Optics Question 447

Question: Consider an equiconvex lens of radius of curvature R and focal length $ f. $ If $ f>R $ , the refractive index $ \mu $ of the material of the lens

Options:

A) Is greater than zero but less than 1.5

B) Is greater than 1.5 but less than 2.0

C) Is greater than 1.0 but less than 1.5

D) None of these

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Answer:

Correct Answer: C

Solution:

[c] $ \frac{1}{f}=(\mu -1)( \frac{2}{R} ) $ Or $ f=\frac{R}{2(\mu -1)} $ Now, $ f>R $

$ \therefore \frac{R}{2(\mu -1)}>R $ Or $ \frac{1}{2(\mu -1)}>1 $ or $ 2(\mu -1)<1 $ Or $ \mu -1<\frac{1}{2} $ or $ \mu <( 1+\frac{1}{2} ) $ or $ \mu <1.5 $



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