Introduction

1. Literary review

1.1. History of the development of geometric optics

1.2. Basic concepts and laws of geometric optics

1.3. Prism elements and optical materials

2. Experimental part

2.1 Materials and experimental technique

2.2. Experimental results

2.2.1. Demonstration experiments using a glass prism with a refractive angle of 90º

2.2.2. Demonstration experiments using a glass prism filled with water, with a refractive angle of 90º

2.2.3. Demonstration experiments using a hollow glass prism, filled with air, with a refractive angle of 74º

2.3. Discussion of experimental results

List of used literature

Introduction

The decisive role of experiment in the study of physics at school corresponds to the main principle of the natural sciences, according to which experiment is the basis for the knowledge of phenomena. Demonstration experiments contribute to the creation of physical concepts. Among the demonstration experiments, one of the most important places is occupied by experiments in geometric optics, which make it possible to visually show the physical nature of light and demonstrate the basic laws of light propagation.

In this paper, the problem of setting up experiments on geometric optics using a prism in high school is investigated. The most visual and interesting experiments in optics were selected using equipment that can be purchased by any school or made independently.

Literature review

1.1 The history of the development of geometric optics.

Optics refers to such sciences, the initial ideas of which arose in ancient times. Throughout its centuries-old history, it has experienced continuous development, and is currently one of the fundamental physical sciences, enriched by discoveries of new phenomena and laws.

The most important problem in optics is the question of the nature of light. The first ideas about the nature of light arose in ancient times. Ancient thinkers tried to understand the essence of light phenomena, based on visual sensations. The ancient Hindus thought that the eye had a "fiery nature". The Greek philosopher and mathematician Pythagoras (582-500 BC) and his school believed that visual sensations arise due to the fact that “hot vapors” come from the eyes to objects. In their further development, these views took a clearer form in the form of the theory of visual rays, which was developed by Euclid (300 BC). According to this theory, vision is due to the fact that “visual rays” flow from the eyes, which feel the body with their ends and create visual sensations. Euclid is the founder of the doctrine of rectilinear propagation of light. Applying mathematics to the study of light, he established the laws of reflection of light from mirrors. It should be noted that for the construction of a geometric theory of light reflection from mirrors, the nature of the origin of light does not matter, but only the property of its rectilinear propagation is important. The regularities found by Euclid have been preserved in modern geometric optics. Euclid was also familiar with the refraction of light. At a later time, similar views were developed by Ptolemy (70-147 AD). They paid great attention to the study of the phenomena of light refraction; in particular, Ptolemy made many measurements of the angles of incidence and refraction, but he failed to establish the law of refraction. Ptolemy noticed that the position of the stars in the sky changes due to the refraction of light in the atmosphere.

In addition to Euclid, other scientists of antiquity also knew the effect of concave mirrors. Archimedes (287-212 BC) is credited with burning the enemy fleet with a system of concave mirrors, with which he collected the sun's rays and sent them to the Roman ships. A certain step forward was made by Empedocles (492-432 BC), who believed that outflows from luminous bodies are directed towards the eyes, and outflows come from the eyes towards the bodies. When these outflows meet, visual sensations arise. The famous Greek philosopher, the founder of atomism, Democritus (460-370 BC, e.) completely rejects the idea of ​​visual rays. According to the views of Democritus, vision is due to the fall on the surface of the eye of small atoms emanating from objects. Similar views were later held by Epicurus (341-270 BC). The famous Greek philosopher Aristotle (384-322 BC), who believed that the cause of visual sensations lies outside the human eye, was also a decisive opponent of the "theory of visual rays". Aristotle made an attempt to explain colors as the result of a mixture of light and darkness.

It should be noted that the views of ancient thinkers were mainly based on the simplest observations of natural phenomena. Ancient physics did not have the necessary foundation in the form of experimental research. Therefore, the teaching of the ancients about the nature of light is speculative. Nevertheless, although these views are for the most part only brilliant conjectures, they certainly had a great influence on the further development of optics.

The Arab physicist Alhazen (1038) developed a number of problems in optics in his research. He was engaged in the study of the eye, the refraction of light, the reflection of light in concave mirrors. When studying the refraction of light, Algazei, in contrast to Ptolemy, proved that the angles of incidence and refraction are not proportional, which was the impetus for further research in order to find the law of refraction. Alhazen knows the magnifying power of spherical glass segments. On the question of the nature of light, Alhazen is on the right positions, rejecting the theory of visual rays. Alhazen proceeds from the idea that rays emanate from each point of a luminous object, which, reaching the eye, cause visual sensations. Alhazen believed that light has a finite propagation velocity, which in itself represents a major step in understanding the nature of light. Alhazen gave the correct explanation for the fact that the Sun and Moon seem to be larger on the horizon than at the zenith; he explained it as a delusion of the senses.

Renaissance. In the field of science, the experimental method of studying nature is gradually winning. During this period, a number of outstanding inventions and discoveries were made in optics. Francis Mavrolik (1494-1575) is credited with a fairly accurate explanation of the action of glasses. Mavrolik also found that concave lenses do not collect, but scatter rays. He found that the lens is the most important part of the eye, and concluded that the causes of farsightedness and myopia as a consequence of the abnormal refraction of light by the lens of Mavrolik gave a correct explanation for the formation of images of the Sun, observed when the sun's rays pass through small holes. Next, we should name the Italian Port (1538-1615), who in 1589 invented the camera obscura - the prototype of the future camera. A few years later, the main optical instruments, the microscope and the telescope, were invented.

The invention of the microscope (1590) is associated with the name of the Dutch master optician Zachary Jansen. Spotting scopes began to be made at about the same time (1608-1610) by the Dutch opticians Zachary Jansen, Jacob Metzius and Hans Lippershey. The invention of these optical instruments led in the following years to major discoveries in astronomy and biology. The German physicist and astronomer N. Kepler (1571-1630) owns fundamental works on the theory of optical instruments and physiological optics, the founder of which he can rightly be called, Kepler worked a lot on the study of light refraction.

Fermat's principle, named after the French scientist Pierre Fermat (1601-1665), who formulated it, was of great importance for geometric optics. This principle established that light between two points propagates along such a path, the passage of which takes a minimum of time. It follows that Fermat, in contrast to Descartes, considered the speed of light to be finite. The famous Italian physicist Galileo (1564-1642) did not conduct systematic work on the study of light phenomena. However, in optics he owns works that have brought remarkable results to science. Galileo improved the telescope and first applied it to astronomy, in which he made outstanding discoveries that contributed to the justification of the latest views on the structure of the Universe, based on the heliocentric system of Copernicus. Galileo managed to create a telescope with a frame magnification of 30, which was many times greater than the magnification of the telescopes of its first inventors. With its help, he discovered mountains and craters on the surface of the Moon, discovered satellites near the planet Jupiter, discovered the stellar structure of the Milky Way, etc. Galileo tried to measure the speed of light under terrestrial conditions, but did not succeed due to the weakness of the experimental means available for this purpose. . It follows that Galileo already had correct ideas about the finite speed of light propagation. Galileo also observed sunspots. The priority of the discovery of sunspots by Galileo was disputed by the Jesuit scientist Pater Scheiner (1575-1650), who made accurate observations of sunspots and solar flares using a telescope arranged according to the Kepler scheme. The remarkable thing about Scheiner's work is that he turned the telescope into a projection device, extending the eyepiece more than was necessary for clear vision of the eye, this made it possible to obtain an image of the Sun on the screen and demonstrate it at various degrees of magnification to several persons at the same time.

The 17th century is characterized by further progress in various fields of science, technology and production. Mathematics is developing significantly. Scientific societies and academies uniting scientists are being created in various European countries. Thanks to this, science becomes the property of a wider circle, which contributes to the establishment of international relations in science. In the second half of the 17th century, the experimental method of studying natural phenomena finally won.

The largest discoveries of this period are associated with the name of the brilliant English physicist and mathematician Isaac Newton / (1643-1727). Newton's most important experimental discovery in optics is the dispersion of light in a prism (1666). Investigating the passage of a beam of white light through a trihedral prism, Newton found that a beam of white light breaks up into an infinite set of colored rays that form a continuous spectrum. From these experiments, it was concluded that white light is a complex radiation. Newton also performed the reverse experiment, collecting with the help of a lens the colored rays formed after passing a beam of white light through a prism. As a result, he again received white light. Finally, Newton experimented with mixing colors using a rotating circle, divided into several sectors, painted in the primary colors of the spectrum. When the disc was rotated rapidly, all colors merged into one, giving the impression of white.

Newton laid the results of these fundamental experiments at the basis of the theory of colors, which had not been successful before for any of his predecessors. According to the theory of colors, the color of a body is determined by those rays of the spectrum that this body reflects; the body absorbs other rays.

1.2 Basic concepts and laws of geometric optics. The branch of optics that is based on the concept of light rays as straight lines along which light energy propagates is called geometric optics. This name was given to it because all the phenomena of the propagation of light here can be investigated by geometric constructions of the path of rays, taking into account the law of reflection and refraction of light. This law is the basis of geometric optics.

However, where we are talking about phenomena, the interaction of light with obstacles, the dimensions of which are small enough, the laws of geometric optics are insufficient and it is necessary to use the laws of wave optics. Geometric optics makes it possible to analyze the basic phenomena associated with the passage of light through lenses and other optical systems, as well as with the reflection of light from mirrors. The concept of a light beam as an infinitely thin beam of light propagating in a straight line naturally leads to the laws of rectilinear propagation of light and independent propagation of light beams. It is these laws, together with the laws of refraction and reflection of light, that are the basic laws of geometric optics, which not only explain many physical phenomena, but also allow calculations and design of optical devices. All these laws were initially established as empirical, that is, based on experiments, observations.

Most people, remembering their school years, are sure that physics is a very boring subject. The course includes many tasks and formulas that will not be useful to anyone in later life. On the one hand, these statements are true, but, like any subject, physics has the other side of the coin. But not everyone discovers it for themselves.

A lot depends on the teacher.

Perhaps our education system is to blame for this, or maybe it's all about the teacher, who thinks only about the need to reprimand the material approved from above, and does not seek to interest his students. Most of the time it's his fault. However, if the children are lucky, and the lesson will be taught by a teacher who loves his subject himself, then he will be able not only to interest the students, but also help them discover something new. As a result, it will lead to the fact that children will begin to attend such classes with pleasure. Of course, formulas are an integral part of this academic subject, there is no escape from this. But there are also positive aspects. Experiments are of particular interest to students. Here we will talk about this in more detail. We will look at some fun physics experiments that you can do with your child. It should be interesting not only to him, but also to you. It is likely that with the help of such activities you will instill in your child a genuine interest in learning, and "boring" physics will become his favorite subject. it is not difficult to carry out, this will require very few attributes, the main thing is that there is a desire. And, perhaps, then you can replace your child with a school teacher.

Consider some interesting experiments in physics for the little ones, because you need to start small.

paper fish

To conduct this experiment, we need to cut out a small fish from thick paper (you can use cardboard), the length of which should be 30-50 mm. We make a round hole in the middle with a diameter of about 10-15 mm. Next, from the side of the tail, we cut a narrow channel (width 3-4 mm) to a round hole. Then we pour water into the basin and carefully place our fish there so that one plane lies on the water, and the second remains dry. Now you need to drip oil into the round hole (you can use an oiler from a sewing machine or a bicycle). The oil, trying to spill over the surface of the water, will flow through the cut channel, and the fish, under the action of the oil flowing back, will swim forward.

Elephant and Pug

Let's continue to conduct entertaining experiments in physics with your child. We suggest that you introduce your baby to the concept of a lever and how it helps to facilitate a person’s work. For example, tell us that you can easily lift a heavy wardrobe or sofa with it. And for clarity, show an elementary experiment in physics using a lever. To do this, we need a ruler, a pencil and a couple of small toys, but always of different weights (that's why we called this experiment "Elephant and Pug"). We fasten our Elephant and Pug to different ends of the ruler using plasticine, or an ordinary thread (we just tie the toys). Now, if you put the ruler with the middle part on the pencil, then, of course, the elephant will pull, because it is heavier. But if you shift the pencil towards the elephant, then Pug will easily outweigh it. This is the principle of leverage. The ruler (lever) rests on the pencil - this place is the fulcrum. Next, the child should be told that this principle is used everywhere, it is the basis for the operation of a crane, a swing, and even scissors.

Home experience in physics with inertia

We will need a jar of water and a household net. It will not be a secret for anyone that if you turn an open jar over, the water will pour out of it. Let's try? Of course, for this it is better to go outside. We put the jar in the grid and begin to smoothly swing it, gradually increasing the amplitude, and as a result we make a full turn - one, two, three, and so on. Water does not pour out. Interesting? And now let's make the water pour up. To do this, take a tin can and make a hole in the bottom. We put it in the grid, fill it with water and begin to rotate. A stream shoots out of the hole. When the jar is in the lower position, this does not surprise anyone, but when it flies up, the fountain continues to beat in the same direction, and not a drop from the neck. That's it. All this can explain the principle of inertia. When the bank rotates, it tends to fly straight, but the grid does not let it go and makes it describe circles. Water also tends to fly by inertia, and in the case when we made a hole in the bottom, nothing prevents it from breaking out and moving in a straight line.

Box with a surprise

Now consider experiments in physics with displacement. You need to put a matchbox on the edge of the table and slowly move it. The moment it passes its middle mark, a fall will occur. That is, the mass of the part extended beyond the edge of the tabletop will exceed the weight of the remaining one, and the boxes will tip over. Now let's shift the center of mass, for example, put a metal nut inside (as close to the edge as possible). It remains to place the boxes in such a way that a small part of it remains on the table, and a large one hangs in the air. The fall will not happen. The essence of this experiment is that the entire mass is above the fulcrum. This principle is also used throughout. It is thanks to him that furniture, monuments, transport, and much more are in a stable position. By the way, the children's toy Roly-Vstanka is also built on the principle of shifting the center of mass.

So, let's continue to consider interesting experiments in physics, but let's move on to the next stage - for sixth grade students.

water carousel

We need an empty tin can, a hammer, a nail, a rope. We pierce a hole in the side wall at the very bottom with a nail and a hammer. Next, without pulling the nail out of the hole, bend it to the side. It is necessary that the hole be oblique. We repeat the procedure on the second side of the can - you need to make sure that the holes are opposite each other, but the nails are bent in different directions. We punch two more holes in the upper part of the vessel, we pass the ends of a rope or a thick thread through them. We hang the container and fill it with water. Two oblique fountains will start to beat from the lower holes, and the can will begin to rotate in the opposite direction. Space rockets work on this principle - the flame from the engine nozzles hits in one direction, and the rocket flies in the other.

Experiments in physics - Grade 7

Let's do an experiment with mass density and find out how you can make an egg float. Experiments in physics with different densities are best done on the example of fresh and salt water. Take a jar filled with hot water. We put an egg in it, and it immediately sinks. Next, add salt to the water and stir. The egg begins to float, and the more salt, the higher it will rise. This is because salt water has a higher density than fresh water. So, everyone knows that in the Dead Sea (its water is the most salty) it is almost impossible to drown. As you can see, experiments in physics can significantly increase the horizons of your child.

and a plastic bottle

Schoolchildren of the seventh grade begin to study atmospheric pressure and its effect on the objects around us. To reveal this topic more deeply, it is better to conduct appropriate experiments in physics. Atmospheric pressure affects us, although it remains invisible. Let's take an example with a balloon. Each of us can inflate it. Then we will put it in a plastic bottle, put the edges on the neck and fix it. Thus, air can only enter the ball, and the bottle becomes a sealed vessel. Now let's try to inflate the balloon. We will not succeed, since the atmospheric pressure in the bottle will not allow us to do this. When we blow, the balloon begins to displace the air in the vessel. And since our bottle is airtight, it has nowhere to go, and it begins to shrink, thereby becoming much denser than the air in the ball. Accordingly, the system is leveled, and it is impossible to inflate the balloon. Now we will make a hole in the bottom and try to inflate the balloon. In this case, there is no resistance, the displaced air leaves the bottle - atmospheric pressure equalizes.

Conclusion

As you can see, experiments in physics are not at all complicated and quite interesting. Try to interest your child - and studying for him will be completely different, he will begin to attend classes with pleasure, which will eventually affect his academic performance.

How to put a flat mirror on a drawn rectangle to get an image: triangle, quadrangle, pentagon. Equipment: a flat mirror, a sheet of paper with a square drawn on it. Answer

FRAGMENT OF THE FILM

Watson, I have a small task for you, - shaking the hand of a friend, Sherlock Holmes said quickly. - Remember the murder of the jeweler, the police claim that the driver of the car was driving at a very low speed, and the jeweler himself threw himself under the wheels of the car, so the driver did not have time to slow down. But it seems to me that everything was wrong, the car was driving at high speed and the murder on purpose. It is difficult to determine the truth now, but it became known to me that this episode was accidentally caught on film, as a film was being shot at that time. So I ask you, Watson, get this episode, just a few meters of film.

But what will it give you? - asked Watson.

I don't know yet, was the reply.

Some time later, friends were sitting in the cinema hall and, at the request of Sherlock Holmes, they were watching a small episode.

The car had already driven some distance, the jeweler lay almost motionless on the road. A cyclist on a sports racing bike passes by the lying jeweler.

Notice, Watson, that the cyclist has the same speed as the car. The distance between the cyclist and the car does not change throughout the episode.

And what follows from this? Watson wondered.

Wait a minute, let's watch the episode again, - Holmes whispered imperturbably.

The episode was repeated. Sherlock Holmes was thoughtful.

Watson, did you notice the cyclist? the detective asked again.

Yes, they had the same speed, - Dr. Watson confirmed.

Have you noticed the wheels of a cyclist? Holmes asked.

Wheels, like wheels, consist of three spokes arranged at an angle of 120 ° - an ordinary racing bicycle, the doctor reasoned.

But, how did you count the number of spokes? the famous detective asked.

Very simply, while watching the episode, I got the impression that ... the cyclist is standing still, since the wheels are not rotating.

But the cyclist was moving, - said Sherlock Holmes.

Moved, but the wheels did not rotate, - confirmed Watson.

Russian light

In 1876 in London at the exhibition of precise physical devicesditch Russian inventor Pavel Nikolaevich Ya blochkov demonstrated to visitors an extraordinary electric candle. Similar in shape to ordinary stearic, uh that candle burned with a blindingly bright light. In the same year, "Yablochkov's candles" appeared on the streets of Paris. Placed in white matte balls, they gave a bright pleasant light. ATshort time wonderful candle Russian inventors behindfought universal recognition. "Yablochkov Candles" illuminated the best hotels, streets and parks of the largest cities in Europe, Accustomed to the dim light of candles and kerosene lamps, people of the last century admired "Yablochkov's candles". New light was called "Russian light", "northern light". Newspapers forWestern European countries wrote: “Light comes to us from the north - from Russia”, “Russia is the birthplace of light”.

Didactic material

Spread of light

As we know, one of the types of heat transfer is radiation. During radiation, the transfer of energy from one body to another can be carried out even in a vacuum. There are several types of radiation, one of them is visible light.

Illuminated bodies gradually heat up. This means that light is indeed radiation.

Light phenomena are studied by the branch of physics called optics. The word "optics" in Greek means "visible", because light is a visible form of radiation.

The study of light phenomena is extremely important for man. After all, more than ninety percent of the information we receive through vision, that is, the ability to perceive light sensations.

Bodies that emit light are called light sources - natural or artificial.

Examples of natural light sources are the Sun and other stars, lightning, luminous insects, and plants. Artificial light sources are a candle, a lamp, a burner and many others.

In any light source, radiation consumes energy.

The sun emits light thanks to the energy from the nuclear reactions occurring in its depths.

A kerosene lamp converts the energy released during the combustion of kerosene into light.

reflection of light

A person sees a light source when a beam from that source enters the eye. If the body is not a source, then the eye can perceive rays from some source reflected by this body, that is, falling on the surface of this body and changing the direction of further propagation. The body that reflects the rays becomes the source of the reflected light.

The rays that fell on the surface of the body change the direction of further propagation. When reflected, the light returns to the same medium from which it fell on the surface of the body. The body that reflects the rays becomes the source of the reflected light.

When we hear this word "reflection", first of all, we are reminded of a mirror. In everyday life, flat mirrors are most often used. With the help of a flat mirror, a simple experiment can be carried out to establish the law by which light is reflected. Let's put the illuminator on a sheet of paper lying on the table in such a way that a thin beam of light lies in the plane of the table. In this case, the light beam will slide over the surface of the sheet of paper, and we will be able to see it.

Let us place a flat mirror vertically in the path of a thin light beam. A beam of light will bounce off it. It can be verified that the reflected beam, like the one incident on the mirror, slides over the paper in the plane of the table. Mark with a pencil on a sheet of paper the relative position of both light beams and the mirror. As a result, we obtain a scheme of the experiment. The angle between the incident beam and the perpendicular restored to the reflecting surface at the point of incidence is usually called the angle of incidence in optics. The angle between the same perpendicular and the reflected beam is the angle of reflection. The results of the experience are:

1. The incident ray, the reflected ray, and the perpendicular to the reflecting surface, reconstructed at the point of incidence, lie in the same plane.
2. The angle of incidence is equal to the angle of reflection. These two conclusions represent the law of reflection.

Looking at a flat mirror, we see images of objects that are located in front of it. These images exactly repeat the appearance of objects. It seems that these twin objects are located behind the surface of the mirror.

Consider the image of a point source in a flat mirror. To do this, we arbitrarily draw several rays from the source, construct the reflected rays corresponding to them, and then complete the continuation of the reflected rays beyond the plane of the mirror. All continuations of the rays will intersect behind the plane of the mirror at one point: this point is the image of the source.

Since it is not the rays themselves that converge in the image, but only their continuations, in reality there is no image at this point: it only seems to us that the rays come from this point. Such an image is called imaginary.

Light refraction

When light reaches the interface between two media, part of it is reflected, while the other part passes through the boundary, being refracted at the same time, that is, changing the direction of further propagation.

A coin immersed in water seems larger to us than when it just lies on the table. A pencil or a spoon placed in a glass of water appears broken to us: the part that is in the water seems to be raised and slightly enlarged. These and many other optical phenomena are explained by the refraction of light.

Refraction of light is due to the fact that light travels at different speeds in different media.

The speed of propagation of light in a particular medium characterizes the optical density of a given medium: the higher the speed of light in a given medium, the lower its optical density.

How will the angle of refraction change when light passes from air to water and when it passes from water to air? Experiments show that when passing from air to water, the angle of refraction is smaller than the angle of incidence. And vice versa: when passing from water to air, the angle of refraction is greater than the angle of incidence.

From experiments on refraction of light, two facts became obvious: 1. The incident beam, the refracted beam, and the perpendicular to the interface between two media, restored at the point of incidence, lie in the same plane.

1. When passing from an optically denser medium to an optically less dense medium, the angle of refraction is greater than the angle of incidence.When passing from an optically less dense medium to an optically denser medium, the angle of refraction is less than the angle of incidence.

An interesting phenomenon can be observed if the angle of incidence is gradually increased when light passes into an optically less dense medium. The angle of refraction in this case is known to be greater than the angle of incidence, and as the angle of incidence increases, the angle of refraction will also increase. At a certain value of the angle of incidence, the angle of refraction will become equal to 90o.

We will gradually increase the angle of incidence as light passes into an optically less dense medium. As the angle of incidence increases, the angle of refraction will also increase. When the angle of refraction becomes ninety degrees, the refracted beam does not pass into the second medium from the first, but slides in the plane of the interface between these two media.

This phenomenon is called total internal reflection, and the angle of incidence at which it occurs is the limiting angle of total internal reflection.

The phenomenon of total internal reflection is widely used in technology. This phenomenon is based on the use of flexible optical fibers, through which light rays pass, repeatedly reflected from the walls.

Light does not escape the fiber due to total internal reflection. A simpler optical device that uses total internal reflection is a reversible prism: it flips the image by swapping the rays entering it.

Image in lenses

A lens whose thickness is small compared to the radii of the spheres forming the surfaces of this lens is called thin. In what follows, we will consider only thin lenses. On optical diagrams, thin lenses are depicted as segments with arrows at the ends. Depending on the direction of the arrows, the diagrams distinguish between converging and diverging lenses.

Let us consider how a beam of rays parallel to the main optical axis passes through the lenses. Coming through

converging lens, the rays are collected at one point. After passing through a diverging lens, the rays diverge in different directions in such a way that all their continuations converge at one point lying in front of the lens.

The point at which, after refraction in a converging lens, rays parallel to the main optical axis are collected is called the main focus of the lens-F.

In a diverging lens, rays parallel to its main optical axis are scattered. The point at which the continuations of the refracted rays are collected lies in front of the lens and is called the main focus of the divergent lens.

The focus of a diverging lens is obtained at the intersection not of the rays themselves, but of their continuations, therefore it is imaginary, in contrast to the converging lens, which has a real focus.

The lens has two main foci. Both of them lie at equal distances from the optical center of the lens on its main optical axis.

The distance from the optical center of the lens to the focus is called the focal length of the lens. The more the lens changes the direction of the rays, the smaller its focal length is. Therefore, the optical power of a lens is inversely proportional to its focal length.

Optical power, as a rule, is denoted by the letter "DE", and is measured in diopters. For example, when writing a prescription for glasses, they indicate how many diopters the optical power of the right and left lenses should be.

diopter (dptr) is the optical power of a lens with a focal length of 1m. Since converging lenses have real foci, and diverging lenses have imaginary foci, we agreed to consider the optical power of converging lenses as a positive value, and the optical power of diverging lenses as negative.

Who established the law of reflection of light?

For the 16th century, optics was an ultra-modern science. From a glass ball filled with water, which was used as a focusing lens, a magnifying glass arose, and from it a microscope and a telescope. The largest maritime power in those days, the Netherlands, needed good telescopes in order to see the dangerous coast ahead of time or get away from the enemy in time. Optics ensured the success and reliability of navigation. Therefore, it was in the Netherlands that many scientists were engaged in it. The Dutchman Willebrord, Snel van Rooyen, who called himself Snellius (1580 - 1626), observed (which, incidentally, many before him had seen) how a thin beam of light was reflected in a mirror. He simply measured the angle of incidence and the angle of reflection of the beam (which no one had done before him) and established the law: the angle of incidence is equal to the angle of reflection.

Source. Mirror world. Gilde V. - M.: Mir, 1982. p. 24.

Why are diamonds valued so highly?

Obviously, a person especially appreciates everything that does not lend itself or is difficult to change. Including precious metals and stones. The ancient Greeks called the diamond "adamas" - irresistible, which expressed their special attitude to this stone. Of course, in rough stones (diamonds were also not cut), the most obvious properties were hardness and brilliance.

Diamonds have a high refractive index; 2.41 for red and 2.47 for violet (for comparison, suffice it to say that the refractive index of water is 1.33, and glass, depending on the grade, from 1.5 to 1.75).

White light is made up of the colors of the spectrum. And when its ray is refracted, each of the constituent colored rays is deflected differently, as if it splits into the colors of the rainbow. That is why there is a "play of colors" in a diamond.

The ancient Greeks were undoubtedly fascinated by this too. Not only is the stone exceptional in brilliance and hardness, it also has the shape of one of Plato's "perfect" solids!

Experiences

EXPERIENCE in optics No. 1

Explain the darkening of a block of wood after wetting it.

Equipment: vessel with water, wooden block.

Explain the vibration of the shadow of a stationary object when light passes through the air above a burning candle. Equipment: tripod, ball on a thread, candle, screen, projector.

Stick colored pieces of paper on the fan blades and observe how the colors add up under different rotation modes. Explain the observed phenomenon.

EXPERIENCE #2

By the interference of light.

A simple demonstration of the absorption of light by an aqueous dye solution

Requires for its preparation only a school illuminator, a glass of water and a white screen. Dyes can be very diverse, including fluorescent.

The students watch with great interest the color change of the white light beam as it propagates through the dye. Unexpected for them is the color of the beam emerging from the solution. Since the light is focused by the lens of the illuminator, the color of the spot on the screen is determined by the distance between the glass of liquid and the screen.

Simple experiments with lenses. (EXPERIMENT No. 3)

What happens to the image of an object obtained with a lens if part of the lens is broken and the image is obtained using the remaining part of it?

Answer . The image will be obtained in the same place where it was obtained with the help of a whole lens, but its illumination will be less, because. a smaller part of the rays coming out of the object will reach its image.

Place a small shiny object on a table lit by the Sun (or a powerful lamp), such as a ball from a bearing, or a bolt from a computer, and look at it through a tiny hole in a piece of foil. Multi-colored rings, or ovals, will be perfectly visible. What kind of phenomenon will be observed? Answer. Diffraction.

Simple experiments with colored glasses. (EXPERIMENT No. 4)

On a white sheet of paper, write “excellent” with a red felt-tip pen or pencil and “good” with a green felt-tip pen. Take two fragments of bottle glass - green and red.

(Attention! be careful, you can get hurt on the edges of the fragments!)

Through which glass do you need to look to see the “excellent” rating?

Answer . It is necessary to look through the green glass. In this case, the inscription will be visible in black on a green paper background, since the red light of the inscription “excellent” is not transmitted by the green glass. When viewed through red glass, the red inscription will not be visible on the red background of the paper.

EXPERIMENT #5: Observation of the phenomenon of dispersion

It is known that when a narrow beam of white light is passed through a glass prism, on a screen installed behind the prism, one can observe a rainbow stripe, which is called the dispersion (or prismatic) spectrum. This spectrum is also observed when the light source, prism and screen are placed in a closed vessel from which the air has been evacuated.

The results of the latest experiment show that there is a dependence of the absolute refractive index of glass on the frequency of light waves. This phenomenon is observed in many substances and is called light dispersion. There are various experiments to illustrate the phenomenon of light dispersion. The figure shows one of the options for its implementation.

The phenomenon of light dispersion was discovered by Newton and is considered one of his most important discoveries. The tombstone erected in 1731 depicts the figures of young men holding the emblems of Newton's most important discoveries. In the hands of one of the young men there is a prism, and in the inscription on the monument there are the following words: "He investigated the difference of light rays and the various properties of colors manifested in this, which no one had suspected before."

EXPERIENCE #6: Does a mirror have memory?

How to put a flat mirror on a drawn rectangle to get an image: triangle, quadrangle, pentagon. Equipment: a flat mirror, a sheet of paper with a square drawn on it.

QUESTIONS

Transparent plexiglass becomes opaque if its surface is rubbed with sandpaper. The same glass becomes transparent again when rubbed....How?

Numbers equal to the ratio of the focal length to the aperture diameter are marked on the lens aperture scale: 2; 2.8; 4.5; 5; 5.8, etc. How will the exposure time change if the aperture is moved to a larger division of the scale?

Answer. The larger the aperture number indicated on the scale, the lower the illumination of the image, and the longer the shutter speed required for photographing.

Most often, camera lenses consist of several lenses. Light passing through the lens is partially reflected from the surfaces of the lenses. What kind of defects does this lead to when shooting?Answer

When shooting snow plains and water surfaces on sunny days, it is recommended to use a solar hood, which is a cylindrical or conical tube blackened inside, worn on
lens. What is the purpose of the hood?Answer

To prevent light from being reflected inside the lens, a very thin transparent film of the order of ten-thousandths of a millimeter is applied to the lens surface. Such lenses are called enlightened. What physical phenomenon is the lens coating based on? Explain why lenses do not reflect light.Answer.

Question for forum

Why does black velvet seem so much darker than black silk?

Why doesn't white light break down into its components when it passes through a window pane?Answer.

Blitz

1. What are glasses without temples called? (pince-nez)

2. What gives an eagle during the hunt? (Shadow.)

3. Why is the artist Kuinzhi famous? (The ability to depict the transparency of air and moonlight)

4. What are the lamps that light up the stage called? (soffits)

5. Is the gem blue or greenish?(Turquoise)

6. Indicate at what point the fish is in the water if the fisherman sees it at point A.

Blitz

1. What can't you hide in a chest? (A ray of light)

2. What color is white light? (White light consists of a series of multi-colored rays: red, orange, yellow, green, blue, indigo, violet)

3. What is more: a cloud or a shadow from it? (The cloud casts a cone of full shadow narrowing towards the ground, the height of which is large due to the significant size of the cloud. Therefore, the shadow of the cloud differs little in size from the cloud itself)

4. You follow her, she follows you, you follow her, she follows you. What it is? (Shadow)

5. The edge is visible, but you will not reach it. What is it? (horizon)

Optical illusions.

Don't you think that the black and white stripes are moving in opposite directions? If you tilt your head - then to the right, then to the left - the direction of rotation also changes.

An endless staircase leading up.

sun and eye

do not be like the Sun of the eyes,

He couldn't see the sun... W. Goethe

The juxtaposition of the eye and the sun is as old as the human race itself. The source of such a comparison is not science. And in our time, side by side with science, simultaneously with the picture of phenomena revealed and explained by the new natural science, the world of ideas of the child and primitive man continues to exist, and, intentionally or unintentionally, the world of poets imitating them. It is sometimes worth looking into this world as one of the possible sources of scientific hypotheses. He is amazing and fabulous; in this world, bridges-connections are boldly thrown between the phenomena of nature, of which science sometimes does not yet suspect. In some cases, these connections are guessed correctly, sometimes they are fundamentally erroneous and simply ridiculous, but they always deserve attention, since these errors often help to understand the truth. Therefore, it is instructive to approach the question of the connection between the eye and the Sun first from the point of view of children's, primitive and poetic ideas.

Playing "hide and seek", the child very often decides to hide in the most unexpected way: he closes his eyes or covers them with his hands, being sure that now no one will see him; for him vision is identified with light.

Even more surprising, however, is the persistence of the same instinctive confusion of vision and light in adults. Photographers, that is, people who are somewhat experienced in practical optics, often catch themselves closing their eyes when, when loading or developing plates, care must be taken that light does not penetrate into a dark room.

If you carefully listen to how we speak, to our own words, then here, too, traces of the same fantastic optics are immediately found.

Without noticing this, people say: "the eyes sparkled", "the sun came out", "the stars are watching."

For poets, the transfer of visual representations to the luminary and, conversely, attributing the properties of light sources to the eyes is the most common, one might say, obligatory technique:

Stars of the night

Like accusatory eyes

They look at him mockingly.

His eyes are shining.

A.S. Pushkin.

We looked at the stars with you

They are on us. Fet.

How do fish see you?

Due to the refraction of light, the fisherman sees the fish not where it actually is.

Folk omens