New Cartesian sign convention is used for measuring the various distances in the Ray diagram of spherical lenses ( Convex lenses and concave lenses ).
1. The object is always placed on the left side of the lens.
2. The distance measured in the same direction as that of incident light are taken as positive.
3. The distance measured against the direction of incident light are taken as negative.
4. The distance measured upward and perpendicular to the principal axis are taken as positive.
5. The distance measured downward and perpendicular to the principal axis are taken as negative.
6. The focal length of a convex lens is considered positive.
7. The focal length of a concave lens is considered negative.
Lens formula :
Lens equation or lens formula is an equation that relates the object distance u , image distance v and the focal length f of a lens.
1/f = 1/v - 1/u
Linear Magnification:
Linear Magnification (m) is defined as the ratio of the size of the image to the size of the object.
m = h2/h1 = v/u
If m is +ve then image is virtual and Eract.
If m is -ve then image is real and inverted.