Question

22. The focal length of a convex lens of glass (n = 1.50)
in air is 40 cm. Calculate the focal length of the lens
when it is immersed in a liquid of refractive index
(i) 1.30, (ii) 1.50, (iii) 1.70.​

Answer 1

Answer:(i) 130 cm, (ii) infinite (iii) -170 cm

Explanation:

Formula : Lens Maker formula

1/F = (n-1) [1/R1 - 1/R2]

Where

F= Focal length

n= refractive index

R= Radius of curvature

Formula : n=n1/n2

Refractive index of glass with respect to liquid =

refractive index of glass with respect to air/

(divided by)

refractive index of liquid with respect to air.