Question
(a) What is the focal length of a magnifying glass that gives an angular magnification of 8.0 when the image is at infinity?(b) How far must the object be from the lens?
Step 1
Step 1: The angular magnification (M) of a lens when the image is at infinity is given by the formula M = D/f, where D is the near point distance (usually taken as 25 cm for a normal eye) and f is the focal length of the lens. Show more…
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(a) What is the focal length of a magnifying glass that gives an angular magnification of 8.0 when the image is at infinity? (b) How far must the object be from the lens? Assume the lens is held close to the eye.
A magnifying glass is a single convex lens with a focal length of $f=+14.0 \mathrm{cm} .$ (a) What is the angular magnification when this lens forms a (virtual) image at - $\infty$ ? How far from the object should the lens be held? (b) What is the angular magnification when this lens forms a (virtual) image at the person's near point (assumed to be 25 $\mathrm{cm}$ )? How far from the object should the lens be held in this case?
A person with a near-point distance of $24.0 \mathrm{~cm}$ finds that a magnifying glass gives an angular magnification that is 1.25 times larger when the image of the magnifier is at the near point than when the image is at infinity. What is the focal length of the magnifying glass?
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