Задача id13187

The image of the Sun is obtained on the screen using a thin positive lens. Determine the aperture of the lens if it is known that the illumination of the image of the Sun by rays passing through the lens is equal to the illumination of the screen by direct sunlight. The angular size of the Sun is a = 30 min. The aperture ratio of a lens is the ratio of the square of its diameter to the square of its focal length.

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