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A person is suffering from myopic defect. He is able to see clear objects placed at 15 cm. What type and of what focal length of lens he should use to see clearly the object placed 60 cm away

Physics-General

  1. Concave lens of 20 cm focal length    
  2. Concave lens of 12 cm focal length    
  3. Convex lens of 20 cm focal length    
  4. Convex lens of 12 cm focal length    

    Answer:The correct answer is: Concave lens of 20 cm focal lengthFor viewing far objects, concave lenses are used and for concave lens
    u = wants to see equals negative 60 c m; v = can seeequals negative 15 c m
    so from fraction numerator 1 over denominator f end fraction equals fraction numerator 1 over denominator v end fraction minus fraction numerator 1 over denominator u end fraction rightwards double arrow f equals negative 20 c m.

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