Optics Question 598
Question: A double convex lens of focal length 20 cm is made of glass of refractive index 3 / 2. When placed completely in water $ {( _{a}}{\mu _{w}}=4/3) $ , its focal length will be
[CBSE PMT 1990; MP PMT/PET 1998]
Options:
A) 80 cm
B) 15 cm
C) 17.7 cm
D) 22.5 cm
Show Answer
Answer:
Correct Answer: A
Solution:
$ f _{water}=4\times f _{air} $ , air lens is made up of glass.
