An object is moving towards a converging lens on its axis. The image is also found to be moving towards the lens. Then,the object distance $u$ must satisfy:

Assertion : Position of image approaches focus of a lens,only when object approaches infinity.
Reason : Paraxial rays incident parallel to principal axis intersect at the focus after refraction from lens.

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

When a biconvex lens of glass having refractive index $1.47$ is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have a refractive index

Letters $A, B, C$ and $D$ are written on a cardboard as shown in the figure. The cardboard is kept at a suitable distance behind a transparent empty glass of cylindrical shape. If the glass is now filled with water,one sees an inverted image of the pattern on the cardboard when looking through the glass. Ignoring magnification effects,the image would appear as:

$A$ thin converging lens of focal length $f=25 \,cm$ forms the image of an object on a screen placed at a distance of $75 \,cm$ from the lens. The screen is moved closer to the lens by a distance of $25 \,cm$. The distance through which the object has to be shifted, so that its image on the screen is sharp again, is (in $\,cm$)