Urgent, urgent. . All the knowledge about convex lens imaging should also have a title, and it is best to explain it clearly. If you are good, you will get extra points. . Urgently beg. .

A convex lens is a kind of lens with a thick central part. Convex lenses are divided into biconvex, plano-convex and concave-convex (or positive meniscus) and other forms. Thin convex lens is also called condenser because of its convergence, while thick convex lens has telescopic, divergent or convergent functions, which is related to the thickness of the lens. When parallel rays (such as sunlight) are parallel to the axis (the straight line connecting the spherical centers of the two convex lenses is called the main optical axis of the lens), the rays are refracted twice on both sides of the lens, and the point concentrated on the axis is called the focal point of the convex lens (denoted as F). A convex lens has a focal point on both sides of the mirror. If it is a thin lens, the distance between the two focal points and the center of the lens is approximately equal. The focal length of a convex lens refers to the distance from the focal point to the center of the lens, which is usually expressed by F. The smaller the spherical radius of the convex lens, the shorter the focal length. Convex lenses can be used for magnifying glasses, presbyopia and hyperopia glasses, microscopes and telescope lenses. The larger the focal length, the more convex the convex mirror surface, and the better the condensing function. A transparent body with two spherical surfaces or one spherical surface and the other flat surface and a thin middle part is called a concave lens. There are three kinds of lenses: biconcave lens, plano-concave lens and convex-concave lens. The line connecting the curvature centers on both sides is called the principal axis, and the point o in the center is called the optical center. The light passing through the optical center will not be refracted no matter where it comes from. The light beam parallel to the principal axis is refracted on the concave lens and then diverges in all directions, and the extension line opposite to its divergence direction will all be at point F on the same side as the light source, and its refracted light will just emanate from point F, which is called virtual focus. One on each side of the lens. Concave lens is also called divergent lens. The focal length of a concave lens refers to the distance from the focal point to the center of the lens. The larger the radius of curvature of a lens, the longer its focal length. If it is a thin lens, the focal lengths on both sides are equal. Focal length If you have seen "f =" in the English manual of the camera, then the number behind it is usually its focal length, that is, the focal length. For example, "f=8-24mm, 38- 1 15 mm (equivalent to 35mm)" means that the focal length of this camera is 8-24mm, and the oblique viewing angle is equivalent to 38- 1 15mm of the traditional 35mm camera. Generally speaking, the standard lens focal length of a 35mm camera is about 28-70mm, so if the focal length is higher than 70mm, it means that the telescopic effect is supported. If it is less than 28mm, it means that it has wide-angle shooting ability. "Focal range" is the extension of focal length, which is usually divided into general shooting distance and close-up distance. The general shooting distance of a camera is usually marked as "from a certain centimeter to infinity", and advanced products often provide close-up shooting function (macro) to make up for the problem of not focusing in general shooting mode. Some cameras emphasize the magical ability of supporting 1 cm close-up, which is suitable for shooting fine objects. The lens of a camera is a set of lenses. When the light parallel to the main optical axis passes through the lens, it will converge to a point, which is called the focus. The distance from the focal point to the center of the lens is called the focal length. A lens with a fixed focal length, that is, a fixed focus lens; The lens whose focal length can be adjusted and changed is a zoom lens. (When a beam of parallel light passes through the convex lens with its main axis, it will converge to a point on the other side of the convex lens, which is called the focal point, and the distance from the focal point to the optical center of the convex lens is called the focal length of the convex lens. There is a focal point on each side of the convex lens. ) optical center: the center of the convex lens can be approximately regarded as the optical center. The lens of the camera we use is equivalent to a convex lens, and the film (or the photosensitive device of a digital camera) is near the focal point of the convex lens, or the distance from the film to the optical center of the convex lens is about equal to the focal length of the convex lens. A convex lens with focal length can image. Generally, when a convex lens is used as the lens of a camera, the clearest image formed by it will not fall on the focus, or the distance from the clearest image to the optical center (image distance) is generally not equal to the focal length, but slightly larger than the focal length. The specific distance is related to the distance between the subject and the lens (object distance). The greater the object distance, the smaller the image distance (but always greater than the focal length). Because when we take pictures, the distance between the object and the camera (lens) is not always the same, such as taking pictures of people. Sometimes we have to shoot the whole body, we will be far away, and we will be very close when we take a bust. That is to say, the image distance is not always fixed, so if you want to get a clear image, you must change the distance from the film to the optical center of the lens with the different object distance. The process of this change is what we usually call "focus".

Lens and its application

I. Multiple choice questions (13×3 score =39 score)

1. Regarding the lens, the following statement is true ().

A. light will never pass through a concave lens. Light must converge to a point through a convex lens.

C. convex lens can only converge parallel light. A convex lens has two real focal points.

2. The following four optical devices imaging situation is correct ()

A. the camera becomes an upright and reduced real image. B. the projector becomes an upright and enlarged real image.

C. The magnifying glass becomes an upright and magnified virtual image D. The periscope becomes an upright and equal-sized real image.

3. Of the following statements about real image and virtual image, the correct one is ()

A. The real image is formed by the refraction of light, and the virtual image is formed by the reflection of light.

B. When seeing the real image, light enters the human eye, and when seeing the virtual image, no light enters the human eye.

C. the real image is reduced or enlarged, and the virtual image is enlarged.

D. the real image can be accepted by the light screen, but the virtual image cannot be accepted by the light screen.

4. Xiaoli wants to take a 2-inch registration photo after taking a 1 inch registration photo. What a photographer should do is ().

A. Close to Xiaoli, and the camera stretches forward. B. Get close to Xiaoli and retract the lens at the same time.

C stay away from Xiaoli, and at the same time, the lens extends forward. D. Stay away from Xiaoli, and at the same time, retract the lens.

5. When doing the convex lens imaging experiment, Xiao Yang observed an enlarged image on the screen 20 cm away from the convex lens. Then the focal length of this convex lens may be ()

A.5cm width10cm

C.15cm deep 25cm

6. In convex lens imaging, if the image you get is on the same side of the mirror as the object, then this image must be ().

A. Reduced and upright virtual image B. Enlarged and upright virtual image

C. Reduced and inverted real images D. Enlarged and inverted real images

7. As shown in the picture, Xiao Gang is holding a magnifying glass, looking at the object through the magnifying glass, and then seeing ().

A. it can only be an upright enlarged image.

B. you can only reverse the restore.

C. it can only be inverted.

D. all three images can be seen.

8. As shown in the figure, in the experiment of studying the imaging characteristics of convex lens, a clear candle flame image appeared on the right light screen.

Given that the focal length of the convex lens is f, it can be judged that the range of the distance u from the left candle to the convex lens is ().

A.u