In the biprism interference experiment, the distance d between virtual light sources can be measured by lens secondary imaging method. How to prove d= radical sign d 1*d2 according to the law of convex lens imaging? Remember that the distance from light source to lens, lens to lens focus and lens focus are all m? f？ l？ , then m+f+l? Is a constant. According to similar triangles's two proportional formulas and Vieta's theorem, l 1*l2=f*f can be obtained. The ratio of focal length f to d/2 is constant, so we can calculate d*d=d 1*d2.

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.

The convex lens is refractive imaging, and the obtained image can be an inverted or reduced real image; Inverted, equal-sized real images; Inverted and enlarged real image; An upright magnified virtual image. Concentrate light. Concave lens is refractive imaging, which can only form an upright and reduced virtual image. The divergent effect of light.

Extended data:

When the object distance is equal to twice the focal length, the image distance is also twice the focal length, forming an inverted real image with equal size. At this time, the object distance is equal to the image distance, and the image is equal to the size of the object, and the object image is different.

In the experiment, it is necessary to adjust the heights of the convex lens and the light screen to keep their centers on the same horizontal line with the center of the candle flame, so as to ensure that the image of the candle flame can be formed in the center of the light screen.

During the experiment, keep the position of the convex lens unchanged, change the distance between the candle or light screen and the convex lens, and observe and record the experimental phenomena.

When the object distance is less than a focal length, an upright and enlarged virtual image is obtained; (When the object distance is equal to the focal length, no image will be formed at this time.) When the focal length is between one and two times, an inverted magnified real image will be obtained. Beyond the double focal length, the real image is reversed and reduced.

Baidu encyclopedia-convex lens imaging law