Ray Optics and Optical Instruments - Result Question 67

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71. For a normal eye, the cornea of eye provides a converging power of $40 D$ and the least converging power of the eye lens behind the cornea is $20 D$. Using this information, the distance between the retina and the eye lens of the eye can be estimated to be

======= ####71. For a normal eye, the cornea of eye provides a converging power of $40 D$ and the least converging power of the eye lens behind the cornea is $20 D$. Using this information, the distance between the retina and the eye lens of the eye can be estimated to be

3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed:content/english/neet-pyq-chapterwise/physics/ray-optics-and-optical-instruments/ray-optics-and-optical-instruments—result-question-67.md (a) $2.5 cm$

(b) $1.67 cm$

(c) $1.5 cm$

(d) $5 cm$

[2013]

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Answer:

Correct Answer: 71. (b)

Solution:

  1. (b) $P _{\text{cornea }}=+40 D$

$P_e=+20 D$

Total power of combination $=40+20=60 D$

Focal length of combination $=\frac{1}{60} \times 100 cm$

$=\frac{5}{3} cm$

For minimum converging state of eye lens,

$u=-\infty \quad v=? \quad f=\frac{5}{3}$

From lens formula,

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u} \Rightarrow v=\frac{5}{3} cm$

Distance between retina and cornea-eye lens

$=\frac{5}{3}=1.67 m$