboratory method (slide No. 17 on the screen). 2 student. Fizeau (1819-1896) - French physicist. In 1863 he became a professor at the Polytechnic School in Paris. Fizeau's first major achievement in optics was his experiments on the interference of light. In 1849 he staged a classical experiment to determine the speed of light. He designed a number of devices: an induction coil. Interference spectroscope; explored crystals while taking photographs. In 1875 he was elected a member of the Royal Society of London, in 1866 he was awarded the Rumfoord medal (slide No. 18 on the screen). 3 student. According to the scheme: for the first time, I. Fizeau managed to measure the speed of light by a laboratory method in 1849. Experiment: light from a source, passing through a lens, fell on a translucent plate. After reflection from the plate, the focused narrow beam was directed to a rapidly rotating gear wheel. Passing between the teeth, the light reached a mirror located at a distance of several kilometers from the wheel. Reflected from the mirror, the light returned again to the cogwheel and had to pass again between the teeth. When the wheel turned slowly, the light reflected from the mirror was visible. As the speed increased, it gradually disappeared. Why? While the light went to the mirror and back, the wheel had time to turn so that a tooth stood in place of the slot, and the light ceased to be visible. With a further increase in the speed of rotation of the wheel, the light again became visible. During this time of propagation of light to the mirror and back, the wheel had time to turn so that a new slot would rise in place of the previous slot. Knowing this time and the distance between the wheel and the mirror, you can determine the speed of light (c = 313 km/s) (after the student's message, by clicking on slide No. 18, a demonstration of the experiment from the collection "Cyril and Methodius" is shown on the screen (slide No. 19)). (After the teacher's additions, a conclusion appears on slide No. 20 by clicking on it) Third BUT: Country: England, scientist: Isaac Newton, theory of the nature of light 1 student. Our BUT visited England. We worked at the English Academy of Sciences in the department where documents about I. Newton are collected: (on the screen, slide No. 22) 2 student. Newton Isaac (1643-1727) - English mathematician, mechanic, astronomer and physicist, creator of classical mechanics. Member (1672) and President (1703) of the Royal Society of London. Fundamental works "Mathematical Principles of Natural Philosophy" (1687) and "Optics" (1704). He discovered the dispersion of light, studied interference and diffraction. Developed the corpuscular theory of light. Built a mirror telescope. Formulated the basic laws of classical mechanics. He discovered the law of universal gravitation, gave the theory of the motion of celestial bodies. He created the basics of celestial mechanics (on the screen, slide No. 23). 3 student. Newton was a supporter of the corpuscular theory of light - light is a stream of particles-corpuscles coming from a source in all directions. This theory easily explained the rectilinear propagation, reflection and refraction of light. The outstanding scientist Newton had great authority among his colleagues, and therefore most of them supported the corpuscular theory, believing that light propagates as a stream of particles, not a wave (on the screen, slide No. 23 - a conclusion appears on a click, a picture on a second click). Fourth BUT: Country: Holland, scientist: Christian Huygens, theory of the nature of light 1 student. We visited Holland: (on the screen slide No. 24) 2 student. H. Huygens (1629-1695) - Dutch mathematician, physicist, astronomer. Invented a pendulum clock with a trigger, established the laws of oscillation of a physical pendulum. Created and published the wave theory of light. He improved the telescope, designed an eyepiece, discovered the ring of Saturn and its satellite Titan. He was elected a member of the Royal Society of London. Part of his work: the results of a study on elastic impact and centrifugal force were published after his death (slide No. 25 on the screen). 3 student. H. Huygens opposed the corpuscular theory of light. Huygens' wave theory of light explained such optical phenomena as interference and diffraction, which the corpuscular theory could not explain. According to the Huygens wave theory, light is a wave propagating in a special hypothetical (elastic) medium-ether, which fills all space and all bodies (slide No. 25 on the screen - a conclusion appears on a click, a picture appears on a second click). Fifth NO: Country: England, scientist: Thomas Jung, development of the wave theory of light Country: France, scientist: Augustin Jean Fresnel, development of the wave nature of light 1 student. We visited England and visited France (on the screen slide No. 26) 2 student. Young Thomas (1773-1829) English physicist. At the age of 21 (1794) he became a member of the Royal Society. Received a doctorate in medicine. Opened a private practice in London. Jung's research in the field of optics formed the basis of his article "The Mechanism of the Eye" (1800), in which he explained the nature of accommodation, astigmatism and color vision. He was appointed professor at the Royal Institute. One of the founders of the wave theory of light. In 1803 he explained the phenomenon of light interference. He put forward a hypothesis about the transverseness of light vibrations. Measured the wavelengths of light of different colors. In the theory of elasticity, Young belongs to the study of shear deformation (on the screen, slide No. 27 - a photograph appears at the first click). 3 student. T. Jung first introduced the concept of "interference". Jung discovered interference by observing this phenomenon for water waves. Jung presented the results of his research in optics at a scientific meeting of the Royal Society of London, and also published them at the beginning of the 19th century. But, despite the persuasiveness of Jung's works, no one wanted to recognize them. it meant abandoning conventional wisdom and, moreover, opposing Newton's authority. Jung's work went unnoticed, and even an article appeared in the press containing rude attacks on him. 4 student. Fresnel Augustin Jean (1788-1827), French physicist, one of the creators of the wave theory of light. Fresnel's works are devoted to physical optics. He began to study physics on his own and soon began to conduct experiments in optics. In 1815, he rediscovered the principle of interference, adding several new ones to T. Jung's experiments. In 1821 he proved the transverseness of light waves, in 1823 he established the laws of light polarization. Invented a number of interference devices. In 1823 Fresnel was elected a member of the Paris Academy of Sciences. In 1825 he became a member of the Royal Society of London. The French engineer, who later became a famous physicist O. Fresnel, began to study the phenomena of interference and diffraction from 1814. He did not know about Jung's work, but like him he saw in these phenomena proof of the wave theory of light. However, gradually, despite all the difficulties faced by the hypothesis of the transverseness of light waves, the wave theory, light began to win and displace the corpuscular theory of light (slide No. 27 on the screen - a photograph appears on the second click). (After the teacher's additions, a conclusion appears on slide No. 27 by clicking) 2. Presentation of the results of the work of the NO (15 - 20 min.): Teacher. Now we are starting to present the results of our scientific trip. At the beginning of the lesson, we set ourselves the problem - to find out the nature of light. During presentations, do not forget to fill out the OK template (on the students' desks there are sheets with a template for the reference notes). The first great advance in the study of the nature of light was the measurement of the speed of light. It turned out that the speed of light propagation is not infinitely great. The problem of measuring the speed of light was first formulated by Galileo (XVI century), who raised the question of the finiteness of the speed of light. But he could not answer the question he posed. The speed of light was eventually measured (on screen slide #21). I BUT: (Denmark, Römer) - student performances (presentation slides No. 14-16). Teacher additions. Roemer himself, due to the low accuracy of measurements and inaccurate knowledge of the radius of the Earth's orbit, obtained a value of 215,000 km / s for the speed of light. II NO: (France, Fizeau) - student performances (presentation slides No. 17-20). Teacher additions. More precisely, the speed of light began to be measured after 1960, when the first laser began to work. According to modern data, the speed of light in vacuum is equal to the value that you see on the screen (slide No. 21) with an accuracy of + (-) 0.2 m/s. Approximately c \u003d 3 * 108 m / s (must be remembered). Where did you meet this figure? (This value, obtained experimentally, coincides with the value predicted by Maxwell and experimentally measured for the first time by Hertz - the speed of electromagnetic waves). The value of the speed of light will help determine the nature of light. Since ancient times, man has been interested in the nature of light. There were various legends, myths, hypotheses, scientific works. In the 16th century, man did not yet know the nature of light. In the 17th century, completely different theories began to exist almost simultaneously about what light is, what is its nature ?! III BUT: (England, Newton) - student performances (presentation slides No. 22-23). IV NO: (Holland, Huygens) - student performances (presentation slides No. 24-25). Teacher additions. Conclusion: the first theory stated: light is a stream of particles coming from a source in all directions; the second theory stated: light is a wave propagating in a special hypothetical medium - ether. V NO: (England, T. Jung; France, O. Fresnel) - student performances (presentation slides No. 26-27). Teacher additions. Thus, a turn was made to the wave nature of light. A number of experiments carried out in the 19th century, as well as the works of Maxwell, which were then confirmed in the experiments of Hertz, proved the validity of the wave theory: light propagates as an electromagnetic wave. III. Final part of the lesson Debriefing (5 min): What product did we get? Let's get back to your OK. Please note that you have completed everything. Let's compare your reference notes (MC) with the one presented on the screen (presentation slide #28). But what about Newton's theory? He had a brilliant idea that light can be considered as a particle. Was he right? And he was right, because. in the 20th century, ideas about the nature of light began to change, when the quantum properties of light were discovered, scientists had to recall the corpuscular theory. What is the nature of light? Conclusion: light has a dual nature - corpuscular-wave (presentation slide No. 29, the output appears on the first click, the picture appears on the second click). Light is a stream of particles; light is a wave. "What is not clear should be clarified" (Confucius). You will learn about this later (presentation slides No. 30-37, music sounds after clicking the hyperlink). Homework: pp. 168-170, p. 59, ind. Task p. 60. In preparation, I used the sites: 1. http://nsportal.ru 2. http://festival.1september.ru/articles/614775/ 3. https://videouroki.net/razrabotki/fizika/uroki -1/11-class/3 4. https://infourok.ru/konspekt_otkrytogo_uroka_po_fizike_otrazhenie_sveta_11_klass-565783.htm

Questions about the nature of light and the laws of propagation were raised by Greek philosophers. Euclid (300 BC) explained visual perception by visual rays emanating from the eyes that felt the object. He also formulated the law of rectilinear propagation of light. Optics received rapid development in the late 16th and early 17th centuries, when the Dutch scientist Jansen (1590) built the first two-lens microscope, and Galileo (1609) made a number of astrological discoveries with his telescope (Wiener phases, Jupiter's moons, mountains on the Moon). In 1620, the Dutch scientist Snell finally established the law of refraction, which was written in the usual form for us by the French scientist Descartes.

A great contribution to the development of optics was made by Isaac Newton (late 17th century). Based on the straightness of light, as well as the laws of reflection and refraction, he suggested that light is a stream of corpuscles emitted by a luminous body and flying at great speed according to mechanical laws. He was able to explain the rectilinearity of the propagation of light in a homogeneous medium, corpuscles move by inertia. The law of reflection: corpuscles are reflected from the boundary of 2 media, like balls from a flat surface. Newton also explained the law of refraction, but not by a decrease, but by an increase in the speed of movement of corpuscles in a denser medium. Newton also showed that white light is composite and contains “pure colors”, the corpuscles of which differ in mass: the purple corpuscles are the lightest, and the red corpuscles are the heaviest (not guessed).

Along with Newton's corpuscular concept of light, the Hooke-Huygens wave theory (the propagation of longitudinal deformations in the so-called world ether) arose and developed in the 17th century. Using the Huygens principle, any point to which a light wave has reached is a source of secondary waves, it is also possible to explain the law of reflection and refraction, and the phenomena of diffraction (enveloping obstacles) and interference (superposition).

Thus, by the end of the 17th century, two opposing systems of views on the nature of light (corpuscular and wave) had developed in optics, both of which explained the basic laws of geometric optics, but each had its own shortcomings. Huygens was unable to explain the dispersion of different refractive indices for different colors (Newton could). But Newton, when explaining that light is partially reflected and partially refracted, had to suggest that a corpuscle experiences bouts of reflection and refraction. However, the authority of Newton led to the fact that throughout the 18th century, most physicists were inclined towards the corpuscular theory of light. Neither theory can explain the birefringence discovered in 1724 by Bartalimus, as well as the phenomenon of light correlation. In 1717, Newton showed that the correlation of light could only be explained by transverse waves, which Newton believed disproved the wave theory of light. At the beginning of the 19th century, mathematicians developed the theory of oscillations and waves, which was successfully applied to some optical phenomena. So in 1801, the English scientist Jung established the principle of interference, Fresnel (in 1815) clarified the Huygens principle, adding to it that secondary waves interfere, and this made it possible to explain the interference of light. On the basis of the experiments of Faraday and Argo on the interference of polarized light, Jung proposed that light is a transverse wave, it was necessary to attribute elastic properties to the ether (that is, the ether is not a liquid or gas, but a solid body).

Faraday's experiments in 1846 on interaction with a magnetic field, as well as Maxwell's research in 1845, made it possible to prove that light is an electromagnetic wave. Maxwell's theory made it possible to explain and quantify the propagation speed of electromagnetic waves, and hence of light, in various media. It seemed that the wave theory won, but the results of the study of the spectral features of the radiation of an absolute black body, which appeared by the end of the 19th century. In 1901, Planck showed that the emission and absorption of electromagnetic waves do not occur continuously. Electromagnetic waves are emitted in portions (quanta), and the energy of each portion is determined only by the frequency E = h v. Einstein in 1905 explained the laws of the photoelectric effect by introducing light particles - photons. That is, Einstein showed that light is not only absorbed and emitted by quanta, but also propagates in the form of particles, while remaining a wave. These discoveries by Planck and Einstein led to the emergence of quantum mechanics, which developed throughout the 20th century.