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?
Answer & explanation
Correct answer: option 2
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
$⇒\frac{1.4}{v}-\frac{1}{-150}=\frac{1.4-1}{20}$
$⇒v=\frac{1.4}{0.01333}≃105cm$