A convex lens of focal length 10 cm is used as a simple microscope. When the image of an object is obtained at infinity, the magnification is . The near point for normal vision is 25 cm.

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(2) 2.5. Given: f=10 cm, the final image at infinity, near point D=25 cm. Idea: with the image at infinity the object sits exactly at the focus and the eye is relaxed. The angular magnification of a simple microscope is then m=D/f — how much bigger the object looks through the lens than it does held at the near point. m=(25)/(10). So the magnification is 2.5. (Had the image been formed at the near point instead, the magnification would be 1+D/f=3.5 — slightly more, but the eye would have to strain.)

A convex lens of focal length 10 cm is used as a simple microscope. When the image of an object is obtained at infinity, the magnification is ______. The near point for normal vision is 25 cm.

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