A convex lens of glass `(mu_(g) = 1.45)` has a focal length f in air. The lens is immerseJ in a liquid Of refractive index (`mu_(I)`) 1.3. The ratio of the `F_(“liquid”)/F_(a)` is is

Options

A. 3.9
B. 0.23
C. 0.43
D. 0.39

Explanation

Focal length of lens when placed in air
`F_(air)=(mu_("lens")-1)((1)/(R_(1))-(1)/(R_(2)))`
Focal length of lens when placed in water `F_(air)=(mu_("lens")/(mu_(liq))-1)((1)/(R_(1))-(1)/(R_(2)))`
`(F_(liq))/(F_(air))=((1.45-1))/(((1.45)/(13)-1))=(0.45)/(0.15)xx13=3.9`