$A$ candle is placed at a distance of $10 \ cm$ from a plane mirror. At what distance from the mirror will the image of this candle be formed (in $cm$)?

An object is placed at a distance of $25 \, cm$ away from a converging mirror of focal length $20 \, cm$. Discuss the effect on the nature and position of the image if the position of the object changes from $25 \, cm$ to $15 \, cm$. Justify your answer without using the mirror formula.

How are power and focal length of a lens related? You are provided with two lenses of focal length $20\, cm$ and $40\, cm$ respectively. Which lens will you use to obtain more convergent light?

Where should an object be placed in front of a convex lens to obtain an image on the same side as the object?

$A$ concave mirror and a convex lens are held in water. What changes, if any, do you expect in their focal length?

$A$ convex lens of focal length $20 \, cm$ can produce a magnified virtual as well as real image. Is this a correct statement? If yes,where shall the object be placed in each case for obtaining these images?