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 $
