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A man with normal near point (25 cm ) reads a book with small print using a magnifying glass : a thin convex lens of focal length 5 cm . a What is the closest and the farthest distance at which he should keep the lens from the page so that can read the book when viewing through the magnifying glass ? b. What is the maximum and the minimum angular magnification (magnifying power ) possible using the above simple microscope ? |
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Answer» SOLUTION :a. `(1)/(v) - (1)/(u) = (1)/(f), v = -25 cm, f = 5 cm` -`(1)/(25) - (1)/(u) = (1)/(5) , - (1)/(u) = (1)/(5) + (1)/(25) = (6)/(25) ` u = `(-25)/(6) cm = - 4.2 ` cm To see the object at the farthest POINT, its image must be FORMED at infinity. i.e., v = `- infty "" therefore - (1)/(u) = (1)/(5), u= -5 ` cm i.e., the object is placed at 5 cm from the magnifying GLASS b. maximum angular MAGNIFICATION = m = `(D)/(|u|) = (25)/(|(25)/(6)|) = 6 ` minimum magnification = `(D)/(|u|) = (25)/(|5|)= 5 ` |
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