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

The diameter of the Sun is $1.4 \times 10^9 \, m$ and its distance from the Earth is $10^{11} \, m$. What is the diameter of the image (in $cm$) formed by a convex lens of focal length $2 \, m$?

$A$ lens having refractive index $1.6$ has a focal length of $12 \ cm$ when it is in air. Find the focal length of the lens when it is placed in water. (Take the refractive index of water as $1.28$) (in $mm$)

$A$ convex lens having refractive index $1.6$ has a focal length of $12 \text{ cm}$ when it is in air. The focal length of that lens when placed in water is (refractive index of water = $1.28$) (in $\text{ mm}$)

An unsymmetrical double convex thin lens forms the image of a point object on its axis. Will the position of the image change if the lens is reversed?

An object is placed at a distance of $f/2$ from a convex lens. The image will be