Optics Question 686
Question: The radius of the convex surface of plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is
[CPMT 2004]
Options:
A) 30 cm
B) 50 cm
C) 20 cm
D) 40 cm
Show Answer
Answer:
Correct Answer: D
Solution:
$ \frac{1}{F}=(1.5-1)\ ( \frac{1}{20}-\frac{1}{\infty } ) $
$ \Rightarrow F=40cm $ .
