Knowledge points and exercises of physical lens in the second year of junior high school

Lens: An optical element made of a transparent substance (usually glass) with at least one surface that is part of a spherical surface and acts as a refractive element of light.

Classification: 1. Convex lens: thin edges, ** thick.

2. Concave lens: thick edges, thin edges.

Main optical axis: A straight line through two spheres.

Optical center: There is a special point on the main optical axis, through which the direction of light propagation does not change. (The center of the lens can be thought of as the center of light).

Focus: The point at which the convex lens can make the rays parallel to the main axis converge on the main optical axis, which is called the focal point of the lens, which is represented by f.

Imaginary focus: The rays parallel to the main optical axis become divergent after passing through the concave lens, and the reverse extension line of the divergent rays intersects at one point on the main optical axis, which is not the convergence point of the actual rays, so it is called virtual focus.

Focal length: The distance from the focal point to the center of light is called the focal length, which is denoted by f.

Each lens has two focal points, focal lengths, and a center of light.

The role of the lens on light:

Convex lens: Acts as a converging light element.

Concave lens: Divergent to light.

Physical concepts are one of the bases for problem solving, and some of the conditions of many problems are implicit in related concepts, so we can dig out the hidden conditions from the analytical concepts and seek solutions to the problems.

The analysis of physical processes is an important part of problem solving, and through the analysis of physical processes, the intrinsic relationship and necessary conditions between physical quantities in the problem can be found.

Take good notes. Notes are not a record, but a simple and concise record of the key points and difficulties in the above-mentioned lectures, and write down the main points of the lecture and your own feelings or innovative opinions. so that it can be reviewed, digested.

Do a thorough review. In order to prevent the forgetting of the knowledge learned before, every once in a while, it is best not to exceed ten days, review all the knowledge learned before, which can be done by reading books, reading notes, doing questions, reflecting, etc.

1 Convex lens: thick in the middle and thin at the edges.

2 Concave lens: thin in the middle, thick at the edges.

3 Convex lenses have a converging effect on light, and concave lenses have a divergent effect on light.

4. Be able to find out the main optical axis, focal point, and focal length.

5 Object Distance (u) The distance from the object to the convex lens. Image distance (v) The distance from the image to the convex lens. Convex lens imaging rules:

Relationship between object distance and focal length Relationship between image distance and focal length Positive and inverted image Large and small images of the image of the virtual and real u>2f f2f inverted magnification of the real image u=2f not formed uf inverted and reduced real image. Slide projector: f < u < 2f into an inverted, magnified real image.

Magnifying glass: u f into an upright, magnified virtual image. Microscope:

Eyepiece: plays a magnifying role; Objective: f < u < 2f into an inverted, magnified real image Telescope:

Eyepiece: plays a magnifying role; Objective: U > 2F, into an inverted, magnified real image.

7 Know the causes of myopia and hyperopia. Correction: myopia is corrected with a convex lens (the convex lens is negative); Hyperopia is corrected with a concave lens (concave lens is positive).

8 Lens power: =1 f ( f focal length.

Mainly the imaging law of convex lens, such as cameras, projectors, magnifying glasses, myopia mirrors, telescopes, microscopes, telescopes, are all in the study of the convex lens imaging law after a grasp of the understanding, their common elements are convex lenses, the convex lens imaging law is good to understand, what are the imaging characteristics of different object distances, positive and negative will be good to solve the problem.

Hands-on experiments are the best way, and learning physics is inseparable from experiments.

The formula for object distance, image distance, and focal length is 1 u (object distance) + 1 v (image distance) = 1 f (focal length).

The easiest way is to do the experiment yourself according to the description of the topic and see the actual effect. It's very simple, and the impression will be very impressive.

Remember the saying: things near and far like get bigger. (The closer the candle is to the lens, the farther and bigger it must be to get a clear image.)

When u>2f, it becomes a real image of shrinkage and handstand.

When u=2f, it becomes an equal-large, inverted real image.

When U<2F, it becomes a large, inverted real image.