Light from a point source in air falls on spherical glass surface (n = 1.4 and radius of curvature 20 cm). The distance of light source from the glass surface is 150 cm. At what position is the image formed?

105 cm from glass surface in the direction of incident light

The correct answer is Option (2) → 105 cm from glass surface in the direction of incident light

Using lens maker formula for a spherical surface,

$\frac{μ_2}{v}-\frac{μ_1}{u}=\frac{μ_2-μ_1}{R}$

where,

$μ_1$ = Refractive index of Air = 1

$μ_2$ = Refractive index of glass = 1.4

$u$ = Object distance = -150 cm

$R$ = Radius of curvature = +20 cm

$⇒\frac{1.4}{v}-\frac{1}{-150}=\frac{1.4-1}{20}$

$⇒v=\frac{1.4}{0.01333}≃105cm$