1 formula method: optical bench is used to do the experiment of convex lens forming a real image, and the object distance u and image distance v are measured and recorded. According to the lens imaging formula, the lens focal length f is calculated, and the average value is taken after many measurements.

2 *** Yoke method: fix the position of light source and screen with optical bench, and measure the distance L between them. Put the convex lens with the focal length to be measured between them, and move the convex lens along the main axis, so that the image of the inverted light source appears twice on the screen.

Record the position of the lens when imaging twice, from which the moving distance d of the lens can be calculated, and the focal length f of the convex lens can be calculated according to the formula. This method is called * * * yoke method. This is one of the methods commonly used in laboratory to measure the focal length of convex lens.

3 parallel light focusing method: according to the characteristics of convex lens, parallel light (such as sunlight) is incident on the convex lens along the main axis direction, and a light screen parallel to the lens is placed on the other side. Adjust the position of the light screen to make the light spot on the light screen smallest and brightest. At this time, the distance between the lens and the screen is the focal length of the convex lens. This is a simple and convenient method for roughly measuring the focal length of convex lens.

4 far object imaging method: in the laboratory, far object imaging method can be used instead of parallel light focusing method to estimate the focal length of convex lens, which is similar to parallel light method; Adjust the position of the light screen, so that distant objects (such as objects in or out of the classroom window) can be imaged on the light screen, and the distance between the light screen and the lens is about the focal length of the lens.

Extended data

The imaging principle of convex lens is:

When an object is out of focus, it becomes an inverted real image on the other side of the convex lens. There are three kinds of real images: reduction, equal division and enlargement. The smaller the object distance, the larger the image distance and the larger the real image. The object is placed in focus and becomes an upright magnified virtual image on the same side of the convex lens. The greater the object distance, the greater the image distance and the greater the virtual image. It does not image when it is focused. When it is at twice the focal length, it will become a real image of an equal-length inverted head.

The convex lens can be used for magnifying glasses, glasses worn by presbyopia and hyperopia, cameras, film projectors, slide projectors, microscopes, telescopes, etc.

Baidu encyclopedia-convex lens