Ray Optics and Optical Instruments - Result Question 28
28. A double convex lens has focal length $25 cm$. The radius of curvature of one of the surfaces is double of the other. Find the radii if the refractive index of the material of the lens is 1.5.
[NEET Odisha 2019]
(a) $50 cm, 100 cm$
(b) $100 cm, 50 cm$
(c) $25 cm, 50 cm$
(d) $18.75 cm, 37.5 cm$
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Answer:
Correct Answer: 28. (d)
Solution:
(d) $\frac{1}{f}=(\mu-1)(\frac{1}{R_1}-\frac{1}{R_2})$
$\frac{1}{25}=(1.5-1)(\frac{1}{R}+\frac{1}{2 R}) \frac{1}{25}=0.5(\frac{3}{2 R})$
$2 R=37.5 cm \quad R=18.75 cm$
