(a) Refer to the diagram given below. A lens with two different refractive indices is shown. If the rays are coming from a distant object, then how many images will be seen?

(b) A glass lens always forms a virtual, erect and diminished image of an object kept in front of it. Identify the lens.

(a) Two images will be seen.
Reason — According to the lens maker formula :

$\dfrac{1}{\text{f}}$ = (μ - 1)($\dfrac{1}{\text{R}$1} - $\dfrac{1}{\text{R}2}$)

Focal length is a function of refractive index, hence for two different refractive indices there will be two different focal lengths.

Two different focal length implies two different images for same object. Hence 2 images will be formed.

(b) Concave lens