The image formed by a lens is due to which optical phenomenon?

The figure below shows a point source of light $S$,a convex lens $L$,and a plane mirror $M$. The three are placed such that rays of light from $S$ return to it after reflection from $M$. $(i)$ What is the distance $OS$ called? $(ii)$ To which point (left of $S$,on $S$,or right of $S$) will the rays return if $M$ is moved to the left and brought in contact with $L$?

The distance between the object kept at $2 \, m$ from a plane mirror and its image is $.....$ (in $, m$)

For what position of the object does a convex lens form an erect and virtual image?

Which of the following is the correct general form of Snell's law?

What does positive magnification mean?