$A$ plano-convex lens is made of a material with a refractive index of $1.6$. The radius of curvature of the curved surface is $60 \ cm$. The focal length of the lens is.....$cm$.

$A$ biconvex lens has a radius of curvature of magnitude $20\, cm$. Which one of the following options best describes the image formed of an object of height $2\, cm$ placed $30\, cm$ from the lens?

$A$ convex lens of focal length $f$ is placed somewhere in between an object and a screen. The distance between the object and the screen is $x$. If the numerical value of the magnification produced by the lens is $m$, then the focal length of the lens is

$A$ bi-convex lens made of glass (refractive index $1.5$) is put in a liquid of refractive index $1.7$. Its focal length will

$A$ convex lens of focal length $\frac{1}{3} \ m$ forms a real,inverted image twice the size of the object. The distance of the object from the lens is (in $m$)

The radii of curvature of the faces of a double convex lens are $10 \ cm$ and $15 \ cm$. Its focal length is $12 \ cm$. What is the refractive index of the material of the lens?