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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 he can read the book when viewing through the magnifying glass ? |
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Answer» Solution :Here, f = 5 CM, U = ? For the closest distnace, `V=-25cm` As `(ul(1))/(upsilon)-(ul(-1))/(upsilon)=(-1)/(f)` `(1)/(u)=(1)/(v)-(1)/(f)=(1)/(-25)-(1)/(5)=(-1+5)/(25)` `u'=(25)/(-6)-4.2cm` This is the closest DISTANCE at which he can read the book. Forthe farthest distance, `v'=oo, u'=?` As `(1)/(f)=(1)/(v')-(1)/(u')` `(1)/(upsilon)=(1)/(v')-(1)/(f)=(1)/(oo)-(1)/(5)=(-1)/(5)` `u'=-5cm` This is the farhest distance at which he can real the book. |
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