Optics Question 576

Question: The radius of curvature for a convex lens is 40 cm, for each surface. Its refractive index is 1.5. The focal length will be

[MP PMT 1989]

Options:

A) 40 cm

B) 20 cm

C) 80 cm

D) 30 cm

Show Answer

Answer:

Correct Answer: A

Solution:

By formula $ \frac{1}{f}=(\mu -1)( \frac{1}{R _{1}}-\frac{1}{R _{2}} ) $ = $ (1.5-1)( \frac{1}{40}+\frac{1}{40} )=0.5\times \frac{1}{20}=\frac{1}{40} $

$ \therefore $ $ f=40 $ $ cm $



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