A mobile phone lying along the principal axis of a concave mirror . . .

Question : A mobile phone lying along the principal axis of a concave mirror, has its image formed as shown in the diagram below. Explain why the magnification is not uniform.

Doubt by Lakshita

Solution : 
The magnification produced by the concave mirror is given by 
m= h'/h = -v/u
where 

h' = height of the image
h = height of the object

v = image distance from the pole of the concave mirror

u = object distance from the pole of the mirror

From the formula, m=-v/u it is clear that object at different positions (u) will have different magnification. In the above figure, we can clearly see that different parts of the mobile phone are placed at different positions from the mirror, this is why the magnification of different part will be different and hence the image is distorted.