$A$ beam of light is incident through the holes on side $A$ and emerges out of the holes on the other face of the box as shown in the Figure. Which of the following could be inside the box?

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 $L$?

$A$ doctor has prescribed a corrective lens of power $+1.5\, D.$ Find the focal length of the lens. Is the prescribed lens diverging or converging?

How will you decide whether a given piece of glass is a convex lens,concave lens or a plane glass plate?

$A$ $10 \, cm$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $30 \, cm$. The distance of the object from the lens is $20 \, cm$. Find the $(i)$ position,$(ii)$ nature,and $(iii)$ size of the image formed.

For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram.