A lens made up of different material forms two images of a point object ′O′ as shown in figure. Then
Let us assume that the refractive index of the upper part of the lens is μ1 and the lower part is made up of a material having a refractive index μ2. The more the refractive index more the light refracted, hence it can be observed that the light passing through μ1 is more refracted than the light passing through the refractive index μ2. Therefore it can be concluded that the refractive index of the upper part is more than the lower part of the lens. That means μ1>μ2 .