Questions

Remote objects are viewed through a converging lens with a focal length F=9 placed at a distance a=36 in front of the eye. Assume that the radius r of the pupil is approximately 1.5 mm. Choose the correct options.

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The minimum radius of the screen that should be placed behind the lens so that the entire field of view is covered is 0.5 mm.

The minimum radius of the screen that should be placed behind the lens so that the entire field of view is covered is 1.0 mm.

The screen must be placed in the plane S with its centre at point B.

The screen must be placed perpendicular to the plane S with its centre at point B.

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detailed solution

Correct option is A

Let us first neglect the size of pupil, assuming that it is point-like. Obviously, only those of the beams passing through the lens will get into the eye which have passed through point B before they fall on the lens (figure). This point is conjugate to the point at which the pupil is located.1F=1a+1b,b=aFa−F=12cmR=bar≃0.5mm, and the screen must be placed in the plane S with its centre at point B.

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