Lesson objectives:

– students should know the concept of a mirror;
– students should know the properties of the image in flat 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 development work logical thinking students, to develop 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:

1. Checking d/z (test).
2. Updating knowledge. Setting the topic, goals, and objectives of the lesson together with the students.
3. Learning new material as students work with equipment.
4. Generalization of experimental results and formulation of properties.
5. Practicing practical skills in constructing an image in a flat mirror.
6. Summing up the lesson.

During the classes

1. Checking the d/z (test).

(The teacher distributes test cards.)

Test: Law of Reflection

1. 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
2. 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 your grades, taking into account the evaluation criteria (answers are recorded on back side boards).

Test scoring criteria:

for a rating of “5” – everything;
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 encrypted in the crossword puzzle.

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:

1. Explore the concept of “mirror”. Identify types of mirrors.
2. Find out what properties it has.
3. 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 on your table small mirror. 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

We apply a ruler to the mirror so that one side of the right angle lies along the mirror. We move the ruler so that the point we want to construct lies on the other side right angle We draw a line from point A to the mirror and extend it beyond the mirror to the same distance and get point A 1. We do everything similarly for point B and get point B 1 We connect point A 1 and point B 1, we get an image A 1 B 1 of the object AB.

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:

1. Gromov S.V. Physics: Textbook for general education textbook institutions/ S. V. Gromov, N. A. Rodina. – M.: Education, 2003.
2. 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.
3. Kamenetsky S. E., Orekhov V. P. Methods for solving problems in physics in secondary school: Book. for the teacher. – M.: Education, 1987.
4. Koltun M. World of physics. Publishing house “Children's Literature”, 1984.
5. Maron A. E. Physics. 8th grade: Educational and methodological manual/ A. E. Maron, E. A. Maron. M.: Bustard, 2004.
6. Methods of teaching physics in grades 6–7 high school. Ed. V. P. Orekhov and A. V. Usova. M., “Enlightenment”, 1976.
7. Peryshkin A.V. Physics. 8th grade: Textbook. for general education textbook establishments. – M.: Bustard, 2007.

>>Physics: Constructing an image in a mirror

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Construction of images in mirrors and their characteristics.

An image of any point A of an object in a spherical mirror can be constructed using any pair of standard rays: To construct an image of any point A of an object, it is necessary to find the point of intersection of any two reflected rays or their extensions; the most convenient are rays going as shown in the figures 2.6 – 2.9

2) a ray passing through the focus, after reflection, will go parallel to the optical axis on which this focus lies;

4) the beam incident on the pole of the mirror, after reflection from the mirror, goes symmetrically to the main optical axis (AB=BM)

Let's look at a few examples of constructing images in concave mirrors:

2) The object is located at a distance that is equal to the radius of curvature of the mirror. The image is real, equal in size to the size of the object, inverted, located strictly under the object (Fig. 2.11).

Rice. 2.12

3) The object is located between the focus and the pole of the mirror. Image – virtual, enlarged, direct (Fig. 2.12)

Mirror formula

Let us find the connection between the optical characteristic and the distances that determine the position of the object and its image.

Let the object be a certain point A located on the optical axis. Using the laws of light reflection, we will construct an image of this point (Fig. 2.13).

Let us denote the distance from the object to the pole of the mirror (AO), and from the pole to the image (OA¢).

Consider the triangle APC, we find that

From triangle APA¢, we obtain that . Let us exclude the angle from these expressions, since it is the only one that does not rely on the OR.

, or

(2.3)

Angles b, q, g rest on OR. Let the beams under consideration be paraxial, then these angles are small and, therefore, their values ​​in radian measure are equal to the tangent of these angles:

; ; , where R=OC, is the radius of curvature of the mirror.

Let us substitute the resulting expressions into equation (2.3)

Since we previously found out that the focal length is related to the radius of curvature of the mirror, then

(2.4)

Expression (2.4) is called the mirror formula, which is used only with the sign rule:

Distances , , are considered positive if they are measured along the path of the ray, and negative otherwise.

Convex mirror.

Let's look at several examples of constructing images in convex mirrors.

2) The object is located at a distance equal to the radius of curvature. Imaginary image, reduced, direct (Fig. 2.15)

The focus of a convex mirror is imaginary. Convex mirror formula

.

The sign rule for d and f remains the same as for a concave mirror.

The linear magnification of an object is determined by the ratio of the height of the image to the height of the object itself

. (2.5)

Thus, regardless of the location of the object relative to the convex mirror, the image always turns out to be virtual, straight, reduced and located behind the mirror. While the images in a concave mirror are more varied, they depend on the location of the object relative to the mirror. Therefore, concave mirrors are used more often.

Having examined the principles of constructing images in various mirrors, we have come to understand the operation of such various instruments as astronomical telescopes and magnifying mirrors in cosmetic devices and medical practice, we are able to design some devices ourselves.

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 usually invisible in Everyday life, but creates 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 definitely 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 extending 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.

In school physics courses, any reflective surfaces are usually called mirrors. Considering two geometric shapes mirrors:

• flat
• spherical

- a reflective surface whose shape is a plane. The construction of an image in a flat mirror is based on , which, in the general case, can even be simplified (Fig. 1).

Rice. 1. Flat mirror

Let the source in our example be point A (point light source). Rays from the source spread in all directions. To find the position of the image, it is enough to analyze the path of any two rays and find the point of their intersection by construction. The first ray (1) will be launched at any angle to the mirror plane, and, according to , its further movement will be at the angle of reflection, equal to the angle falls. The second ray (2) can also be launched at any angle, but it is easier to draw it perpendicular to the surface, because in this case it will not experience refraction. The continuations of rays 1 and 2 converge at point B, in our case, this point is point A (imaginary) (Fig. 1.1).

However, the resulting triangles in Figure 1.1 are identical (at two angles and a common side), then the following can be taken as a rule for constructing an image in a plane mirror: when constructing an image in a flat mirror, it is enough to lower a perpendicular from source A onto the plane of the mirror, and then continue this perpendicular to the same length on the other side of the mirror(Fig. 1.2) .

Let's use this logic (Fig. 2).

Rice. 2. Examples of construction in a plane mirror

In the case of a non-point object, it is important to remember that the shape of the object in a plane mirror does not change. If we take into account that any object actually consists of points, then, in the general case, it is necessary to reflect each point. IN simplified version(for example, a segment or a simple figure), you can reflect the extreme points and then connect them with straight lines (Fig. 3). In this case, AB is an object, A’B’ is an image.

Rice. 3. Constructing an object in a plane mirror

We also introduced a new concept - point light source is a source whose size can be neglected in our problem.

- a reflective surface whose shape is part of a sphere. The logic of image search is the same - find two rays coming from the source, the intersection of which (or their continuations) will give the desired image. In fact, for a spherical body there are three fairly simple rays whose refraction can be easily predicted (Fig. 4). Let be a point light source.

Rice. 4. Spherical mirror

First, let's introduce the characteristic line and points of the spherical mirror. Point 4 is called optical center of a spherical mirror. This point is the geometric center of the system. Line 5 - main optical axis of a spherical mirror- a line passing through the optical center of a spherical mirror and perpendicular to the tangent to the mirror at this point. Dot F — spherical mirror focus, which has special properties (more on this later).

Then there are three ray paths that are simple enough to consider:

1. blue. A ray passing through the focus, reflected from the mirror, passes parallel to the main optical axis (focus property),
2. green. A ray incident on the main optical center of a spherical mirror is reflected at the same angle (),
3. red. A ray running parallel to the main optical axis, after refraction, passes through the focus (focus property).

We select any two rays and their intersection gives the image of our object ().

Focus- a conventional point on the main optical axis at which rays reflected from a spherical mirror and running parallel to the main optical axis converge.

For a spherical mirror focal length(distance from the optical center of the mirror to the focus) pure geometric concept, and this parameter can be found through the relation:

Conclusion: The most common ones are used for mirrors. For a flat mirror, there is a simplification for constructing images (Fig. 1.2). For spherical mirrors there are three beam paths, any two of which produce an image (Fig. 4).

Flat, spherical mirror updated: September 9, 2017 by: Ivan Ivanovich