A plano-convex lens made of refractive index 1.5 and having radius of curvature $\mathrm{R}=4 \mathrm{~cm}$ fits exactly into a planoconcave lens made of refractive index 1.3 and having the same radius of curvature $R=4 \mathrm{~cm}$ such that their plane surfaces are parallel to each other. The focal length of the combination is :

A beam of light parallel to the principal axis of a concave and convex lens, first passes through the concave lens of focal length 0.5 m and then through the convex lens of focal length 1.75 m . If the lenses are placed 1.25 apart, which of the given statement is true?

When a body of refractive index $\boldsymbol{\mu}=\mathbf{1 . 4}$ is put into a liquid, the body becomes invisible. What would be the refractive index of the medium?

A ray of light is travelling from glass of refractive index $\frac{3}{2}$ to water of refractive Index $\frac{4}{3}$. What is the minimum angle of incidence for which no light enters in to the water?