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 $ .



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