Задача id13181

A point source of light, emitting uniformly in all directions, is located at a distance of 3 m from an ideal reflecting plane mirror. A screen is located at a distance of 1 m on the other side of the source. By what percentage will the illumination in the center of the screen change if a thin positive lens with an optical power of 1 diopter is placed at a distance of 1 m from the mirror?

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