A short sighted person can see objects most distinctly at a distance of `16 cm`. If he wears spectacles at a distance of `1 cm` from the eye, what focal length should he have so as to enable him to see distinctly at a distance of `26 cm` ? ( c) The person above prefers to remove his spectacles while reading a book. Explain why ? (NCERT Solved Example)
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As the person wears spectacles at a distance of `1cm`. From the eyes. `:. u = - (26 - 1)cm = - 25 cm`, and `v = - (16 - 1)cm = - 15 cm , f = ?` As `(1)/(f) = (1)/(v) - (1)/(u)` `:. (1)/(f) = (-1)/(15) + (1)/(25) = (- 5 + 3)/(75) = - (2)/(75)` `f = - (75)/(2)cm = - 37.5 cm`. A concave lens of focal length `37.5 cm`. is to be used.
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