## What is Object Distance

Distance of Object from Optical Centre of the lens is called Object Distance

It is denoted by u

##

What is Image Distance

Distance of Image from Optical Centre of the lens is called Object Distance

It is denoted by v.

##

What is Focal length

We have already studied that

Distance of Principal Focus from the optical centre of the lens is Called Focal Length

It is denoted by f

## What is lens Formula

This formula denotes relationship between

- Object Distance (u)
- Image Distance (v)
- Focal length (f)

Note : -We follow the sign convention for lenses

In the image, the red text is negative, and blue text is positive

Thus,

- If Virtual image is formed,v is negative
- If Real Image is formed, v is positive
- Object Distance (u) is always negative as it is on left side of the lens
- Focal Length of Convex Lens is Positive
- Focal Length of Concave Lens is Negative

In addition to the mirror formula,

we have the magnification formula

## What is the magnification formula?

It is Ratio of Height of Image to the Height of Object

Hence it gives extent image is magnified compared to image of object

Suppose Height of object is h

Height of Image is h'

Magnification is m

So

Magnification = Height of Image/ Height of Object

m = h'/h

We also have another formula for magnification in lenses

Magnification = v/u

where

v is image distance

u is object distance

Note: - If magnification (m) is positive, It means image formed is

virtual and erect

If magnification (m) is negative, It means image formed isreal and inverted