How to recite the law of convex lens imaging in junior middle school physics? (I didn't listen in class and didn't understand what it meant)

In optics, an image gathered by actual light, called a real image, can be accepted by the light curtain; On the contrary, it is called a virtual image, which can only be felt with the eyes. When talking about the difference between real images and virtual images, we often mention such a method of distinction: "The real images are all upside down, and the virtual images are all upright." The three virtual images formed by plane mirror, convex mirror and concave lens are all positive; The real image formed by concave mirror and convex lens, and the real image formed by pinhole imaging are all inverted without exception. Of course, concave lenses and convex lenses can also form real images, and the two real images they form are also inverted. So is the image of the human eye a real image or a virtual image? We know that the structure of the human eye is equivalent to a convex lens, so the image formed by external objects on the retina must be a real image. According to the above rule of thumb, the image of the object on the retina seems to be upside down. But anything we usually see is obviously upright. This problem, which conflicts with experience and law, actually involves the regulation of cerebral cortex and the influence of life experience.

When the distance between the object and the convex lens is greater than the focal length of the lens, the object becomes an inverted image. When an object approaches the lens from a distance, the image becomes larger and the distance from the image to the lens becomes larger. When the distance between the object and the lens is less than the focal length, the object becomes an enlarged image. This image is not the convergence point of the actual refracted light, but the intersection point of their opposite extension lines, which can not be received by the light screen and is a virtual image. The contrast of the virtual image formed by the flat mirror (which can't be received by the light screen, but can only be seen by the eyes). When the distance between the object and the lens is greater than 1 times the focal length, the object becomes an inverted image. This is like the convergence point of actual light, which can be accepted by the light curtain and is a real image. When the distance between the object and the lens is less than 1 focal length, the object becomes an upright virtual image. When the object is infinitely far away, the obtained image is infinitely close to 1 times the focal length, but it is always farther than 1 times the focal length.

Edit the difference between this paragraph and concave lens.

Different structures

The convex lens is composed of transparent mirror surfaces polished into spherical surfaces on both sides, and the edge of the convex lens is thin and the middle is thick. The concave len is composed of a transparent mirror body with concave spherical surface polished on both sides, and that edge of the concave lens is thick and the middle is thin. .

Have different effects on light.

Convex lenses mainly converge light, while concave lenses mainly diverge light.

Different imaging characteristics

The convex lens is refractive imaging, and the image can be upright or inverted; Virtual image and real image; Zoom in and out. Play the role of spotlight. Concave lens is refractive imaging, which can only be reduced to vertical virtual image. Play the role of astigmatism.

Lens and mirror

Lenses (including convex lenses) are instruments that transmit light and form images by folding the light. Light obeys the law of refraction. Mirror (including convex mirror) is an instrument that does not transmit light, but reflects back the image, and light obeys the law of reflection. The convex lens can be an inverted enlarged, equal-sized and reduced real image, or an upright enlarged virtual image. Parallel light can converge on the focal point, and the light emitted from the focal point can also be refracted into parallel light. Concave mirror can only become an upright and reduced virtual image, which is mainly used to broaden one's horizons.

Edit the details of this paragraph.

Object distance (u) and

Focal distance (f) Relationship between image distance (v) and focal distance (f)

Or object distance (u). Inversion of application features on the same side or different sides.

U & gt2f f<v & lt2f Inverted Camera Used to Restore Real Images?

U=2f v=2f, the demarcation point for measuring the focal length of the inverted real image.

F<u & lt2f v & gt2f Inverted Magnifying Real Image Projector

Slide projector?

U=f- (shooting similar parallel light from infinity) No imaging-the real and virtual demarcation point of focal length measurement of parallel light source.

U<f v>u vertical magnifying glass for virtual image on the same side. The virtual image is on the same side of the object, and the virtual image is behind the object.

(1) times the focal length, inverted to reduce the real image; The first focal length here refers to the distance from the point where the parallel light sources converge on the main optical axis through the lens to the optical center of the lens, and then the second focal length refers to the real image which is twice as far away. Double focal length to double focal length, inverted to enlarge the real image; There is no imaging at one focal length; Enlarge the virtual image of the vertical position within a focal length; The real image and the image are on different sides of the convex lens, and the virtual image is on the same side of the convex lens. (2) A focal length is divided into virtual focal length and real focal length, and the two focal lengths are different in size. The near-focus image of the object becomes larger and the far-focus image becomes smaller. The convex lens imaging law table shows the distance from the object to the center of the lens. The distance from the virtual image and the real image to the lens center applies the relationship between the object distance and the image distance. The 2f inversion of the real image reduces 2f >:v>；; F camera u>V u=2f Inverted image v=2f can be used to measure the focal length of convex lens U = V2F >；; U>f inverted magnified real image v & gt2f projector, slide projector, projector u < V u=f Non-imaging parallel light source: searchlight U.

Real image, a close-up image of an object is magnified by a focal point, and the two focal points are divided into large and small virtual images. The distant image of the object is magnified, the real image is reversed, and the distant image of the object is reduced. (4) As a virtual image, things and images are consistent from left to right and from top to bottom; As real images, things and images are left and right relative, and up and down relative. (5) Two demarcation points of convex lens imaging: 2f point is the demarcation point of real image enlargement and reduction; Point f is the dividing point between real image and virtual image.

Deductive method of editing this paragraph law

The imaging rule of convex lens is1/u+1/v =1/f (that is, the sum of the reciprocal of object distance and image distance is equal to the reciprocal of focal length. ) * * * There are two kinds of derivation methods. They are "geometric method" and "functional method"

Edit this geometric method

The title is shown in the right picture. It is proved by geometric method that1/u+1/v =1/f. The imaging law of convex lens is deduced by geometric method.

Solution ∵△ aboc ∽△ a 'b 'o ∴ ab: a 'b' = u: v ∵△ cof ∽△ a 'b 'f ∴ co: a 'b' = f: (v-f). Uvf) = VF/UVF ∴1/f-1/v =1/u, that is,1/u+1/v =1/f.

How to edit the function of this paragraph

The problem is as shown in the figure on the right. Prove1/u+1/v =1/f by the function method.

Solution 1 The picture on the right shows the schematic diagram of convex lens imaging. Where c is the length of the imaged object and d is the length of the image formed by the object. U is the object distance, v is the image distance, and f is the focal length. Step 2 (1) In order to solve this problem by the function method, the main optical axis of the convex lens is related (i.e. coincident) with the horizontal coordinate axis (X axis) of the plane rectangular coordinate system, the ideal refractive surface of the convex lens is related with the vertical coordinate axis (Y axis), and the optical center of the convex lens is related with the coordinate origin. Then: the coordinates of point A are (-u, c), point F is (f, 0), point A' is (v, -d), and point C is (0, c). (2) AA' and A'C extend in two directions into a straight line l 1, l2, which are regarded as two function images. As can be seen from the image, the straight line l 1 is a direct ratio function image, and the straight line l2 is a linear function image. (3) Let the analytical formula of the straight line l 1 be y=k 1x and the analytical formula of the straight line l2 be y = K2x+B, and substitute A (-u, c), A' (v, -d) and C (0) according to the meaning of the question. C) Substituting the corresponding analytical formula to obtain the equations: c =-u. K2 as the unknown solution, k 1=-(c/u)k2=-(c/f) ∴ The two resolution functions are: y =-(c/u) x y =-(c/f) x+.

Edit this routine memory

1 . u & gt； 2f, inverted reduced real image f < v & lt2f The abbreviation of the camera is: small outside and small inside (or the close-up image of the object is smaller) 2.u=2f. The inverted real image v=2f can be used to measure the focal length of the convex lens. Abbreviations are: paired inverted solid 3.2f & gtu> inverted magnified real image v & gt2f projector, slide projector, and projector. Abbreviations are: Chinese and foreign inverted images are stereoscopic (or the distant image of an object becomes larger). 4.u=f Non-imaging parallel light source: searchlight. Abbreviations are: no imaging at the point. 5.u.

Application of convex lens in editing this paragraph

The lens of a camera is equivalent to a convex lens, and the photographic negative is the image formed when taking pictures. Projectors, slide projectors, projectors, magnifying glasses, searchlights, cameras and video cameras all use convex lenses, which improve our lives and are used all the time. Hyperopia glasses are convex lenses and myopia glasses are concave lenses. In addition, the convex lens is also used for: 1, shooting, video recording 2, projection, slide show, film 3, special effect lighting (focusing into various colors) 4, magnifying virtual images of people, workpieces, maps, etc.

Examples of convex lens applications

1 grandma often does this when she reads the newspaper with a magnifying glass in order to see it more clearly. () A. The newspaper and magnifying glass don't move, and the eyes are farther away from the newspaper. B.the magnifying glass is farther away from the newspaper. C. the newspaper and magnifying glass are still, and the eyes are closer to the newspaper. D. The magnifying glass is closer to the newspaper. Analysis: The magnifying glass is a convex lens, which can be seen from the convex lens imaging experiment. It can also be concluded from the imaging principle that the light parallel to the principal axis is constant, but as the object moves away from the lens, the light passing through the optical center becomes more and more gentle, so the farther the intersection of the opposite extension lines of two rays is from the lens, the larger the image is. That is, when the focal length is less than 1 times, the closer the object is to the focal length, the larger the image is. So the answer is B. Example 2 Xiaoming is doing experiments with a magnifying glass with a relatively large diameter, stretching his arms to look at distant objects. He can see images of objects. The following statement is correct: () A. The light that enters his eyes must be from an image. Image must be a virtual image. C. The image must be inverted. D. The image must be magnified analysis: the magnifying glass is a convex lens, and he holds the convex lens in his hand. When he looks at distant objects with his arms outstretched, the object distance is much greater than twice the focal length, so the human eye is outside one arm, so the light entering the human eye must be refracted light that is converged and imaged and then separated. We see it as if it were emitted from an image. This image must be the true image of inverted restoration. So the answer is C. In option A, not all the light that enters the human eye comes from the image. Secondly, as an application example 3 of projector lens, movies are shown in rural areas. When testing the lens, I found that the image on the screen was a little small. How should I adjust the projector? () A. The projector is farther away from the screen and the film is farther away from the lens. B. The projector is farther away from the screen and the film is closer to the lens. C. The projector is closer to the screen and the film is closer to the lens. D. The projector is closer to the screen and the film is closer to the lens. Analysis: This is an application problem of convex lens. The focal length of the lens (convex lens) of a film projector is constant. According to the law of convex lens imaging, the closer the film is to the focus of the lens, the larger the image formed on the screen, and the farther the screen is from the lens. In convex lens imaging, the closer the object is to the focus, the bigger the image is and the farther it is from the convex lens (both real and virtual images have this law). On the contrary, the farther the object is from the convex lens, the smaller the real image is and the closer the image is to the focus. In concave lens imaging, the farther the object is from the concave lens, the smaller the image and the closer the image is to the virtual focus. As can be seen from the above analysis, the correct choice of this question is B. III. As an application example of camera lens 4. After filming graduation photo, a classmate wanted to take a single photo. Photographers should adopt the following methods: (a) make the camera close to classmates, and at the same time retract the lens and get close to the film; B) Make the lens close to the classmates, and at the same time, the lens extends forward away from the film; C) Keep the camera away from classmates, and at the same time retract the lens and approach the film; D) Keep the camera away from classmates, and at the same time, the lens extends forward and away from the film. Behind the lens is a black box, and the film is installed at the bottom of the black box, which is equivalent to a light screen; Take a single photo after the group photo, which seems a little bigger. When imaging, we should enlarge the image, narrow the object distance and increase the image distance, that is, lengthen the black box or extend the lens forward. As can be seen from the above analysis, the correct choice of this question is B. Example 5 When shooting objects at the bottom of the pool with a camera, if the camera position remains unchanged, compare the situation with and without water in the pool (assuming that the objects seen by human eyes are the same size in both cases), and then the water () A. The camera box is slightly shorter, and the image obtained will be slightly larger. B. The camera box is slightly shorter, and the image obtained will be slightly smaller. C. The camera box is slightly longer, and the image obtained. In order to get a clear image of the object on the film, the black box should be lengthened appropriately, and at the same time, the image on the film will be slightly larger than the original image. In this example, with and without water, the distance between the object at the bottom of the pool and the camera lens is different; Due to the refraction of light, when there is water in the pool, the object distance decreases. According to the imaging principle, the correct option is C. Example 6 When surveying and mapping maps, surveyors need to take pictures of the ground on the plane in the air, which is called aerial photography. If the focal length of the lens of the aerial camera is 50 mm, the distance from the negative to the lens is () A.10 mm B. It is slightly less than 50 mm. It is slightly greater than 50 mm. D. It is equal to 50 mm. Analysis: Aerial photography refers to taking pictures of the ground on the plane. Because the object is far away from the convex lens, it can be regarded as a result. The correct option of this question is C. Explain that there is no convex lens imaging law, and it is impossible to solve the problems related to the application of cameras, slide projectors and magnifying glasses. The best way to master these laws is to draw pictures. Therefore, after class, students should repeatedly draw images of objects in different positions on the convex lens. On this basis, they can master the tables listed in the analysis of knowledge points, and then they can do this kind of problems with ease. Law of concave lens imaging: only a reduced vertical virtual image can be produced. When a virtual image is formed, if it is enlarged, it must be produced by a convex lens, and if it is reduced, it must be produced by a concave lens. No matter what kind of lens, the generated virtual image must be positive and the generated real image must be negative. The imaging law formula of concave lens is1/u+1/v =1/f (u is the object distance, v is the distance, and f is the focal length, just like a convex lens). For a thin concave lens, when the object is real, it becomes an upright and reduced virtual image, just like the object in the lens. When the object is a virtual object and the distance from the concave lens to the virtual object is less than a focal length, it becomes an upright magnified real image, and the image and the object are on the same side of the lens; When the object is a virtual object, and the distance from the concave lens to the virtual object is twice the focal length, it is imaged at infinity; When the object is a virtual object and the distance from the concave lens to the virtual object is less than twice the focal length, it becomes an inverted magnified virtual image, and the image and the object are on different sides of the lens; When the object is a virtual object and the distance from the concave lens to the virtual object is twice the focal length, it becomes a virtual image with the same size as the object, and both the image and the object are opposite to the lens; When the object is a virtual object and the distance from the concave lens to the virtual object is more than twice the focal length, it becomes an inverted and reduced virtual image, and the image and the object are opposite to the lens. If it is a thick meniscus concave lens, the situation will be more complicated. When the thickness is large enough, it will be equivalent to a galileo telescope, and when the thickness is larger, it will be equivalent to a positive lens.

Memory formula

I found a small camera outside the Second Ring Road. Between the first and second sounds, I saw a huge projection. The first link is serious fraud. Note: ① Outside the second ring: beyond the double focal length ② Pick up: Pick up, real (real image). To, Inverted (Inverted) Application: Camera ③: Enlarge ④ False, Virtual (Virtual) ⑤ Meridian, Magnifier