A virtual image of an object (we cannot place a photographic plate behind a mirror and register it). It is you, and in the mirror it is not you, but your image. What is the difference?
Demonstration with candles and flat mirror. A piece of glass is placed vertically against the background of a black screen. Electric lamps (candles) are placed on stands in front of and behind the glass at equal distances. If one is on fire, then it seems that the other is also on fire.
Distances from an object to a flat mirror ( d) and from the mirror to the image of the object ( f) are equal: d = f. Equal size of object and image. Object vision area(show on drawing).
“No, no one, Mirrors, has comprehended you, no one has yet penetrated your soul.”
“Two people look down, one sees a puddle, the other sees the stars reflected in it.”
Dovzhenko
Convex and concave mirrors (demonstration with FOS-67 and a steel ruler). Constructing an image of an object in a convex mirror. Applications of spherical mirrors: car headlights (like the Ostyaks catch fish), car side mirrors, solar stations, satellite dishes.
IV. Tasks:
1. A flat mirror and some object AB are located as shown in the figure. Where should the observer's eye be located so that the entire image of the object in the mirror is visible?
2. The sun's rays make an angle of 62 0 with the horizon. How should a flat mirror be positioned in relation to the ground in order to direct the rays horizontally? (Consider all 4 cases).
3. The bulb of a table lamp is located at a distance of 0.6 m from the surface of the table and at a distance of 1.8 m from the ceiling. On the table lies a fragment of a flat mirror in the shape of a triangle with sides of 5 cm, 6 cm and 7 cm. At what distance from the ceiling is the image of the light bulb filament given by the mirror (point source)? Find the shape and size of the “bunny” obtained from a fragment of a mirror on the ceiling.
Questions:
1. Why does a beam of light become visible in smoke or fog?
2. A man standing on the shore of a lake sees an image of the Sun on the smooth surface of the water. How will this image move as the person moves away from the lake?
3. How far is it from you to the image of the Sun in a flat mirror?
4. Is twilight observed on the Moon?
5. If the surface of the water fluctuates, then the images of objects (the Moon and the Sun) in the water also fluctuate. Why?
6. How will the distance between an object and its image in a flat mirror change if the mirror is moved to the place where the image was?
7. Which is blacker: velvet or black silk? Three types of troops have black velvet shoulder straps: artillerymen (November 19, 1942), tankers (Stalingrad and Kursk), drivers (Ladoga).
8. Is it possible to measure the height of clouds using a powerful spotlight?
9. Why are snow and fog opaque, although the water is clear?
10. 
At what angle will the beam reflected from the plane mirror turn when the latter is rotated by 30 0?
11. How many images of the source S 0 can be seen in the system of flat mirrors M 1 and M 2? From what area will they be visible at the same time?
12. At what position of a flat mirror will a ball rolling straight along the surface of a table appear to be rising vertically upward in the mirror?
13. Malvina looks at her image in a small mirror, but she sees only part of her face. Will she see the whole face if she asks Pinocchio to move away with the mirror?
14. Does the mirror always “tell” the truth?
15. One day, flying over the mirror-like surface of a pond, Carlson noticed that his speed relative to the pond was exactly equal to his speed of removal from his image in the water. At what angle to the surface of the pond was Carlson flying?
16. Suggest a way to measure the height of an object if its base is accessible (inaccessible).
17. At what size of the mirror will the sunbeam have the shape of a mirror, and at what size will it have the shape of the disk of the Sun?
§§ 64-66. Ex. 33.34. Revision problems No. 64 and No. 65.
1. Make a model of a periscope.
2. A luminous point is located between two flat mirrors. How many images of a point can be obtained by placing the mirrors at an angle to each other.
3. Using a table lamp 1.5 - 2 m from the edge of the table and a wide-toothed comb, create a beam of parallel rays on the table surface. Place a mirror in their path and check the laws of light reflection.
4. If two rectangular flat mirrors forming a right angle are placed on a third mirror, then we obtain an optical system consisting of three mutually perpendicular mirrors - a “reflector”. What interesting property does it have?
5. Sometimes a sunbeam almost exactly repeats the shape of the mirror that is used to let it in, sometimes only approximately, and sometimes it is not at all similar in shape to the mirror. What does this depend on? At what size of the mirror will the sunbeam have the shape of a mirror, and at what size will it have the shape of the disk of the Sun?
“Since the renaissance of the sciences, since their very inception, no more wonderful discovery has been made than the discovery of the laws governing light ... when transparent bodies force it to change its path when they intersect.”
Maupertuis
Lesson 61/11. LIGHT REFRACTION
LESSON OBJECTIVE: Based on experiments, establish the law of light refraction and teach students to apply it when solving problems.
TYPE OF LESSON: Combined.
EQUIPMENT: Optical washer with accessories, LG-209 laser.
LESSON PLAN:
2. Survey 10 min
3. Explanation 20 min
4. Fixing 10 min.
5. Homework assignment 2-3 min
II. Fundamental survey:
1. The law of light reflection.
2. Constructing an image in a plane mirror.
Tasks:
1. It is required to illuminate the bottom of the well by directing the sun's rays at it. How should a flat mirror be positioned in relation to the Earth if the Sun's rays fall at an angle of 60° to the horizon?
2. The angle between the incident and reflected rays is 8 times greater than the angle between the incident ray and the mirror plane. Calculate the angle of incidence of the beam.
3. 
A long inclined mirror is in contact with the horizontal floor and inclined at an angle α to the vertical. A schoolboy approaches the mirror, whose eyes are located at a height h from the ground level. At what maximum distance from the bottom edge of the mirror will the student see: a) the image of his eyes; b) your full-length image?
4. Two plane mirrors form an angle α . Find the angle of deviation δ light beam. Angle of incidence of the beam on the mirror M 1 equals φ .
Questions:
1. At what angle of incidence of a beam on a flat mirror do the incident beam and the reflected beam coincide?
2. To see your full-length image in a flat mirror, its height must be at least half the height of a person. Prove it.
3. Why does a puddle on the road at night appear to the driver as a dark spot on a light background?
4. Is it possible to use a flat mirror instead of a white canvas (screen) in cinemas?
5. Why are shadows, even with one light source, never completely dark?
6. Why does the snow shine?
7. Why are figures drawn on foggy window glass clearly visible?
8. Why does a polished boot shine?
9. Two pins A and B are stuck in front of mirror M. Where on the dashed line should the observer’s eye be for the images of the pins to overlap each other?
10. There is a flat mirror hanging on the wall in the room. Experimenter Gluck sees a dimly lit object in it. Can Gluck illuminate this object by shining a flashlight on its imaginary image in the mirror?
11. Why does the chalkboard sometimes glow? Under what conditions will this phenomenon be observed?
12. Why are vertical light poles sometimes visible above the street lamps at night in winter?
III. Refraction of light at the interface between two transparent media. Demonstration of the phenomenon of light refraction. Incident ray and refracted ray, angle of incidence and angle of refraction.
Filling out the table:
Absolute refractive index of the medium ( n) is the refractive index of a given medium relative to vacuum. Physical meaning of the absolute refractive index: n = c/v.
Absolute refractive indices of some media: n air= 1,0003, = 1,33; n st= 1.5 (crown) - 1.9 (flint). A medium with a higher refractive index is called optically denser.
The relationship between the absolute refractive indices of two media and their relative refractive index: n 21 = n 2 / n 1.
Refraction is responsible for a number of optical illusions: the apparent depth of a body of water (explanation with a picture), a broken pencil in a glass of water (demonstration), short legs of a bather in the water, mirages (on asphalt).
Path of rays through a plane-parallel glass plate (demonstration).
IV. Tasks:
1. The beam passes from water to flint glass. The angle of incidence is 35°. Find the angle of refraction.
2. At what angle will the beam be deflected, falling at an angle of 45° on the surface of the glass (crown), on the surface of the diamond?
3. A diver, while underwater, determined that the direction to the Sun makes an angle of 45° with the vertical. Find the true position of the Sun relative to the vertical?
Questions:
1. Why does a lump of snow that falls into the water become invisible?
2. A man stands waist-deep in water on the horizontal bottom of a pool. Why does it seem to him that he is standing in a recess?
3. In the morning and early evening hours, the reflection of the Sun in calm water blinds the eyes, but at noon you can see it without squinting. Why?
4. In what material medium does light travel at the highest speed?
5. In what medium can light rays be curved?
6. If the surface of the water is not completely calm, then objects lying at the bottom seem to oscillate. Explain the phenomenon.
7. Why are the eyes of a person wearing dark glasses not visible, although the person himself sees quite well through such glasses?
§ 67. Ex. 36 Revision problems No. 56 and No. 57.
1. Using a table lamp 1.5 - 2 m away from the edge of the table and a wide-toothed comb, create a beam of parallel rays on the table surface. Having placed a glass of water and a triangular prism in their path, describe the phenomena and determine the refractive index of the glass.
2. If you place a coffee can on a white surface and quickly pour boiling water into it, you can see, looking from above, that the black outer wall has become shiny. Observe and explain the phenomenon
3. Try observing mirages using a hot iron.
4. Using a compass and ruler, construct the path of a refracted ray in a medium with a refractive index of 1.5 at a known angle of incidence.
5. Take a transparent saucer, fill it with water and place it on the page of an open book. Then, using a pipette, add milk to the saucer, stirring until you can no longer see the words on the page through the bottom of the saucer. If you now add granulated sugar to the solution, then at a certain concentration the solution will again become transparent. Why?
“Having discovered the refraction of light, it was natural to pose the question:
what is the relationship between the angles of incidence and refraction?
L. Cooper
Lesson FULL REFLECTION
LESSON OBJECTIVE: To introduce students to the phenomenon of total internal reflection and its practical applications.
TYPE OF LESSON: Combined.
EQUIPMENT: Optical washer with accessories, LG-209 laser with accessories.
LESSON PLAN:
1. Introductory part 1-2 min
2. Survey 10 min
3. Explanation 20 min
4. Fixing 10 min.
5. Homework assignment 2-3 min
II.Fundamental survey:
1. The law of light refraction.
Tasks:
1. A ray reflected from a glass surface with a refractive index of 1.7 forms a right angle with the refracted ray. Determine the angle of incidence and the angle of refraction.
2. Determine the speed of light in a liquid if, when a beam falls on the surface of a liquid from air at an angle of 45 0, the angle of refraction is 30 0.
3. A beam of parallel rays strikes the water surface at an angle of 30°. The width of the beam in air is 5 cm. Find the width of the beam in water.
4. A point source of light S is located at the bottom of a reservoir 60 cm deep. At a certain point on the surface of the water, the refracted ray released into the air turns out to be perpendicular to the ray reflected from the surface of the water. At what distance from the source S will the beam reflected from the surface of the water fall to the bottom of the reservoir? The refractive index of water is 4/3.
Questions:
1. Why do soil, paper, wood, sand appear darker if they are moistened with water?
2. Why, when sitting by the fire, do we see objects on the other side of the fire oscillating?
3. In what cases is the interface between two transparent media invisible?
4. Two observers simultaneously determine the height of the Sun above the horizon, but one is under water and the other is in the air. For which of them is the Sun higher above the horizon?
5. Why is the true length of the day somewhat longer than that given by astronomical calculations?
6. Construct the path of the ray through a plane-parallel plate if its refractive index is less than the refractive index of the surrounding medium.
III. The passage of a light beam from an optically less dense medium into an optically more dense medium: n 2 > n 1, sinα > sinγ.
The passage of a light beam from an optically denser medium to an optically less dense medium: n 1 > n 2, sinγ > sinα.
Conclusion: If a light beam passes from an optically more dense medium to an optically less dense medium, then it deviates from the perpendicular to the interface between the two media, reconstructed from the point of incidence of the beam. At a certain angle of incidence, called the limiting one, γ = 90° and light does not pass into the second medium: sinα prev = n 21.
Observation of total internal reflection. The limiting angle of total internal reflection when light passes from glass to air. Demonstration of total internal reflection at the glass-air interface and measurement of the limiting angle; comparison of theoretical and experimental results.
Change in the intensity of the reflected beam with a change in the angle of incidence. With total internal reflection, 100% of the light is reflected from the boundary (perfect mirror).
Examples of total internal reflection: a lantern at the bottom of a river, crystals, a reversible prism (demonstration), a light guide (demonstration), a luminous fountain, a rainbow.
Is it possible to tie a light beam in a knot? Demonstration with a polypropylene tube filled with water and a laser pointer. Use of total reflection in fiber optics. Transmitting information using a laser (10 6 times more information is transmitted than using radio waves).
The path of rays in a triangular prism: ; .
IV. Tasks:
1. Determine the limiting angle of total internal reflection for the transition of light from diamond to air.
2. A ray of light falls at an angle of 30 0 to the interface between two media and exits at an angle of 15 0 to this boundary. Determine the limiting angle of total internal reflection.
3. Light falls on an equilateral triangular prism made of crowns at an angle of 45° to one of the faces. Calculate the angle at which the light exits the opposite face. Refractive index crown 1.5.
4. A ray of light falls on one of the faces of an equilateral glass prism with a refractive index of 1.5, perpendicular to this face. Calculate the angle between this ray and the ray that left the prism.
Questions:
1. Why is it better to see fish swimming in the river from the bridge than from the low bank?
2. Why do the Sun and Moon appear oval at the horizon?
3. Why do gemstones sparkle?
4. Why, when you drive along a highway that is very hot from the sun, sometimes it seems like you see puddles on the road?
5. Why does a black plastic ball appear mirror-like in water?
6. The pearl fisher releases olive oil from his mouth at depth and the glare on the surface of the water disappears. Why?
7. Why is the hail formed in the lower part of the cloud dark, and the one formed in the upper part is light?
8. Why does a smoked glass plate in a glass of water appear mirror-like?
Abstract
- Propose a project for a solar concentrator (solar oven), which can be box-shaped, combined, parabolic, or with an umbrella-type mirror.
“In this world I know there is no count of treasures.”
L. Martynov
Lesson 62/12. LENS
LESSON OBJECTIVE: Introduce the concept of “lens”. Introduce students to different types of lenses; teach them how to construct an image of objects in a lens.
TYPE OF LESSON: Combined.
EQUIPMENT: Optical washer with accessories, set of lenses, candle, lenses on a stand, screen, filmstrip “Constructing an image in lenses.”
LESSON PLAN:
1. Introductory part 1-2 min
2. Survey 15 min
3. Explanation 20 min
4. Fastening 5 min.
5. Homework assignment 2-3 min
II.Fundamental survey:
1. Refraction of light.
2. Path of rays in a plane-parallel glass plate and a triangular prism.
Tasks:
1. What is the apparent depth of the river for a person looking at an object lying at the bottom, if the angle made by the line of sight with the perpendicular to the surface of the water is 70 0? Depth 2 m.
2. A pile is driven into the bottom of a reservoir 2 m deep, protruding 0.5 m from the water. Find the length of the shadow from the pile at the bottom of the reservoir at an angle of incidence of the rays of 30 0.
3. 
The beam falls on a plane-parallel glass plate 3 cm thick at an angle of 70°. Determine the displacement of the beam inside the plate.
4. A ray of light falls on a system of two wedges with a refractive angle of 0.02 rad and a refractive index of 1.4 and 1.7, respectively. Determine the beam deflection angle of such a system.
5. A thin wedge with an angle of 0.02 rad at the apex was made of glass with a refractive index of 1.5 and lowered into a pool of water. Find the angle of deflection of a beam propagating in water and passing through the wedge.
Questions:
1. Crushed glass is opaque, but if it is filled with water, it becomes transparent. Why?
2. Why does the virtual image of an object (for example, a pencil) under the same lighting in water appear less bright than in a mirror?
3. Why are the lambs on the crests of sea waves white?
4. Indicate the further path of the beam through a triangular glass prism.
5. What do you now know about light?
III. We will apply the basic laws of geometric optics to specific physical objects, obtain corollary formulas and, with their help, explain the principle of operation of various optical objects.
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A lens is a transparent body bounded by two spherical surfaces(drawing on the board). Demonstrations of lenses from the set. Fundamental points and lines: centers and radii of spherical surfaces, optical center, optical axis, principal optical axis, principal focus of a collecting lens, focal plane, focal length, lens power (demonstrations). Focus - from the Latin word focus - hearth, fire.
Converging lens ( F >0). Schematic representation of a converging lens in the figure. Constructing an image in a collecting lens of a point that does not lie on the main optical axis. Wonderful rays.
How to construct an image of a point in a converging lens if this point lies on the main optical axis?
Constructing an image of an object in a converging lens (extreme points).
The object is located behind the double focal length of the converging lens. Where and what kind of image of the object we will get (constructing an image of the object on the board). Can an image be captured on film? Yes! An actual image of the item.
Where and what image of an object will we get if the object is located at double the focal distance from the lens, between the focus and double focus, in the focal plane, between the focus and the lens.
Conclusion: A converging lens can provide:
a) a real image reduced, enlarged or equal to the object; an imaginary enlarged image of an object.
Schematic representation of diverging lenses in the figures ( F<0 ). Constructing an image of an object in a diverging lens. What image of an object do we get in a diverging lens?
Question: If your interlocutor wears glasses, then how can you determine which lenses these glasses have - converging or diverging?
Historical reference: A. Lavoisier's lens had a diameter of 120 cm and a thickness in the middle part of 16 cm, and was filled with 130 liters of alcohol. With its help it was possible to melt gold.
IV. Tasks:
1. Construct an image of an object AB in a converging lens ( Fig.1).
2. The figure shows the position of the main optical axis of the lens, the luminous point A and her image ( Rice. 2). Find the position of the lens and construct an image of the object BC.
3. The figure shows a converging lens, its main optical axis, a luminous point S and its image S "( Rice. 3). Determine the focal points of the lens by constructing them.
4. In Figure 4, the dashed line shows the main optical axis of the lens and the path of an arbitrary ray through it. By construction, find the main focal points of this lens.
Questions:
1. Is it possible to make a spotlight using a light bulb and a collecting lens?
2. Using the Sun as a light source, how can you determine the focal length of a lens?
3. A “convex lens” was glued together from two watch glasses. How will this lens act on a beam of rays in water?
4. Is it possible to light a fire at the North Pole with an ax?
5. Why does a lens have two focuses, but a spherical mirror only has one?
6. Will we see an image if we look through a converging lens at an object placed in its focal plane?
7. At what distance should a converging lens be placed from the screen so that its illumination does not change?
§§ 68-70 Ex. 37 - 39. Revision problems No. 68 and No. 69.
1. Fill an empty bottle halfway with the test liquid and, placing it horizontally, measure the focal length of this plane-convex lens. Using the appropriate formula, find the refractive index of the liquid.
“And the fiery flight of your spirit is content with images and likenesses.”
Goethe
Lesson 63/13. LENS FORMULA
LESSON OBJECTIVE: Derive the lens formula and teach students how to apply it when solving problems.
TYPE OF LESSON: Combined.
EQUIPMENT: A set of lenses and mirrors, a candle or light bulb, a white screen, a lens model.
LESSON PLAN:
1. Introductory part 1-2 min
2. Survey 10 min
3. Explanation 20 min
4. Fixing 10 min.
5. Homework assignment 2-3 min
II.Fundamental survey:
2. Constructing an image of an object in a lens.
Tasks:
1. The path of the beam through the diverging lens is given (Fig. 1). Find the focus by constructing.
2. Construct an image of an object AB in a converging lens (Fig. 2).
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3. Figure 3 shows the position of the main optical axis of the lens, source S and his image. Find the position of the lens and construct an image of the object AB.
4. Find the focal length of a biconvex lens with a radius of curvature of 30 cm, made of glass with a refractive index of 1.5. What is the optical power of the lens?
5. A ray of light falls on a diverging lens at an angle of 0.05 rad to the main optical axis and, having been refracted in it at a distance of 2 cm from the optical center of the lens, exits at the same angle relative to the main optical axis. Find the focal length of the lens.
Questions:
1. Can a plano-convex lens scatter parallel rays?
2. How will the focal length of the lens change if its temperature increases?
3. The thicker a lenticular lens is at the center compared to the edges, the shorter its focal length for a given diameter. Explain.
4. The edges of the lens were trimmed. Has its focal length changed (prove by construction)?
5. Construct the beam path behind the diverging lens ( Rice. 1)?
6. The point source is located on the main optical axis of the collecting lens. In what direction will the image of this source shift if the lens is rotated at a certain angle relative to an axis lying in the plane of the lens and passing through its optical center?
What can be determined using the lens formula? Experimental measurement of the focal length of a lens in centimeters (measurement d And f, calculation F).
Lens model and lens formula. Explore all cases with demonstrations using the lens formula and lens model. Result in the table:
| d | d = 2F | F< d < 2F | d = F | d< F | |
| f | 2F | f > 2F | f< 0 | ||
| image |
Г = 1/(d/F - 1). 1) d = F, Г→∞. 2) d = 2F, Г = 1. 3) d→∞, Г→0. 4) d = F, Г = - 2.
If the lens is diverging, then where should the crossbar be placed? What will be the image of the object in this lens?
Methods for measuring the focal length of a converging lens:
1. Obtaining an image of a distant object: , .
2. If the subject is in double focus d = 2F, That d = f, A F = d/2.
3. Using lens formula.
4. Using formula 
.
5. Using a flat mirror.
Practical applications of lenses: you can obtain an enlarged real image of an object (slide projector), a reduced real one and photograph it (camera), obtain an enlarged and reduced image (telescope and microscope), focus the sun's rays (solar station).
IV. Tasks:
1. Using a lens whose focal length is 20 cm, an image of an object is obtained on a screen located 1 m from the lens. At what distance from the lens is the object? What will the image be like?
2. The distance between the object and the screen is 120 cm. Where should a converging lens with a focal length of 25 cm be placed in order to obtain a clear image of the object on the screen?
§ 71 Task 16
1. Propose a project for measuring the focal length of spectacle lenses. Measure the focal length of the diverging lens.
2. Measure the diameter of the wire from which the spiral in the incandescent lamp is made (the lamp must remain intact).
3. A drop of water on the glass or a film of water tightening the wire loop acts as a lens. Make sure of this by looking at dots, small objects, and letters through them.
4. Using a converging lens and a ruler, measure the angular diameter of the Sun.
5. How should two lenses be positioned, one of which is converging and the other scattering, so that a beam of parallel rays, passing through both lenses, remains parallel?
6. Calculate the focal length of the laboratory lens, and then measure it experimentally.
"If a person examines letters or other small objects with a glass or other transparent body placed above the letters, and if this body is a spherical segment, ... the letters will appear larger."
Roger Bacon
Lesson 64/14. LABORATORY WORK No. 11: “MEASUREMENT OF THE FOCAL LENGTH AND OPTICAL POWER OF A CONVERSING LENS.”
LESSON OBJECTIVE: To teach students to measure the focal length and optical power of a converging lens.
TYPE OF LESSON: Laboratory work.
EQUIPMENT: Converging lens, screen, light bulb on a stand with a cap (candle), measuring tape (ruler), power supply, two wires.
WORK PLAN:
1. Introductory part 1-2 min
2. Brief instructions 5 min
3. Completion of work 30 minutes
4. Summing up 5 min
5. Homework assignment 2-3 min
II. The focal length of a converging lens can be measured in different ways:
1. Measure the distance from the object to the lens and from the lens to the image; using the lens formula, you can calculate the focal length: .
2. Having received an image of a remote light source () on the screen,
We directly measure the focal length of the lens ().
3. If an object is placed at double the focal length from the lens, then the image is also at double the focal length (having achieved equality d And f, directly measure the focal length of the lens).
4. Knowing the average focal length of the lens and the distance from the object to the lens ( d), it is necessary to calculate the distance from the lens to the image of the object ( f t) and compare it with that obtained experimentally ( f e).
III. Progress:
| No. | d, m | f, m | F, m | F avg, m | D, Wed | Character of the image | ||
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| 4. | f e | f t | ||||||
Additional task e: Measure the focal length of the diverging lens: D = D 1 + D 2.
Additional task: Measure the focal length of the lens using other methods.
IV. Summarizing.
V. Propose a project for a solar water heating installation with natural and forced circulation.
"Every consistently developing science grows only because
that human society needs it."
S.I. Vavilov
Lesson 65/15. PROJECTION DEVICE. CAMERA.
LESSON OBJECTIVE: To introduce students to some of the practical uses of lenses.
TYPE OF LESSON: Combined.
EQUIPMENT: Projector, camera.
LESSON PLAN:
1. Introductory part 1-2 min
2. Survey 10 min
3. Explanation 20 min
4. Fixing 10 min.
5. Homework assignment 2-3 min
II.Fundamental survey:
1. Lens formula.
2. Measuring the focal length of the lens.
Tasks:
1. At what distance from a lens with a focal length of 12 cm must an object be placed so that its actual image is three times larger than the object itself?
2. An object is located at a distance of 12 cm from a biconcave lens with a focal length of 10 cm. Determine at what distance from the lens the image of the object is? What will it be like?
Questions:
1. There are two identical spherical flasks and a table lamp. It is known that one flask contains water, the other contains alcohol. How to determine the contents of vessels without resorting to weighing?
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The diameter of the Sun is 400 times larger than the diameter of the Moon. Why are their apparent sizes almost the same?
3. The distance between the object and its image created by a thin lens is equal to 0.5F Where F- focal length of the lens. What image is this - real or imaginary?
4. Using a lens, an inverted image of a candle flame is obtained on the screen. Will the linear dimensions of this image change if part of the lens is obscured by a sheet of cardboard (prove by construction).
5. Determine by construction the position of the luminous point if two rays, after refraction in the lens, go as shown in Figure 1.
6. Subject given AB and his image. Determine the type of lens, find its main optical axis and the position of the foci ( Rice. 2).
7. A virtual image of the Sun was obtained in a flat mirror. Is it possible to burn through paper with this “imaginary Sun” using a collecting lens?
III. A projection device is a device designed to obtain a real and enlarged image of an object. Optical diagram of the projection apparatus on the board. At what distance from the objective lens should a translucent object be placed so that its actual image is many times larger than the object itself? How is it necessary to change the distance from the object to the objective lens if the distance from the projection apparatus to the screen increases or decreases?
Lesson objectives:
– students should know the concept of a mirror;
– students must know the properties of the image in a plane mirror;
– students must be able to construct an image in a flat mirror;
– continue work on the formation of methodological knowledge and skills, knowledge about the methods of natural science and be able to apply them;
– continue work on developing experimental research skills when working with physical instruments;
– continue work on developing students’ logical thinking and developing the ability to build inductive conclusions.
Organizational forms and methods of teaching: conversation, test, individual survey, research method, experimental work in pairs.
Teaching aids: Mirror, ruler, eraser, periscope, multimedia projector, computer, presentation (See. Annex 1).
Lesson plan:
- Checking d/z (test).
- Updating knowledge. Setting the topic, goals, and objectives of the lesson together with the students.
- Learning new material as students work with equipment.
- Generalization of experimental results and formulation of properties.
- Practicing practical skills in constructing an image in a flat mirror.
- Summing up the lesson.
During the classes
1. Checking the d/z (test).
(The teacher distributes test cards.)
Test: Law of Reflection
- The angle of incidence of a light ray on a mirror surface is 15 0 . What is the angle of reflection?
A 30 0
B 40 0
At 15 0 - The angle between the incident and reflected rays is 20 0. What will be the angle of reflection if the angle of incidence increases by 5 0?
A 40 0
B 15 0
At 30 0
Answers for the test.
Teacher: Exchange your work and check the correctness of your work by checking your answers against the standard. Give marks based on the grading criteria (answers are written on the back of the board).
Assessment criteria for the test:
for a rating of “5” – all;
for a grade of “4” – task No. 2;
for a grade of “3” – task No. 1.
Teacher: You were given home task No. 4 Exercise 30 (textbook by Peryshkin A.V.) of a research nature. Who completed this task? ( The student works at the board, offering his version.)
Problem text: The height of the Sun is such that its rays make an angle of 40 0 with the horizon. make a drawing (Fig. 131) and show on it how the mirror AB needs to be positioned so that the “bunny” gets to the bottom of the well.
2. Updating knowledge. Setting the topic, goals, and objectives of the lesson together with the students.
Teacher: Now let's remember the basic concepts learned in previous lessons and decide on the topic of today's lesson.
Because the keyword is encrypted in the crossword.
Teacher: What keyword did you get? MIRROR.
What do you think is the topic of today's lesson?
Yes, topic of the lesson: Mirror. Constructing an image in a plane mirror.
Open your notebooks, write down the date and topic of the lesson.
Application.Slide 1.
Teacher: What questions would you like answered today, given the topic of the lesson?
(Children ask questions. The teacher summarizes, thus setting the goals of the lesson.)
Teacher:
- Explore the concept of “mirror”. Identify types of mirrors.
- Find out what properties it has.
- Learn to build an image in a mirror.
3. Learning new material as students work with equipment.
Student activity: listen and remember the material.
Teacher: Let's start studying new material, it should be said that mirrors are as follows:
Teacher: Today we will study a plane mirror in more detail.
Teacher: A flat mirror (or just a mirror) called a flat surface that specularly reflects light
Teacher:Write down the diagram and definition of a mirror in your notebook.
Student activity: make notes in a notebook.
Teacher: Consider the image of an object in a plane mirror.
You all know very well that the image of an object in a mirror is formed behind the mirror, where it actually does not exist.
How does this work? ( The teacher presents the theory and the students take an active part.)
Slide 5 . (Experimental activities of students .)
Experiment 1. You have a small mirror on your table. Install it in a vertical position. Place the eraser in a vertical position in front of the mirror at a short distance. Now take a ruler and place it so that the zero is near the mirror.
Exercise. Read the questions on the slide and answer them. (Part A questions)
Students formulate a conclusion: the virtual image of an object in a plane mirror is at the same distance from the mirror as the object in front of the mirror
Slide 6. (Experimental activities of students . )
Experiment 2. Now take a ruler and place it vertically along the eraser.
Exercise. Read the questions on the slide and answer them. (Part B questions)
Students formulate a conclusion: the dimensions of the image of an object in a plane mirror are equal to the dimensions of the object.
Assignments for experiments.
Slide 7. (Experimental activities of students.)
Experiment 3. Draw a line on the eraser on the right and place it again in front of the mirror. The ruler can be removed.
Exercise. What did you see?
Students formulate a conclusion: the object and its images are symmetrical figures, but not identical
4. Generalization of experimental results and formulation of properties.
Teacher: SO, these conclusions can be called properties of flat mirrors, let's list them again and write them down in a notebook.
Slide 8 . (Students write down the properties of mirrors in their notebooks.)
- The virtual image of an object in a plane mirror is at the same distance from the mirror as the object in front of the mirror.
- The dimensions of the image of an object in a flat mirror are equal to the dimensions of the object.
- The object and its images are symmetrical figures, but not identical.
Teacher:Attention to the slide. We solve the following problems (the teacher asks several children for the answer, and then one student outlines the course of his reasoning, based on the properties of mirrors).
Student activities: Active participation in problem analysis discussions.
1) A person stands at a distance of 2 m from a plane mirror. At what distance from the mirror does he see his image?
A 2m
B 1m
At 4m
2) A person stands at a distance of 1.5 m from a flat mirror. At what distance from himself does he see his image?
A 1.5m
B 3m
At 1m
5. Practicing practical skills in constructing an image in a flat mirror.
Teacher: So, we have learned what a mirror is, established its properties, and now we must learn to build an image in the mirror, taking into account the above properties. We work together with me in our notebooks. ( The teacher works on the blackboard, students in a notebook.)
| Rules for constructing an image | Example |
|
So, the image should be the same size as the object, located behind the mirror at the same distance as the object in front of the mirror. |
6. Summing up the lesson.
Teacher: Application of mirror:
- in everyday life (several times a day we check whether we look good);
- in cars (rear view mirrors);
- in the attractions (laugh room);
- in medicine (in particular in dentistry) and in many other fields, the periscope is of particular interest;
- periscope (used for observation from a submarine or from trenches), demonstration of the device, including homemade ones.
Teacher: Let's remember what we learned in class today?
What is a mirror?
What properties does it have?
How to construct an image of an object in a mirror?
What properties do we take into account when constructing an image of an object in a mirror?
What is a periscope?
Student activity: answer the questions posed.
Homework: §64 (textbook A.V. Peryshkin, 8th grade), notes in the notebook to make a periscope as desired No. 1543, 1549, 1551,1554 (problem book V.I. Lukashik).
Teacher: Continue the sentence...
Reflection:
Today in class I learned...
I enjoyed my lesson today...
I didn't like my lesson today...
Giving marks for the lesson (students give them, explaining why they give this particular mark).
Used Books:
- Gromov S.V. Physics: Textbook for general education textbook institutions/ S. V. Gromov, N. A. Rodina. – M.: Education, 2003.
- Zubov V. G., Shalnov V. P. Problems in physics: A manual for self-education: Study guide. – M.: Nauka. Main editorial office of physical and mathematical literature, 1985.
- Kamenetsky S. E., Orekhov V. P. Methods for solving problems in physics in secondary school: Book. for the teacher. – M.: Education, 1987.
- Koltun M. World of physics. Publishing house “Children's Literature”, 1984.
- Maron A. E. Physics. 8th grade: Educational manual / A. E. Maron, E. A. Maron. M.: Bustard, 2004.
- Methods of teaching physics in grades 6–7 of secondary school. Ed. V. P. Orekhov and A. V. Usova. M., “Enlightenment”, 1976.
- Peryshkin A.V. Physics. 8th grade: Textbook. for general education textbook establishments. – M.: Bustard, 2007.
If the reflective surface of the mirror is flat, then it is a type of flat mirror. Light is always reflected from a flat mirror without scattering according to the laws of geometric optics:
- The angle of incidence is equal to the angle of reflection.
- The incident ray, the reflected ray, and the normal to the mirror surface at the point of incidence lie in the same plane.
One thing to remember is that a glass mirror has a reflective surface (usually a thin layer of aluminum or silver) placed on its back. It is covered with a protective layer. This means that although the main reflected image is formed on this surface, light will also be reflected from the front surface of the glass. A secondary image is formed, which is much weaker than the main one. It is generally invisible in everyday life, but poses serious problems in the field of astronomy. For this reason, all astronomical mirrors have a reflective surface applied to the front side of the glass.
Image Types
There are two types of images: real and imaginary.
The real is formed on the film of a video camera, camera or on the retina of the eye. Light rays pass through a lens or lens, converge when falling on a surface, and at their intersection form an image.
Imaginary (virtual) is obtained when rays, reflected from a surface, form a divergent system. If you complete the continuation of the rays in the opposite direction, then they will certainly intersect at a certain (imaginary) point. It is from these points that a virtual image is formed, which cannot be recorded without the use of a flat mirror or other optical instruments (magnifying glass, microscope or binoculars).
Image in a plane mirror: properties and construction algorithm
For a real object, the image obtained using a plane mirror is:
- imaginary;
- straight (not inverted);
- the dimensions of the image are equal to the dimensions of the object;
- the image is at the same distance behind the mirror as the object in front of it.
Let's construct an image of some object in a plane mirror.
Let's use the properties of a virtual image in a plane mirror. Let's draw an image of a red arrow on the other side of the mirror. Distance A is equal to distance B, and the image is the same size as the object.
A virtual image is obtained at the intersection of the continuation of reflected rays. Let's depict light rays coming from an imaginary red arrow to the eye. Let us show that the rays are imaginary by drawing them with a dotted line. Continuous lines coming from the surface of the mirror show the path of the reflected rays.
Let's draw straight lines from the object to the points of reflection of the rays on the surface of the mirror. We take into account that the angle of incidence is equal to the angle of reflection.
Plane mirrors are used in many optical instruments. For example, in a periscope, flat telescope, graphic projector, sextant and kaleidoscope. A dental mirror for examining the oral cavity is also flat.
Reflection of light- this is a phenomenon in which the incidence of light on the interface between two media MN part of the incident light flux, having changed the direction of its propagation, remains in the same medium. Incident beamA.O.– a ray showing the direction of light propagation. Reflected beamO.B.- a ray showing the direction of propagation of the reflected part of the light flux.
Angle of incidence– the angle between the incident beam and the perpendicular to the reflecting surface.
Reflection angle 
- the angle between the reflected beam and the perpendicular to the interface at the point of incidence of the beam.
The law of light reflection: 1) the incident and reflected rays lie in the same plane with the perpendicular established at the point of incidence of the ray to the interface between the two media; 2) the angle of reflection is equal to the angle of incidence.
A mirror whose surface is a plane is called a plane mirror. Mirror reflection- This is a directional reflection of light.
If the interface between media is a surface whose uneven dimensions are greater than the wavelength of light incident on it, then mutually parallel light rays incident on such a surface do not retain their parallelism after reflection, but are scattered in all possible directions. This reflection of light is called absent-minded or diffuse.
Real Image- this is the image that is obtained when the rays intersect.
Virtual image- this is the image that is obtained by continuing the rays.
Construction of images in spherical mirrors.
Spherical mirror MK called the surface of a spherical segment that specularly reflects light. If light is reflected from the inner surface of a segment, then the mirror is called concave, and if from the outer surface of the segment – convex. A concave mirror is collecting and convex - scattering.
Center of the sphere C, from which a spherical segment is cut to form a mirror is called optical center of the mirror, and the vertex of the spherical segment O- his pole; R – radius of curvature of a spherical mirror.
Any straight line passing through the optical center of a mirror is called optical axis(KC; M.C.). The optical axis passing through the pole of the mirror is called main optical axis (O.C.). Rays coming near the main optical axis are called paraxial.
Full stop F, in which paraxial rays intersect after reflection and incident on a spherical mirror parallel to the main optical axis are called main focus.
The distance from the pole to the main focus of a spherical mirror is called focalOF.
Any ray incident along one of its optical axes is reflected from the mirror along the same axis.
Formula for a concave spherical mirror:
, Where d– distance from the object to the mirror (m), f– distance from the mirror to the image (m).
Formula for the focal length of a spherical mirror:
or 
The quantity D, the reciprocal of the focal length F of a spherical mirror, is called optical power.
/diopter/.
The optical power of a concave mirror is positive, while that of a convex mirror is negative.
The linear magnification Γ of a spherical mirror is the ratio of the size of the image H it creates to the size of the imaged object h, i.e. 
.
