Question

drive mirror formula and explain magnification

Answer 1

magnification is the ability of a lens or a mirror to diverge or converge light rays.

Answer 2

Whenever we observe an image of an object after refraction by a lens, there can be a change in the size of object i.e.
the image formed can have a larger size or smaller size than the actual size of the object.
This phenomenon of change in the image size is known as magnification.

Magnification is given by =

                                     Magnification = size of image / Size of object

i.e.

                                          m = -hi / h0

From figure = 

In similar ΔABO and ΔA′B′O

                               A′B / A′B′  =  B′O / OB

Putting values = 

                                -hi / h0 = +v / -u

                                 ∴ m = - vu

Where,

m = Magnification.

v = Image distance.

u = Object distance.

The negative sign indicates that the image is inverted.