LENS FORMULA AND MAGNIFICATION:
The relation between distance of object, distance of image and focal length for a lens is called lens formula.
Where, v is the distance of image, u is the distance of object, and f is the focal length of lens. Distance of object and image is measure from the optical centre of the lens. The sign for distance is given as per convention.
The lens formula is valid for all situations for spherical lens. By knowing any of the two the third can be calculated.
The ratio of height of image and that of object or ratio of distance of image and distance of object gives magnification. It is generally denoted by ‘m’.
m=`("Height of image h’")/("Height of object h")`
=`("Distance of image v")/("Distance of object u")`
The positive (+) sign of magnification shows that image is erect and virtual while a negative (-) sign of magnification shows that image is real and inverted.