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The distance of distinct vision of a person is 50 cm. He wants to read a book placed at 25 cm. What should be the focal length of the spectacles?​
  • a)
    + 50 cm
  • b)
    + 25 cm
  • c)
    -25 cm
  • d)
    -50 cm
Correct answer is option 'A'. Can you explain this answer?
Verified Answer
The distance of distinct vision of a person is 50 cm. He wants to read...
'u' should be the least distance of distinct vision .

Hence a convex lens of focal length 50 cm should be used.
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Most Upvoted Answer
The distance of distinct vision of a person is 50 cm. He wants to read...
Given:
Distance of distinct vision (D) = 50 cm
Distance of the book from the person (u) = 25 cm

To find:
Focal length of the spectacles (f)

Formula:
Lens formula,
1/f = 1/v - 1/u
where,
v = distance of the image from the lens

Calculation:
Using the lens formula,
1/f = 1/v - 1/u
1/f = 1/50 - 1/25
1/f = (2 - 1)/50
1/f = 1/50

Therefore, the focal length of the spectacles (f) = 50 cm

Answer: Option A) 50 cm
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The distance of distinct vision of a person is 50 cm. He wants to read a book placed at 25 cm. What should be the focal length of the spectacles?​a)+ 50 cmb)+ 25 cmc)-25 cmd)-50 cmCorrect answer is option 'A'. Can you explain this answer?
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