Define Magnification of a lens.

Explanation

The ratio of height of image` (h_(2))` to the height of the object` (h_(1))` is called Magnification (M).
`therefore "Magnification"=("Height of the image")/("Height of the oject")`
`therefore M=(h_2)/(h_1)`
Magnification can also be calculated by ratio of the image distance (v) to the object distance (u).
`therefore "Magnification"=("Image distance")/("object distance")`
`therefore M=v/u`
From (i) and (ii),
`therefore M=(h_2)/(h_1) =v/u`