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A man wears convex lens glasses of focal length 30cm in order to correct his eye ...

A man wears convex lens glasses of focal length 30cm in order to correct his eye defect. instead of the optimum 25cm, his least distance of distinct vision is
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  • A 14cm
  • B 28cm
  • C 75cm
  • D 150cm
Correct Answer: Option A
Explanation:
F = \(\frac{uv}{u - v}\)
F = +ve
v = -ve
30 = \(\frac {25 {\times} (-v)}{25 - (-v)}\)
v = \(\frac {25 {\times} (-v)}{25+v}\)
v = 14cm
(Note that either negative or positive values go to show the positioning and hence, they are not a strong necessity in your final answer.)

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