State and explain the New Cartesian Sign Convention for spherical lenses.
New Cartesian Sign Convention for spherical lenses:
New Cartesian Sign Convention is used for measuring various distances in the ray diagrams of lenses.
According to this convention:
1. Object is always placed on the left of the lens; i.e., light must fall on the lens from left to right.
2. All distances parallel to the principal axis are measured from the optical centre of the lens.
3. The distances along the direction of incident rays (along positive x-axis) are taken as positive, whereas the distances opposite to the direction of incident rays (along negative x-axis) are taken as negative.
4. Distances measured above the principal axis (along positive y-axis) are taken as positive.
5. Distances measured below the principal axis (along negative y-axis) are taken as negative.