Sections: Physics
The purpose of the lesson:
- Ensure the process of mastering the basic concepts of the topic “lens” and the principle of constructing images produced by a lens
- To promote the development of students' cognitive interest in the subject
- Contribute to the development of accuracy during the execution of drawings
Equipment:
- Rebuses
- Converging and diverging lenses
- Screens
- Candles
- Crossword
What lesson did we come to? (rebus 1) physics
Today we will study a new section of physics - optics. You were introduced to this section back in 8th grade and probably remember some aspects of the topic “Light Phenomena”. In particular, let's remember the images provided by mirrors. But first:
- What types of images do you know? (imaginary and real).
- What image does the mirror give? (Imaginary, direct)
- How far is it from the mirror? (on the same as the item)
- Do mirrors always tell us the truth? (message “On the contrary once again”)
- Is it always possible to see yourself in the mirror as you are, even if it’s the other way around? (message “Mirrors-teasing”)
Today we will continue our lecture and talk about another subject of optics. Guess. (rebus 2) lens
Lens– a transparent body bounded by two spherical surfaces.
Thin Lens– its thickness is small compared to the radii of curvature of the surface.
Main elements of the lens:
Distinguish a converging lens from a diverging lens by touch. The lenses are on your table.
How to construct an image in a converging and diverging lens?
1. Subject behind double focus.
2. Subject in double focus
3. Subject between focus and double focus
4. Subject in focus
5. Object between focus and lens
6. Diverging lens
Thin lens formula =+
How long ago did people learn to use lenses? (message “In the world of the invisible”)
And now we will try to get an image of a window (candle) using the lenses you have on your table. (Experiments)
Why do we need lenses? (for glasses, treatment of myopia, farsightedness) - This is your first homework - to prepare a report on correcting myopia and farsightedness with the help of glasses.
So, what phenomenon did we use to teach today's lesson? (rebus 3) observation.
Now we’ll check how you learned the topic of today’s lesson. To do this, let's solve a crossword puzzle.
Homework:
- puzzles,
- Crosswords,
- reports of myopia and farsightedness,
- lecture material
Teasing mirrors
So far we have been talking about honest mirrors. They showed the world as it is. Well, maybe turned from right to left. But there are teasing mirrors, distorting mirrors. Many culture and recreation parks have such an attraction - a “laugh room”. There, everyone can see themselves either short and round, like a head of cabbage, or long and thin, like a carrot, or like a sprouted onion: almost without legs and with a swollen belly, from which, like an arrow, a narrow chest stretches upward and an ugly elongated head on the thinnest neck.
The kids are dying of laughter, and the adults, trying to remain serious, just shake their heads. And because of this, the reflections of their heads in the teasing mirrors become distorted in the most hilarious way.
There is not a laughter room everywhere, but teasing mirrors surround us in life. You've probably admired your reflection in a glass ball from the New Year's tree more than once. Or in a nickel-plated metal teapot, coffee pot, samovar. All the images are very funny distorted. This is because the “mirrors” are convex. Convex mirrors are also attached to the handlebars of a bicycle, motorcycle, and near the driver's cab of a bus. They provide an almost undistorted, but somewhat reduced image of the road behind, and on buses also the back door. Direct mirrors are not suitable here: too little is visible in them. And a convex mirror, even a small one, contains a large picture.
There are sometimes concave mirrors. They are used for shaving. If you come close to such a mirror, you will see your face greatly magnified. The spotlight also uses a concave mirror. It is this that collects the rays from the lamp into a parallel beam.
In a world of the unknown
About four hundred years ago, skilled craftsmen in Italy and Holland learned to make glasses. Following glasses, magnifying glasses were invented for viewing small objects. It was very interesting and exciting: to suddenly see in all the details some millet grain or a fly leg!
In our age, radio amateurs are building equipment that allows them to receive increasingly distant stations. And three hundred years ago, optics enthusiasts were keen on grinding ever stronger lenses, allowing them to penetrate further into the world of the invisible.
One of these amateurs was the Dutchman Anthony Van Leeuwenhoek. The lenses of the best masters of that time were magnified by only 30-40 times. And Leeuwenhoek's lenses gave an accurate, clear image, magnified 300 times!
It was as if a whole world of wonders was opening up before the inquisitive Dutchman. Leeuwenhoek dragged everything that caught his eye under glass.
He was the first to see microorganisms in a drop of water, capillary vessels in the tail of a tadpole, red blood cells and dozens, hundreds of other amazing things that no one had suspected before.
But think that Leeuwenhoek found his discoveries easy. He was a selfless person who devoted his entire life to research. His lenses were very uncomfortable, not like today's microscopes. I had to rest my nose on a special stand so that my head would be completely motionless during observation. And just like that, leaning against the stand, Leeuwenhoek did his experiments for 60 years!
Once again it's the other way around
In the mirror you don’t see yourself exactly the way those around you see you. In fact, if you comb your hair to one side, in the mirror it will be combed to the other. If there are moles on the face, they will also appear on the wrong side. If you turn all this over in a mirror, the face will seem different, unfamiliar.
How can you still see yourself the way others see you? The mirror turns everything upside down... Well then! Let's outsmart him. Let's slip him an image, already inverted, already mirrored. Let him turn it the other way around again, and everything will fall into place.
How to do it? Yes, with the help of a second mirror! Stand in front of a wall mirror and take another, manual one. Hold it at an acute angle to the wall. You will outwit both mirrors: your “right” image will appear in both. This is easy to check using the font. Bring a book with a large inscription on the cover to your face. In both mirrors the inscription will be read correctly, from left to right.
Now try to pull your forelock. I am sure that this will not be possible right away. This time the image in the mirror is completely correct, not turned from right to left. This is why you will make mistakes. You are used to seeing a mirror image in the mirror.
In ready-made dress stores and tailoring studios there are three-leaf mirrors, the so-called trellises. You can also see yourself “from the outside” in them.
Literature:
- L. Galpershtein, Fun Physics, M.: Children's Literature, 1994
The lens represents a body, transparent and limited. The limiters of the lens body are most often either two curved surfaces, or one curved and the other flat. As you know, lenses can be convex or concave. Accordingly, a lens whose middle plane is thickened relative to its edges is convex. Concave lenses present a different picture: their middle is thinner relative to the edge surface. If the refractive index of the rays of the environment is less than the same index of a convex lens, then in it the beam formed by parallel rays is refracted and transformed into a converging beam. Concave lenses with such properties are called converging lenses. If in a concave lens a beam of parallel directed rays turns into divergent upon refraction, then these are divergent concave lenses; in them, air acts as the external medium.
The lens is a spherical surface with geometric centers. The straight line that connects the centers is the main optical axis. Thin lenses have a thickness less than their radius of curvature. For such lenses, it is true that their segment vertices are closely spaced and represent an optical center. In this case, a secondary axis is any straight line passing through the center at an angle to the straight line connecting the centers of the spherical surfaces. But to determine the main focus of a lens, it is enough to imagine that a beam of rays hits a collecting concave lens. Moreover, these rays are parallel to the main axis. After refraction, such rays will gather at one point, which will be the focus. In focus you can see the continuation of the rays. These are rays directed parallel to the main axis before refraction. But this trick is imaginary. There is also a main focus of the diverging lens. Or rather, two main focuses. If you imagine the main optical axis, then the main foci will be on it at an equal distance from the center. If we calculate the reciprocal of the focal length, we get the optical power.
The unit of optical power of a lens is the diopter, if we mean the SI system. Typically, for a converging lens, its optical power is positive, while for a diverging lens it will be negative. If the plane has the property of passing through the main focus of the lens and at the same time perpendicular to the main axis, then it is the focal plane. It is reliably known that rays in the form of a beam directed at the lens and at the same time being parallel to the secondary optical axis will be collected at the intersection of the axis and the focal plane. The ability of lenses to reflect and refract is used in optical instrumentation.
We all know examples of everyday use of lenses: a magnifying glass, glasses, a camera, in science and research it is a microscope. The significance of the discovery of the properties of lenses for humans is enormous. In optics, spherical lenses are most often used. They are made of glass and limited to spheres.
Types of lenses Thin - the thickness of the lens is small compared to the radii of the lens surfaces and the distance of the object from the lens. Thin lens formula 1 1 + 1 = F d f . F= d f ; d+ f where F – focal length; d is the distance from the object to the lens; f – distance from the lens to the image optical center R 1 О О 1 main optical axis R 2 О 2
Characteristics of lenses 1. Focal length The point at which the rays intersect after refraction in the lens is called the main focus of the lens (F). F
Characteristics of lenses 1. Focal length A converging lens has two main actual foci. F Focal length (F)
Characteristics of lenses 2. Optical power of a lens The reciprocal of the focal length is called the optical power of the lens D = 1/F Measured in diopters (dopters) 1 diopter = 1/m The optical power of a converging lens is considered a positive value, and a diverging lens is considered a negative value.
Protecting your vision You must: You must not: • look at an object; read while eating, by candlelight, in a moving vehicle and lying down; a distance of at least 30 cm, sit at the computer at a distance of 6070 cm from the screen, from the TV - 3 m (the screen should be at eye level); Ш so that the light falls from the left side; Ш skillfully use household appliances; Ш types of work that are dangerous to the eyes should be performed with special glasses; § watch TV continuously for more than 2 hours; § so that the room lighting is too bright; § openly look at direct rays of sunlight; § Rub your eyes with your hands if you get dust. If a foreign body gets into your eye, wipe your eye with a clean, damp cloth. If you notice problems with your vision, consult a doctor (ophthalmologist).
Completed by: teacher of Kuznetsk secondary school Pryakhina N.V.
Lesson Plan
Lesson stages, content | Form | Teacher activities | Student activities |
1. Review homework 5 min |
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2.1. Introduction to the concept of lens | Thought experiment | Conducts a thought experiment, explains, demonstrates a model, draws on the board | Conduct a thought experiment, listen, ask questions |
2.2. Identification of features and properties of a lens | Raises problematic questions and gives examples | ||
2.3. Explanation of the path of rays in a lens | Raises problematic questions, draws, explains | Answer questions and draw conclusions |
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2.4. Introduction of the concept of focus, optical power of a lens | Asks leading questions, draws on the board, explains, shows | Answer questions, draw conclusions, work with a notebook |
2.5. Image construction | Explanation | Tells, demonstrates model, shows banners | answer questions, draw in a notebook |
3. Consolidation of new material 8 min |
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3.1. The principle of image construction in lenses | Raises problematic questions | Answer questions and draw conclusions |
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3.2. Test solution | Work in pairs | Correction, individual assistance, control | Answer test questions and help each other |
4.Homework 1 min |
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§63.64, ex.9 (8) Be able to compose a story from an outline. |
Lesson. Lens. Constructing an image in a thin lens.
Target: Provide knowledge about lenses, their physical properties and characteristics. To develop practical skills in applying knowledge about the properties of lenses to find an image using the graphical method.
Tasks: study the types of lenses, introduce the concept of a thin lens as a model; introduce the main characteristics of the lens - optical center, main optical axis, focus, optical power; develop the ability to construct the path of rays in lenses.
Use problem solving to continue building calculation skills.
Lesson structure: educational lecture (mostly the teacher presents new material, but students take notes and answer the teacher’s questions as the material is presented).
Interdisciplinary connections: drawing (constructing rays), mathematics (calculations using formulas, using microcalculators to reduce time spent on calculations), social science (the concept of the laws of nature).
Educational equipment: photographs and illustrations of physical objects from the multimedia disk “Multimedia Library for Physics”.
Lesson summary.
In order to repeat what has been learned, as well as check the depth of knowledge assimilation by students, a frontal survey is conducted on the topic studied:
What phenomenon is called refraction of light? What is its essence?
What observations and experiments suggest a change in the direction of propagation of light when it passes into another medium?
Which angle - incidence or refraction - will be greater if a ray of light passes from air to glass?
Why, while in a boat, is it difficult to hit a fish swimming nearby with a spear?
Why is the image of an object in water always less bright than the object itself?
In what case is the angle of refraction equal to the angle of incidence?
2. Learning new material:
A lens is an optically transparent body bounded by spherical surfaces.�
Convex lenses are: biconvex (1), plano-convex (2), concave-convex (3).
Concave lenses are: biconcave (4), plano-concave (5), convex-concave (6).
In the school course we will study thin lenses.
A lens whose thickness is much less than the radii of curvature of its surfaces is called a thin lens.
Lenses that convert a beam of parallel rays into a converging one and collect it at one point are called collecting lenses.
Lenses that convert a beam of parallel rays into a divergent one are called scattering lenses.�The point at which the rays are collected after refraction is called focus. For a converging lens – valid. For scattering - imaginary.
Let us consider the path of light beams through a diverging lens:
We enter and display the main parameters of the lenses:
Optical center of the lens;
Optical axes of the lens and the main optical axis of the lens;
The main focal points of the lens and the focal plane.
Constructing images in lenses:
A point object and its image always lie on the same optical axis.
A ray incident on a lens parallel to the optical axis, after refraction through the lens, passes through the focus corresponding to this axis.
A ray passing through the focus before the collecting lens, after the lens, propagates parallel to the axis corresponding to this focus.
A ray parallel to the optical axis intersects it after refraction in the focal plane.
d – distance of object to lens
F – focal length of the lens.
1. The object is behind the double focal length of the lens: d > 2F.
The lens will give a reduced, inverted, real image of the object.
The object is between the focus of the lens and its double focus: F< d < 2F
The lens gives a magnified, inverted, real image of the object.�
An object is placed at the focus of the lens: d = F
The image of the item will be blurred.
4. The object is between the lens and its focus: d< F
the image of the object is enlarged, virtual, direct and located on the same side of the lens as the object.
5. Images produced by a diverging lens.
the lens does not produce actual images lying on the same side of the lens as the object.
Thin lens formula:
Formula for finding the optical power of a lens:
the reciprocal of the focal length is called the optical power of the lens. The shorter the focal length, the greater the optical power of the lens.
Optical instruments:
camera
Cinema camera
Microscope
Test.
What lenses are shown in the pictures?
What device can be used to obtain the image shown in the figure.
A. camera b. movie camera in. magnifying glass
Which lens is shown in the picture?
A. collecting
b. scattering
concave
Educational: to form concepts about lenses, types of lenses and their main characteristics; to form practical skills to apply knowledge about the properties of lenses to find images using the graphical method. Developmental: to develop the ability to operate with judgments; develop students’ speech through the organization of dialogic communication in the classroom; involve children in solving educational problem situations to develop their logical thinking; maintain students' attention through changing educational activities. Educational: cultivate cognitive interest, interest in the subject. Lesson Objectives
A lens is a transparent body bounded by two curved (usually spherical) or curved and flat surfaces. A lens is a transparent body bounded by two curved (usually spherical) or curved and flat surfaces. Lens The first mention of lenses can be found in the ancient Greek play "Clouds" by Aristophanes (424 BC), where fire was made using convex glass and sunlight. Lens (German Linse, from Latin lens - lentil) - a disk of transparent homogeneous material, bounded by two polished surfaces - spherical or spherical and flat.. Lens
The eye is the organ of vision. A person sees not with his eyes, but through his eyes, from where information is transmitted through the optic nerve to certain areas of the brain, where the picture of the external world that we see is formed. All these organs make up our visual analyzer, or visual system.
If a beam of rays parallel to the main optical axis falls on a collecting lens, then after refraction in the lens they are collected at one point F, which is called the main focus of the lens. At the focus of the diverging lens, the extensions of the rays intersect, which before refraction were parallel to its main optical axis. The focus of a diverging lens is imaginary. There are two main focuses; they are located on the main optical axis at the same distance from the optical center of the lens on opposite sides of it. Lens focus lens focus (F) optical center of the lens main optical axis of the lens
The dimensions and location of the image of an object in a converging lens depend on the position of the object relative to the lens. Depending on the distance from the lens the object is located, you can get either an enlarged image (F 2F). or reduced (d > 2F). Conclusion 2F). or reduced (d > 2F). Conclusion"> 
0 for converging lenses. D 0 for converging lenses. D 24 Lens optical power diopter D > 0 for converging lenses. D 0 for converging lenses. D 0 for converging lenses. D 0 for converging lenses. D 0 for converging lenses. D title=" Lens power diopter D > 0 for converging lenses. D
Visual hygiene 1. Read only in good lighting. 2. In daylight, the desktop should be positioned so that the window is on the left. 3. In artificial lighting, the table lamp must be on the left and must be covered with a lampshade. 4. You should not watch TV for too long. 5. After every minute of working on the computer, a pause is necessary.
Vision and proper nutrition Proper nutrition, including a sufficient amount of vitamins, especially D and A, is of great importance for good vision. Vitamin D is found in foods such as beef and pork liver, herring, egg yolk, and butter. The richest foods in vitamin A are cod liver, beef and pork liver, chicken egg yolk, cream, and butter. Carotene, a substance from which the human body synthesizes vitamin A, is found in large quantities in carrots, sweet peppers, sea buckthorn, rose hips, green onions, parsley, sorrel, apricots, spinach, and lettuce.
1. Why can’t you water the flowers in the garden on a sunny summer day? 2. By gluing two convex watch glasses together, you can get an air convex lens. If such a lens is placed in water, will it be a converging lens? 3. Compare the two pictures. What common? What is the difference? Think and answer
Using a lens, an inverted image of a candle flame is obtained on the screen. How will the size of the image change if part of the lens is obscured by a sheet of paper? 1. Part of the image will disappear. 2. The image dimensions will not change. 3. The sizes will increase. 4. The sizes will decrease. Question 2
Application of lenses Application of lenses Lenses are a universal optical element of most optical systems. Lenses are a universal optical element of most optical systems. Biconvex lenses are used in most optical instruments, the same lens is the lens of the eye. Meniscus lenses are widely used in glasses and contact lenses. Biconvex lenses are used in most optical instruments, the same lens is the lens of the eye. Meniscus lenses are widely used in glasses and contact lenses. In a converging beam behind a collecting lens, light energy is concentrated at the focus of the lens. Burning with a magnifying glass is based on this principle.
Reflection (check your answer in the table) Judgments YesNo I don’t know During the lesson I: 1) learned a lot of new things; 2) showed his knowledge; 3) communicated with interest with the teacher and classmates. During the lesson I felt: 1) free; 2) constrained; 3) cozy. During the lesson I liked: 1) collective solution of cognitive problems and questions; 2) visibility; 3) other (specify).
Thanks for your attention, thanks for the lesson! Homework § (Gendenshtein L.E.. Physics. 8th grade. - M.: Mnemosyne, 2009). (Gendenstein L.E.. Physics. 8th grade. - M.: Mnemosyne, 2009).
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