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A point object O is placed on the principal axis of a convex lens of focal length f = 20 cm at a distance of 40 cm to the left of it. The diameter of the lens is 10 cm . An eye is placed 60 cm to the right of the lens and a distance h below the principal axis. The maximum value of h to see the image is. (assume paraxial approximation to be valid here)

Options

  1. A0
  2. B2 . 5 cm
  3. C5 cm
  4. D10 cm

Correct answer

B. 2 . 5 cm

Step-by-step solution

1 v = 1 f ⁡ + 1 u = 1 2 0 - 1 4 0 = 1 4 0 v = 40 cm To locate field of view ray passing through upper end should be used. At location of eye, its height should not be below 20 tan θ from axis to see the image i.e., 2 0 5 4 0 = 2.5 cm

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