Ray Optics And Optical Instruments Ques 68
68. 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
[2013]
(a) $2.5$ $ cm$
(b) $1.67 $ $cm$
(c) $1.5$ $ cm$
(d) $5$ $ cm$
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Answer:
Correct Answer: 68.(b)
Solution:
- (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 $ $m$
BETA
