$A$ lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the lens is

$A$ convex lens of focal length $f$ produces a real image whose size is $n$ times the size of an object. The distance of the object from the lens is

If the image formed by a thin convex lens of power $P$ has magnification $m$,then the image distance $v$ is:

$A$ thin double-concave lens is made of a very thin transparent material. It can be filled with air or two liquids $L_1$ and $L_2$ having refractive indices $n_1$ and $n_2$ respectively. The lens will converge a parallel beam of light if it is filled with ........

$A$ biconvex lens $(R_{1}=R_{2}=20 \ cm)$ has a focal length equal to the focal length of a concave mirror. The radius of curvature of the concave mirror is (Refractive Index of glass lens $= 1.5$) (in $cm$)

The refractive index of the material of a concave lens is $\mu$. It is immersed in a medium of refractive index $\mu_1$. $A$ parallel beam of light is incident on the lens. The path of the emergent rays when $\mu_1 > \mu$ is