What do you understand by the term magnification? Write an expression for it for a lens, explaining the meaning of the symbols used.

The ratio of length of image I perpendicular to the principal axis, to the length of the object O, is called linear magnification.

The expression is:

$m = \dfrac{\text{length of image (I)}}{\text{length of object (O)}} = \dfrac{v}{u} \\[0.5em]$

where,

v = image distance

u = object distance.