Logopedic portal / Techniques / Optics. Shadow. Reflection of light. Light refraction. Experiences. Features of the phenomenon of light refraction from the point of view of physics Experience in refraction of light at home

Optics. Shadow. Reflection of light. Light refraction. Experiences. Features of the phenomenon of light refraction from the point of view of physics Experience in refraction of light at home

10.02.2023

Class: 11

The mind is not only in knowledge, but also in the ability to apply knowledge in practice.
Aristotle.

Lesson Objectives:

check knowledge of the laws of reflection;
teach to measure the refractive index of glass using the law of refraction;
development of skills for independent work with equipment;
development of cognitive interests in the preparation of a message on the topic;
development of logical thinking, memory, the ability to subordinate attention to the performance of tasks.
education of accurate work with equipment;
fostering cooperation in the process of joint implementation of tasks.

Interdisciplinary connections: physics, mathematics, literature.

Lesson type: learning new material, improving and deepening knowledge, skills and abilities.

Equipment:

Instruments and materials for laboratory work: a high glass with a capacity of 50 ml, a glass plate (prism) with oblique edges, a test tube, a pencil.
A cup of water with a coin at the bottom; thin glass beaker.
Test tube with glycerin, glass rod.
Cards with an individual task.

Demonstration: Light refraction. total internal reflection.

DURING THE CLASSES.

I. Organizational moment. The topic of the lesson.

Teacher: Guys, we have moved on to studying the section of physics "Optics", which studies the laws of light propagation in a transparent medium based on the concept of a light beam. Today you will learn that the law of refraction of waves is also valid for light.

So, the purpose of today's lesson is to study the law of refraction of light.

II. Updating of basic knowledge.

1. What is a light beam? (The geometric line that indicates the direction of light propagation is called a light ray.)

The nature of light is electromagnetic. One proof of this is the coincidence of the speeds of electromagnetic waves and light in vacuum. When light propagates in a medium, it is absorbed and scattered, and at the interface between the media it is reflected and refracted.

Let's repeat the laws of reflection. ( Individual tasks are distributed on cards).

Card 1.
Construct a reflected ray in the notebook.

Card 2.
Are the reflected rays parallel?

Card 3.
Build a reflective surface.

Card 4.
The angle between the incident beam and the reflected beam is 60°. What is the angle of incidence? Draw in a notebook.

Card 5.
A man with a height of H = 1.8 m, standing on the shore of the lake, sees the reflection of the Moon in the water, which is at an angle of 30 ° to the horizon. At what distance from the shore can a person see the reflection of the moon in the water?

2. Formulate the law of light propagation.

3. What phenomenon is called the reflection of light?

4. Draw on the board a light beam falling on a reflective surface; angle of incidence; draw the reflected ray, the angle of reflection.

5. Why do window panes appear dark from a distance when viewed on a clear day from the street?

6. How should a flat mirror be positioned so that a vertical beam is reflected horizontally?

And at noon puddles under the window
So spill and shine
What a bright sunspot
The bunnies are fluttering around the hall.
I.A. Bunin.

Explain from the point of view of physics the observed phenomenon described by Bunin in a quatrain.

Checking the performance of tasks on the cards.

III. Explanation of new material.

At the interface between two media, light falling from the first medium is reflected back into it. If the second medium is transparent, then the light can partially pass through the boundary of the media. In this case, as a rule, it changes the direction of propagation, or experiences refraction.

The refraction of waves during the transition from one medium to another is caused by the fact that the speeds of wave propagation in these media are different.

Perform the experiments "Observation of the refraction of light."

Place a pencil vertically in the middle of the bottom of an empty glass and look at it so that its lower end, the edge of the glass and the eye are on the same line. Without changing the position of the eyes, pour water into a glass. Why is it that as the water level in the glass rises, the visible part of the bottom increases noticeably, while the pencil and the bottom seem to be raised?
Position the pencil obliquely in a glass of water and look at it from above and then from the side. Why does a pencil appear broken at the surface of the water when viewed from above?
Why, when viewed from the side, the part of the pencil located in the water seems to be shifted to the side and increased in diameter?
This is all due to the fact that when passing from one transparent medium to another, the light beam is refracted.
Observation of the deflection of a laser flashlight beam when passing through a plane-parallel plate.

The incident beam, the refracted beam, and the perpendicular to the interface between two media, restored at the point of incidence of the beam, lie in the same plane; the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for two media, called the relative refractive index of the second medium relative to the first.

The refractive index relative to vacuum is called absolute index of refraction.

In the collection of tasks, find the table "The refractive index of substances." Please note that glass, diamond have a higher refractive index than water. Why do you think? Solids have a denser crystal lattice, it is more difficult for light to pass through it, so substances have a higher refractive index.

A substance with a higher refractive index n 1 is called optically denser environment if n 1 > n 2. A substance with a lower refractive index n 1 is called optically less dense environment if n 1< n 2 .

IV. Consolidation of the topic.

2. Solving problems No. 1395.

3. Laboratory work "Determination of the refractive index of glass."

Equipment: A glass plate with plane-parallel edges, a plank, a protractor, three pins, a pencil, a square.

The order of the work.

As an epigraph to our lesson, I picked up the words of Aristotle "The mind is not only in knowledge, but also in the ability to apply knowledge in practice." I think doing the lab correctly is proof of these words.

v.

Many dreams of antiquity have long been realized, and many fabulous magics have become the property of science. Lightnings are caught, mountains are drilled, they fly on "flying carpets" ... Is it possible to invent an "invisibility cap", i.e. find a way to make bodies completely invisible? We will talk about this now.

The ideas and fantasies of the English novelist G. Wells about the invisible man 10 years later, the German anatomist - Professor Shpaltegolts put into practice - though not for living organisms, but for dead drugs. Many museums around the world now display these transparent preparations of body parts, even whole animals. The method for the preparation of transparent preparations, developed in 1941 by Professor Shpaltegolts, consists in the fact that after a known bleaching and washing treatment, the preparation is impregnated with salicylic acid methyl ester (it is a colorless liquid with strong birefringence). The preparation of rats, fish, parts of the human body prepared in this way is immersed in a vessel filled with the same liquid. At the same time, of course, they do not strive to achieve complete transparency, because then they would become completely invisible, and therefore useless for the anatomist. But if you wish, you can achieve this. First, it is necessary to find a way to saturate the tissues of a living organism with an enlightening liquid. Secondly, Spaltegoltz preparations are only transparent, but not invisible only as long as they are immersed in a vessel with a liquid. But let us suppose that in time both of these obstacles can be overcome and, consequently, the dream of the English novelist can be put into practice.

You can repeat the experience of the inventor with a glass rod - the "invisible wand". A glass rod is inserted into the flask with glycerin through the cork, the part of the rod immersed in glycerin becomes invisible. If the flask is turned over, then the other part of the stick becomes invisible. The observed effect is easily explained. The refractive index of glass is almost equal to the refractive index of glycerol, therefore, neither refraction nor reflection of light occurs at the interface between these substances.

Full reflection.

If light passes from an optically denser medium to an optically less dense medium (in the figure), then at a certain angle of incidence α0, the angle of refraction β becomes equal to 90°. The intensity of the refracted beam in this case becomes equal to zero. Light falling on the interface between two media is completely reflected from it. There is total reflection.

The angle of incidence α0 at which total internal reflection light is called limiting angle total internal reflection. At all angles of incidence equal to or greater than α0, total reflection of light occurs.

The value of the limiting angle is found from the relation . If n 2 \u003d 1 (vacuum, air), then.

Experiments "Observation of the total reflection of light."

1. Place the pencil obliquely in a glass of water, raise the glass above eye level and look down through the glass at the surface of the water. Why does the surface of water in a glass look like a mirror when viewed from below?

2. Dip an empty test tube into a glass of water and look at it from above. Does the part of the test tube immersed in water seem shiny?

3. Do at home experience " Making the coin invisible. You will need a coin, a bowl of water and a clear glass. Put a coin on the bottom of the bowl and note the angle at which it is visible from the outside. Without taking your eyes off the coin, slowly lower an inverted empty transparent glass from above into the bowl, holding it strictly vertically so that water does not pour inside. Explain the observed phenomenon in the next lesson.

(At some point, the coin will disappear! When you lower the glass, the water level in the bowl rises. Now, to exit the bowl, the beam must pass the water-air interface twice. After passing the first boundary, the angle of refraction will be significant, so that at the second boundary there will be total internal reflection (the light no longer exits the bowl, so you can't see the coin.)

For the glass-air interface, the angle of total internal reflection is: .

Limit angles of total reflection.

Diamond…24º
Petrol….45º
Glycerin…45º
Alcohol…47º
Glass of different grades …30º-42º
Ether…47º

The phenomenon of total internal reflection is used in fiber optics.

Experiencing total internal reflection, the light signal can propagate inside a flexible glass fiber (optical fiber). Light can leave the fiber only at large initial angles of incidence and with a significant bending of the fiber. The use of a beam consisting of thousands of flexible glass fibers (with a diameter of each fiber from 0.002-0.01 mm) makes it possible to transmit optical images from the beginning to the end of the beam.

Fiber optics is a system for transmitting optical images using glass fibers (glass guides).

Fiber optic devices are widely used in medicine as endoscopes- probes inserted into various internal organs (bronchial tubes, blood vessels, etc.) for direct visual observation.

Currently, fiber optics is replacing metal conductors in information transmission systems.

An increase in the carrier frequency of the transmitted signal increases the amount of information transmitted. The frequency of visible light is 5-6 orders of magnitude higher than the carrier frequency of radio waves. Accordingly, a light signal can transmit a million times more information than a radio signal. The necessary information is transmitted via a fiber cable in the form of modulated laser radiation. Fiber optics is necessary for fast and high-quality transmission of a computer signal containing a large amount of transmitted information.

Total internal reflection is used in prismatic binoculars, periscopes, reflex cameras, as well as in reflectors (reflectors) that ensure safe parking and movement of cars.

Summarizing.

In today's lesson, we got acquainted with the refraction of light, learned what the refractive index is, determined the refractive index of a plane-parallel glass plate, got acquainted with the concept of total reflection, learned about the use of fiber optics.

Homework.

We have considered the refraction of light at flat boundaries. In this case, the size of the image remains equal to the size of the object. In the next lessons, we will look at the passage of a light beam through lenses. It is necessary to repeat the structure of the eye from biology.

Bibliography:

G.Ya. Myakishev. B.B. Bukhovtsev. Physics textbook grade 11.
V.P. Demkovich, L.P. Demkovich. Collection of problems in physics.
Ya.I. Perelman. Entertaining tasks and experiences.
AND I. Lanina. Not a single lesson .

Every day we encounter various physical phenomena. One of them is light. Today I will write about some experiments with light that we conducted together with my son Vladik.

Before conducting experiments with light, it is important to highlight some of its properties.

One of the properties is straightness of its distribution . Only in this case, the formation of a shadow is possible. The subject of shadows is very interesting. you can play shadow theater, you can watch the long shadow in the morning, afternoon and evening. For older children, it is interesting to consider the projections of three-dimensional objects. For example, the shadow of a cone can be a triangle and a circle.

Another property is ability of light to reflect from barriers. If the rays fall on the mirror, they are reflected so that we see the object in full size. If the rays fall on an uneven surface, they are reflected in all directions and make this surface illuminated. That is why we see objects that themselves do not glow. Knowing about the ability of rays to reflect, we will conduct an experiment. Let's turn an ordinary egg into a silver one

We will need:

boiled egg,
candle,
a glass of water.

An egg was smoked over a candle flame. It turned out velvety black! Then they plunged him into the water. It shone like silver! The fact is that soot particles are poorly wetted by water. A film has formed around the egg, which, like a mirror, reflects the rays of light.

An interesting fact related to the reflectivity of light. A mirage in the desert is formed as a result of the fact that a heated layer of air adjacent to hot sand acquires mirror properties. Also, asphalt roads get very hot in the sun, and their surface from a distance seems to be watered with water and reflects objects.

Another interesting point. It is usually thought that the North and South Poles are cold because they get little heat from the Sun. This is not true. Antarctica receives annually as much solar energy as countries equal in area to it, located in the equatorial zone. But it returns 90% of this heat to the outer space. The snow shell that covers Antarctica acts like a giant mirror reflecting the life-giving rays of the sun.

When rays of light enter from the air into some other transparent medium, they are refracted. This is easy to see if you look at a glass with chopsticks or a spoon. The sticks are broken. This really surprised our child!

Refraction of rays at the boundary of two media

We will need:

water glass,
beam of light (if there is no beam of natural light, you can use a flashlight)

Rays passing through glass gather in a bundle, and then fan out. So the refraction of rays occurs at the boundary of two media. The fact that the rays are collected in a beam, we observe when we use a lens for burning.

The husband enthusiastically talked about how he and his brothers burned out on the bench with the help of a lens.

Often, when a ray of light is refracted, one can observe its decomposition into seven colors. This is the phenomenon of dispersion. The colors are always in a certain order. Such a sequence is called a spectrum. Dispersion is also observed in nature - it is a rainbow.

And we got a rainbow at home

In everyday life, we meet with various optical devices - from our grandmothers' glasses to a microscope, magnifying glasses. And every day we look in the mirror, and with their help you can spend

You can get a rainbow at home with the help of water. I talk about this in detail in the book “Home Lab. Experiments with water. And I give you this book. Download now, delight and surprise children. Explore the fascinating world of science together. Send photos of your brightest and most memorable experiences and experiments. With the help of simple objects, you can conduct interesting experiments. It is about such that we talk about on the pages of Merry Science. Thank you for being with us and see you soon.

Successful experiments! Science is fun!

The Greek astronomer Claudius Ptolemy (circa 130 AD) is the author of a remarkable book that served as the main textbook on astronomy for almost 15 centuries. However, in addition to the astronomical textbook, Ptolemy also wrote the book Optics, in which he outlined the theory of vision, the theory of flat and spherical mirrors, and the study of the phenomenon of light refraction. Ptolemy encountered the phenomenon of light refraction while observing the stars. He noticed that a beam of light, passing from one medium to another, "breaks". Therefore, a stellar ray, passing through the earth's atmosphere, reaches the surface of the earth not in a straight line, but along a curved line, that is, refraction occurs. The curvature of the beam path occurs due to the fact that the air density changes with height.

To study the law of refraction, Ptolemy conducted the following experiment. He took the circle and fixed the rulers l1 and l2 on the axis so that they could freely rotate around it (see figure). Ptolemy immersed this circle in water up to the diameter AB and, turning the lower ruler, ensured that the rulers lay for the eye on one straight line (if you look along the upper ruler). After that, he took the circle out of the water and compared the angles of incidence α and refraction β. He measured angles with an accuracy of 0.5°. The numbers obtained by Ptolemy are presented in the table.

Ptolemy did not find a "formula" of the relationship for these two series of numbers. However, if you determine the sines of these angles, it turns out that the ratio of the sines is expressed by almost the same number, even with such a rough measurement of the angles that Ptolemy resorted to.

Due to the refraction of light in a calm atmosphere, the apparent position of the stars in the sky relative to the horizon

1) above actual position

2) below actual position

3) shifted in one direction or another vertically relative to the actual position

4) matches the actual position

End of form

Form start

In a calm atmosphere, the positions of stars that are not perpendicular to the surface of the Earth at the point where the observer is located are observed. What is the apparent position of the stars - above or below their actual position relative to the horizon? Explain the answer.

End of form

Form start

Refraction in the text refers to the phenomenon

1) changes in the direction of propagation of a light beam due to reflection at the boundary of the atmosphere

2) changes in the direction of propagation of a light beam due to refraction in the Earth's atmosphere

3) absorption of light as it propagates through the earth's atmosphere

4) light beam bending around obstacles and thus deflecting rectilinear propagation

End of form

Form start

Which of the following conclusions contradicts Ptolemy's experiments?

1) the angle of refraction is less than the angle of incidence when the beam passes from air to water

2) as the angle of incidence increases, the angle of refraction increases linearly

3) the ratio of the sine of the angle of incidence to the sine of the angle of refraction does not change

4) the sine of the angle of refraction depends linearly on the sine of the angle of incidence

End of form

Photoluminescence

Some substances, when illuminated by electromagnetic radiation, begin to glow themselves. This glow, or luminescence, has an important feature: the luminescence light has a different spectral composition than the light that caused the glow. Observations show that luminescence light has a longer wavelength than the exciting light. For example, if a beam of violet light is directed to a cone with a solution of fluorescein, then the illuminated liquid begins to luminesce brightly with green-yellow light.

Some bodies retain the ability to glow for some time after their illumination has ceased. Such an afterglow can have a different duration: from fractions of a second to many hours. It is customary to call a glow that stops with lighting, fluorescence, and a glow that has a noticeable duration, phosphorescence.

Phosphorescent crystalline powders are used to coat special screens that remain luminous for two to three minutes after illumination. Such screens also glow under the action of X-rays.

Phosphorescent powders have found a very important application in the manufacture of fluorescent lamps. In gas-discharge lamps filled with mercury vapor, when an electric current passes, ultraviolet radiation is produced. Soviet physicist S.I. Vavilov proposed to cover the inner surface of such lamps with a specially made phosphorescent composition, which, when irradiated with ultraviolet, gives visible light. By selecting the composition of the phosphorescent substance, it is possible to obtain the spectral composition of the emitted light, as close as possible to the spectral composition of daylight.

The phenomenon of luminescence is characterized by extremely high sensitivity: sometimes 10 - - 10 g of a luminous substance, for example, in solution, is enough to detect this substance by its characteristic glow. This property is the basis of luminescent analysis, which makes it possible to detect negligible impurities and to judge about impurities or processes that lead to a change in the original substance.

Human tissues contain a wide variety of natural fluorophores, which have different fluorescence spectral regions. The figure shows the emission spectra of the main fluorophores of biological tissues and the scale of electromagnetic waves.

According to the given data, pyroxidine glows

1) red light

2) yellow light

3) green light

4) purple light

End of form

Form start

Two identical crystals, having the property of phosphorescence in the yellow part of the spectrum, were preliminarily illuminated: the first with red rays, the second with blue rays. For which of the crystals will it be possible to observe an afterglow? Explain the answer.

End of form

Form start

When examining food products, the luminescent method can be used to detect spoilage and falsification of products.
The table shows the indicators of the luminescence of fats.

Butter luminescence color changed from yellow-green to blue. This means that the butter could have added

1) only butter margarine

2) only margarine "Extra"

3) only vegetable fat

4) any of the specified fats

End of form

Earth Albedo

The temperature at the Earth's surface depends on the reflectivity of the planet - albedo. Surface albedo is the ratio of the energy flux of reflected sunlight to the energy flux of solar rays incident on the surface, expressed as a percentage or fraction of a unit. The Earth's albedo in the visible part of the spectrum is about 40%. In the absence of clouds, it would be about 15%.

Albedo depends on many factors: the presence and condition of cloudiness, changes in glaciers, seasons, and, accordingly, on precipitation.

In the 90s of the XX century, the significant role of aerosols - "clouds" of the smallest solid and liquid particles in the atmosphere became obvious. When fuel is burned, gaseous oxides of sulfur and nitrogen enter the air; combining in the atmosphere with water droplets, they form sulfuric, nitric acids and ammonia, which then turn into sulfate and nitrate aerosols. Aerosols not only reflect sunlight without letting it through to the Earth's surface. Aerosol particles serve as nuclei for the condensation of atmospheric moisture during the formation of clouds and thereby contribute to an increase in cloudiness. And this, in turn, reduces the influx of solar heat to the earth's surface.

Transparency for solar rays in the lower layers of the earth's atmosphere also depends on fires. Due to fires, dust and soot rise into the atmosphere, which cover the Earth with a dense screen and increase the surface albedo.

Which statements are true?

A. Aerosols reflect sunlight and thus contribute to a decrease in the Earth's albedo.

B. Volcanic eruptions contribute to an increase in the Earth's albedo.

1) only A

2) only B

3) both A and B

4) neither A nor B

End of form

Form start

The table shows some characteristics for the planets of the solar system - Venus and Mars. It is known that the albedo of Venus A 1= 0.76, and the albedo of Mars A 2= 0.15. Which of the characteristics mainly influenced the difference in the albedo of the planets?

1) A 2) B 3) IN 4) G

End of form

Form start

Does the Earth's albedo increase or decrease during volcanic eruptions? Explain the answer.

End of form

Form start

Surface albedo is understood as

1) the total amount of sunlight falling on the earth's surface

2) the ratio of the energy flux of reflected radiation to the flux of absorbed radiation

3) the ratio of the energy flux of reflected radiation to the flux of incident radiation

4) the difference between the incident and reflected radiation energy

End of form

Spectra study

All heated bodies radiate electromagnetic waves. To experimentally investigate the dependence of the radiation intensity on the wavelength, it is necessary:

1) expand the radiation into a spectrum;

2) measure the energy distribution in the spectrum.

To obtain and study spectra, spectral devices - spectrographs - are used. The scheme of the prism spectrograph is shown in the figure. The studied radiation first enters the tube, at one end of which there is a screen with a narrow slit, and at the other end there is a converging lens L 1 . The slit is at the focus of the lens. Therefore, a divergent light beam that enters the lens from the slit exits it in a parallel beam and falls on the prism R.

Since different frequencies correspond to different refractive indices, parallel beams of different colors come out of the prism, which do not coincide in direction. They fall on the lens L 2. At the focal length of this lens is a screen, frosted glass or photographic plate. Lens L 2 focuses parallel beams of rays on the screen, and instead of a single image of the slit, a whole series of images is obtained. Each frequency (more precisely, a narrow spectral interval) has its own image in the form of a colored strip. All these images together
and form a spectrum.

The radiation energy causes the body to heat up, so it is enough to measure the body temperature and use it to judge the amount of energy absorbed per unit time. As a sensitive element, one can take a thin metal plate covered with a thin layer of soot, and by heating the plate one can judge the radiation energy in a given part of the spectrum.

The decomposition of light into a spectrum in the apparatus shown in the figure is based on

1) light dispersion phenomenon

2) phenomenon of light reflection

3) light absorption phenomenon

4) thin lens properties

End of form

Form start

In the device of a prism spectrograph, the lens L 2 (see figure) is used for

1) decomposition of light into a spectrum

2) focusing rays of a certain frequency into a narrow strip on the screen

3) determining the intensity of radiation in different parts of the spectrum

4) converting a divergent light beam into parallel beams

End of form

Form start

Is it necessary to cover the metal plate of the thermometer used in the spectrograph with a layer of soot? Explain the answer.

End of form

Form start

Physics lesson in grade 11 on the topic "Refraction of light".

Lesson Objectives:

check knowledge of the laws of reflection;

teach to measure the refractive index of glass using the law of refraction;

development of skills for independent work with equipment;

development of logical thinking, memory, the ability to subordinate attention to the performance of tasks.

education of accurate work with equipment;

fostering cooperation in the process of joint implementation of tasks.

Interdisciplinary connections: physics, mathematics, literature.

Lesson type: learning new material, improving and deepening knowledge, skills and abilities.

Equipment:

Instruments and materials for laboratory work: a high glass with a capacity of 50 ml, a glass plate (prism) with oblique edges, a test tube, a pencil.

A cup of water with a coin at the bottom; thin glass beaker.

Test tube with glycerin, glass rod.

Cards with an individual task.

Demonstration: Light refraction. total internal reflection.

DURING THE CLASSES.

I. Organizational moment. The topic of the lesson.

So, the purpose of today's lesson is to study the law of refraction of light.

II. Updating of basic knowledge.

1. What is a light beam? (The geometric line that indicates the direction of propagation of light energy is called a light beam.)

Let's repeat the laws of reflection. (ORAL: tasks prepared on the interactive whiteboard)

Card 1.
Construct a reflected ray in the notebook.

Card 2.
Are the reflected rays parallel?

Card 3.
Build a reflective surface.

Card 4.
The angle between the incident beam and the reflected beam is 60°. What is the angle of incidence? Draw in a notebook.

2. Formulate the law of light propagation.

And at noon puddles under the window
So spill and shine
What a bright sunspot
The bunnies are fluttering around the hall.
I.A. Bunin.

Explain from the point of view of physics the observed phenomenon described by Bunin in a quatrain.

Checking the performance of tasks on the cards.

III. Explanation of new material.

The refraction of waves during the transition from one medium to another is caused by the fact that the speeds of wave propagation in these media are different.

Perform the experiments "Observation of the refraction of light."

Position the pencil obliquely in a glass of water and look at it from above and then from the side. Why does a pencil appear broken at the surface of the water when viewed from above?
Why, when viewed from the side, the part of the pencil located in the water seems to be shifted to the side and increased in diameter?
This is all due to the fact that when passing from one transparent medium to another, the light beam is refracted.

Observation of the deflection of a laser flashlight beam when passing through a plane-parallel plate.

The refractive index relative to vacuum is called absolute index of refraction.

IV. Consolidation of the topic.

2. Solving problems No. 1395.

3. Laboratory work "Determination of the refractive index of glass."

Equipment: A glass plate with plane-parallel edges, a plank, a protractor, three pins, a pencil, a square.

The order of the work.

v.

Full reflection.

The value of the limiting angle is found from the relation . If n 2 \u003d 1 (vacuum, air), then.

Experiments "Observation of the total reflection of light."

2. Dip an empty test tube into a glass of water and look at it from above. Does the part of the test tube immersed in water seem shiny?

For the glass-air interface, the angle of total internal reflection is: .

Limit angles of total reflection.

Diamond…24º
Petrol….45º
Glycerin…45º
Alcohol…47º
Glass of different grades …30º-42º
Ether…47º

Fiber optics is a system for transmitting optical images using glass fibers (glass guides).

Fiber optic devices are widely used in medicine as endoscopes- probes inserted into various internal organs (bronchial tubes, blood vessels, etc.) for direct visual observation.

Currently, fiber optics is replacing metal conductors in information transmission systems.

Total internal reflection is used in prismatic binoculars, periscopes, reflex cameras, as well as in reflectors (reflectors) that ensure safe parking and movement of cars.

Summarizing.

Homework.

Bibliography:

G.Ya. Myakishev. B.B. Bukhovtsev. Physics textbook grade 11.

V.P. Demkovich, L.P. Demkovich. Collection of problems in physics.

Ya.I. Perelman. Entertaining tasks and experiences.

AND I. Lanina. Not a single lesson .

In the previous lessons, you got acquainted with the basic laws of light propagation: the laws of reflection and refraction. But, as you know, a person seeks to use any comprehended law in practice. If for two media the refractive index remains constant, can we, for example, determine the substance of one medium, knowing the substance of the other from the angle of deflection of the light beam when passing through the interface between these media? How to do this in practice, you will learn from this lesson on laboratory work.

Theme: Optics

Lesson: Practical work on the topic "Determination of the refractive index of glass"

Goal of the work : determination of the relative refractive index of glass using a plane-parallel plate.

Rice. 1. Definition of the indicator

sinα - angle of incidence

sinγ - angle of refraction

There are two horizontal lines in the figure: a small and a large face of a plane-parallel plate (see Fig. 1).

The first pin is located at point O. The second pin is located at point A. The direction of AO is the direction of the incident beam.

The direction from point O to a pin located on a large face is a refracted ray.

Let us measure the distance OD = OA with a ruler.

From point A to the perpendicular of the separation of two media, we lower the perpendicular. From point D to the perpendicular of the separation of two media, we lower the perpendicular.

The two triangles are right angled. They can determine the sine of the angle of incidence and the sine of the angle of refraction.

With the help of a ruler, the distance AC and the distance DB are measured.

Several measurements need to be taken. To do this, you need to change the location of the second pin at any other angle. As a result, the angle of incidence and the angle of refraction will change, but the refractive index will be constant for these two media.

1 way

Equipment : a plane-parallel plate, 3 pins, a ruler, a protractor, a sheet of paper, a pencil, a piece of foam rubber.

Progress:

1. Put a piece of foam rubber on the table to make it easier to stick the pins.

2. Cover the foam rubber with a white sheet of paper.

3. Put a plane-parallel glass plate on top.

4. Draw a pencil around the small and large faces.

5. We will stick the first pin near the first face, we will stick the second pin at some angle to the first.

6. Observing the two pins through the large edge, find the location of the third pin so that the first and second block each other (see Fig. 2).

Rice. 2. Plane plate

7. Mark the location of all three pins.

8. We remove the equipment and look at the resulting drawing.

9. Using a ruler, we measure the legs (see Fig. 3).

Rice. 3. Definition of the indicator

CA = 15 mm, DB = 10 mm.

For a more accurate result, you need to perform several experiments.

The relative refractive index is 1.5, which means that the speed of light when passing from air to glass decreases by 1.5 times.

To verify the obtained data, it is necessary to compare them with a table of refractive indices for various substances (see Fig. 4).

Rice. 4. Table of refractive indices

By the index of refraction, we can determine what kind of substance we have.

2 way

Equipment: a light bulb, a screen with a slit, a sheet of paper.

Progress:

1. Using wires, we connect a galvanic cell (battery) with an incandescent bulb.

2. We put a screen with a slit in front of the lamp, and behind it we put a plane-parallel plate.

3. We measure the angle of incidence and the angle of refraction using a protractor.

4. Using the Bradis table, we find the values of the sines in the corners.

5. Calculate the refractive index (see Fig. 5).

Rice. 5. Plane plate

An example of calculating the error

Error:

1. Absolute.

2. Relative.

Absolute errors: measuring device, measurement

In a metal ruler, the error can be considered half the division value of this measuring device, i.e. 0.5 mm.

The measurement error can also be half the division value of the ruler (0.5 mm).

In general, the absolute error is 1 mm.

Relative error (ε) (see Fig. 6):

Rice. 6. Relative error

Determination of the absolute error of the measured refractive index (see Fig. 7):

Rice. 7. Absolute error

1. Nizhny Novgorod branch of MIIT ( ).

1. We conduct experiments on the refraction of light

Let's conduct such an experiment. Let us direct a narrow beam of light at the surface of water in a wide vessel at a certain angle to the surface. We will notice that at the points of incidence, the rays are not only reflected from the surface of the water, but also partially pass into the water, while changing their direction (Fig. 3.33).

The change in the direction of propagation of light in the case of its passage through the interface between two media is called refraction of light.

The first mention of the refraction of light can be found in the works of the ancient Greek philosopher Aristotle, who wondered: why does a stick seem broken in water? And in one of the ancient Greek treatises, such an experience is described: “You need to stand up so that the flat ring placed on the bottom of the vessel is hidden behind its edge. Then, without changing the position of the eyes, pour water into the vessel.

Rice. 3.33 Scheme of the experiment to demonstrate the refraction of light. Passing from air into water, a ray of light changes its direction, shifting towards the perpendicular, restored at the point of incidence of the ray

2. There are such relationships between the angle of incidence and the angle of refraction:

a) in the case of an increase in the angle of incidence, the angle of refraction also increases;

b) if a beam of light passes from a medium with a lower optical density to a medium with a higher optical density, then the angle of refraction will be less than the angle of incidence;

c) if a beam of light passes from a medium with a higher optical density to a medium with a lower optical density, then the angle of refraction will be greater than the angle of incidence.

(It should be noted that in high school, after studying the course of trigonometry, you will become more familiar with the refraction of light and learn about it at the level of laws.)

4. We explain some optical phenomena by the refraction of light

When we, standing on the shore of a reservoir, try to determine its depth by eye, it always seems smaller than it actually is. This phenomenon is explained by the refraction of light (Fig. 3.37).

Rice. 3. 39. Optical devices based on the phenomenon of light refraction

Control questions

1. What phenomenon do we observe when light passes through the interface between two media?

L. I. Mandelstam studied the propagation of electromagnetic waves, primarily of visible light. He discovered a number of effects, some of which now bear his name (Raman scattering of light, the Mandelstam-Brillouin effect, etc.).

Related materials:

Site Map