Question

At what distance from a converging lens of focal length 12 cm must an object be placed in order that an image of magnification 1 will be produced? 

Answer 1

Magnification 1 means that the image distance is the same as the object distance and the size of image is the same as the object.
This happens only if the position of the object is at 2f, i.e,`2xx` focal length.
Thus, the object must be placed at a distance of 24 cm`(2xx12)` from the converging lens.