Задача id10585

A diverging lens with a focal length of 10 cm is inserted into a hole in the screen, onto which a parallel beam of rays falls. A screen is located at a distance of 30 cm from the lens parallel to its plane. When replacing a diverging lens with a converging lens of the same diameter, the radius of the bright spot on the screen did not change. What is the focal length (in cm) of a converging lens?

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