In the displacement method,the distance between the object and the screen is $70 \; cm$ and the focal length of the lens is $16 \; cm$. Find the separation between the magnified and diminished image positions of the lens. (in $; cm$)

When light rays from the sun fall on a convex lens along a direction parallel to its axis,which of the following statements is true?

$A$ substance is behaving as a convex lens in air and a concave lens in water. What is its refractive index?

$A$ biconvex lens has radii of curvature,$20 \ cm$ each. If the refractive index of the material of the lens is $1.5$,the power of the lens is .... $D$

For a concave lens of focal length $f$,the relation between object distance $u$ and image distance $v$ from its pole can best be represented by ($u = v$ is the reference line):

$A$ lens forms real and virtual images of an object when the object is at $u_1$ and $u_2$ distances respectively. If the size of the virtual image is double that of the real image,then the focal length of the lens is (Take the magnification of the real image as $m$)