Задача id13120

An object is placed at a certain distance from a thin converging lens and its image is obtained on the screen. In this case, the linear increase turned out to be equal to V1. Then the object was brought closer to the lens at a distance L from its previous position. By moving the screen again, a clear image was obtained and the linear increase was measured. It turned out to be equal to V2. Determine the focal length of the lens.

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