"Lens and its application" is a main content of the senior high school entrance examination. As a professional lens R&D and production company, we still have the following insights on the basic and in-depth knowledge of lenses. Regarding the summary of junior high school physical lens knowledge points, we have collected the following information for your reference, knowledge and skills in the chapter "Lens and its application":

1. Understand what is a convex lens, what is a concave lens, and understand the focal point and focal length of the lens.

2. Understand the effects of convex and concave lenses on light.

3. By observing the actual objects and board diagrams of the convex lens and the concave lens, two different structures of the two lenses can be obtained, and students will be able to grasp the essential characteristics of things through observation and be able to recognize the different characteristics of different things through observation.

4. Cultivate students' ability to research and explore new problems through experiments.

Knowledge points of the junior high school physics lens course:

一、The basic concepts and properties of lenses

二、Convex lens imaging law

三、Convex lens imaging dynamic analysis-the relationship between image distance and object distance

四、Lens optical drawing (special light)

五、Method of roughly measuring the focus of convex lens-sunlight focusing method

六、How to distinguish between convex lens and concave lens

七、Explore the imaging laws of convex lenses

八、Myopia, hyperopia and correction methods

九、Microscope and telescope

十、Concave lens imaging characteristics

Summary of the knowledge points of junior high school physics lens:

lens
1, convex lens:

(1) A lens with a thick middle and a thin edge is called a convex lens.

(2) Convex lens has a convergent effect on light.


2, concave lens:

(1) A lens with a thin middle and a thick edge is called a concave lens.

(2) The concave lens has a divergent effect on light.

3. The main optical axis and optical center of the lens:

As shown in the figure below: the straight line CC′ passing through the two sphere centers on the lens is called the main optical axis; there is a special point on the main optical axis, and the light passing through this point has the same propagation direction. This point is the optical center.

4. Focus and focal length of convex lens

(1) Focus: Convex lens can make light parallel to the main axis converge at a point on the main optical axis. This point is called the focal point of the lens and is represented by "F".


(2) The distance from the focal point to the optical center is called the focal length, which is represented by "f".

Interpretation of key points:

1. Any material with excellent light transmission properties can be ground into a lens, such as ice, crystal, diamond, polymer transparent resin, plexiglass, etc.

Lens is a model. Common objects such as near-sighted glasses, far-sighted glasses, magnifying glasses, and even a drop of water can be regarded as a lens.

2. Convex lens has a converging effect on light. It does not mean that the light must converge at a point or a convergent beam after passing through the convex lens.

Convergence is relative to the light when it is not refracted.

3. The concave lens has a divergent effect on the light. It does not mean that the light beam passing through the concave lens must be divergent or elongated and do not intersect. Divergence is relative to the light when it is not refracted.

Explore the law of convex lens imaging

Review of Senior High School Entrance Examination-Lens and Its Application Explore the law of convex lens imaging

1、Experimental purpose: Observe the conditions of the convex lens forming various images

2、Experimental equipment: convex lens, optical bench, candle, light screen, match

3、Experimental steps：

(1) For coaxial adjustment, place the candle, convex lens, and light screen on the optical bench in turn. Light the candle and adjust the center of the candle, convex lens, and light screen to approximately the same height.

(2 ) Place the candle farther away and move the light screen until a bright and clear candle flame appears on the light screen. Observe whether this is upside down or upright, enlarged or reduced. Measure image distance and object distance.

(3)  Move the candle to the convex lens so that the distance from the candle to the convex lens is equal, and move the light screen until a bright and clear candle flame image appears on the light screen. Observe the distance from the image to the convex lens, the inversion and size of the image. Measure image distance and object distance。

(4) Move the candle closer to the convex lens so that the distance between the candle and the convex lens is within the distance, and move the light screen until a bright and clear candle flame image appears on the light screen. Observe the distance from the image to the convex lens, the inversion and size of the image. Measure image distance and object distance.

(5) Keep the candle close to the convex lens, place the candle on the focus of the convex lens, move the light screen to see if the image can be imaged

(6) Move the candle to the focus of the convex lens, move the light screen, can I still see the candle flame image on the light screen?

Memory formula of convex lens imaging law:

"One focal point is divided into virtual and solid, and two focal length is divided into size; when it becomes a real image, the near image of the object becomes larger and the far image becomes larger; when it becomes a virtual image, the near image of the object becomes closer, but the image becomes smaller."

(1)"One focal length is divided into virtual and real": The object becomes a virtual image within one focal length, and a real image beyond one focal length.

(2)"Difocal size": The object distance is less than twice the focal length, and the image is enlarged (except for the focal point); the object distance is greater than the twice the focal length, and the image is reduced.

(3)"When it becomes a real image, the near object and the far image become larger": When it becomes a real image, the object gets closer to the lens, and the image moves away from the lens, and the image gradually becomes larger.

(4)"When it is a virtual image, the object is close to the image, and the image becomes smaller": When it is a virtual image, the object is close to the lens, the image is also close to the lens, and the image gradually becomes smaller.

Interpretation of key points:

When doing convex lens imaging experiments, in order to ensure that the imaging is in the center of the light screen. The center of the candle, convex lens, and light screen should be adjusted to be on the same straight line and at the same height.

Convex lens application

1、Camera: The lens is equivalent to a convex lens. The light from the object passes through the camera lens and then converges on the film to form an inverted, reduced real image.

2、Projector: The lens is equivalent to a convex lens. The light from the projection film passes through the convex lens to form an image, and then changes the direction of light propagation through a flat mirror, so that the screen becomes an inverted, enlarged real image.

3、Magnifying glass: an upright, enlarged virtual image.

4、Microscope: The focal length of the objective lens is short, and the object becomes an inverted, enlarged real image (like the lens of a projector) through it; the focal length of the eyepiece is longer, and the image formed by the objective lens passes through it into a magnified virtual image (like a magnifying glass).

5、Telescope: (Kepler telescope) The function of the objective lens is to make the distant object into a real image near the focal point, and the eyepiece is equivalent to a magnifying glass to enlarge the image.

Interpretation of key points

1、In order to make the image on the screen "upright" (face up), the slide should be inserted upside down.

2、The camera lens is equivalent to a convex lens, and the film in the dark box is equivalent to a light screen. We adjust the focus ring, not the focus, but the distance from the lens to the film. The farther the object is from the lens, the film should be closer to the lens.

Eyes and glasses

1、Myopia and hyperopia:

2、Degree of glasses:

(1) Power: The shorter the focal length of the lens, the greater the refractive power. The reciprocal of the focal length of the lens is called the lens power. Expressed by φ:

(2) When the focal length is in meters, the unit of power is diopter. The power of the glasses is the diopter multiplied by 100. For example, a convex lens with a focal length of 1/5m has a power of 5 diopters, and a hyperopic lens made of it is +500 degrees.

(3) Degree: The degree of the hyperopic lens is positive, and the degree of myopia is negative.

This is the summary of the knowledge points of physics lens in junior high school. Finally, I will teach you the simplest method to distinguish between convex lens and concave lens.

Convex lens and concave lens: a lens with a thick middle and a thin edge is called a convex lens, and a lens with a thin middle and a thick edge is called a concave lens.

Main axis: The straight line passing through the two spherical centers of the lens is called the main optical axis of the lens.

Optical center: The center point of a thin lens is called the optical center of the lens. The direction of light passing through the optical center remains unchanged.