bi-convex lens focal length 20 cm is made of glass of refractive index 1.5. When it is dipped in a liquid of refractive index 9/8 , it acts as a

Question

A thin bi-convex lens of focal length 20 cm is made of glass of refractive index 1.5. When it is dipped in a liquid of refractive index 9/8​, it acts as a:

Answer 1

The focal length of a lens is given by the formula, 

Since the focal length is coming out to be positive. It behaves like a convex lens of focal length 30 cm.