New Cartesian Sign Convention

 

 

New Cartesian Sign Convention :- To get the formula for reflection by spherical mirrors and refraction by spherical lenses, we have to follow a sign convention. We will use the Cartesian sign convention, according to which all distances are measured from the pole of the spherical mirror or the optical center of the lens.

According to the New Cartesian Sign Convention:-

1. All distances are measured from the pole of the spherical mirror.
2. The distances measured upwards (perpendicular to the principal axis) are taken as positive.
3. Distances measured downward (perpendicular to the principal axis) are taken as negative.
4. The distances measured in the direction of the incident rays are taken as positive &
5. The distances measured in the opposite direction of the incident rays are taken as negative.

Note: – The focal length and radius of curvature of a concave mirror are taken as negative, the focal length and radius of curvature of a convex mirror are taken as positive and the focal length and radius of curvature of a plane mirror is infinite.