Optics Question 685
Question: A plano-convex lens is made of refractive index of 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is
[Pb. PET 2000]
Options:
A) 400 cm
B) 200 cm
C) 100 cm
D) 50 cm
Show Answer
Answer:
Correct Answer: C
Solution:
$ \frac{1}{f}=(\mu -1)\ ( \frac{1}{R _{1}}-\frac{1}{R _{2}} ) $
$ \frac{1}{f}=(1.6-1)\ ( \frac{1}{60}-\frac{1}{\infty } ) $
$ =\frac{1}{100} $
$ \Rightarrow f=100cm $
