Question

in lens formula and in mirror formula we take distance in which unit centimetres or metre.

Answer 1

we take in meters not in cm

Answer 2

It is a relationship between object distance, image distance and focal length of the lens. It is represented as: -
1/v-1/u=1/f

Image visualization:- As the object is brought closer to convex lens from infinity to focus, the image moves away from the convex lens from focus to infinity. The size of image is goes on increasing and the image is real and inverted.

Linear magnification (m): - The linear magnification is the ratio of height of the image to the height of the object. It is represented as: -
Linear magnification (m): - Height of image/Height of object
M=hi/ho=v/u

Interpret ion of m
If m is positive, image is virtual and erect.
If m is negative, image is real and inverted.
If |m|>1, hi>ho image is enlarged.
If |m|<1, hi<ho, image is diminished.

Distinction between a concave and convex Lens.
In convex lens image is appeared enlarged while in concave lens the image is appeared diminished.
Uses of lenses

In spectaclesIn optical instrument like camera, microscope, telescope etc.