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.



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