Question

 A glass lens is immersed in water. How is the power of the lens affected

Answer 1

For a glass lens in air, n2=1.5, n1=1

For a glass lens in water: n1=1.33

so

let: (1/R₁)-(1/R₂)=X

1/f in water =(1.5/1.33  -1)X

            nearly =1/4 X

so the focal length of the lens becomes 4 times when immersed in water.

so power becomes 1/4 th