A convex lens of focal length 12.5 cm is used as a simple microscope. When the image is formed at infinity, the magnification is . (Near point for normal vision is 25 cm.)

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Accepted Answer

(3) 2.0. Given: f = 12.5 cm, near point D = 25 cm, final image at infinity. Idea: with the image at infinity the object sits at the focus and the eye is fully relaxed; the angular magnification is then m = D/f. m = (25)/(12.5) = 2.0. Bringing the image to the near point instead would give m = 1+D/f = 3.0 -- slightly larger, but the eye has to strain for it. So the magnification is 2.0.

A convex lens of focal length 12.5 cm is used as a simple microscope. When the image is formed at infinity, the magnification is ______. (Near point for normal vision is 25 cm.)

Step-by-step solution

Why the other options are wrong