When a plane wavefront is incident on a convex lens,the emerging wavefront becomes . . . . . . .

$A$ convex lens of refractive index $1.5$ has power $3D$. It is placed in a liquid of refractive index $2$. The new power of the lens is (in $D$)

$A$ double convex lens of glass of $\mu = 1.5$ has a radius of curvature of each of its surfaces equal to $0.2 \ m$. The power of the lens is:

The distance between an object and a divergent lens is $m$ times the focal length of the lens. The linear magnification produced by the lens is

$A$ 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 $\,cm$)

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: