New Cartesian Sign Convention for the Object placed  in front of a spherical Lens (Concave or Convex) with the pole as an Origin and Principal Axis as an X-Axis are as follows:

  1. The object is always placed to the left of the lens. It means that the light from the object falls on the lens from the left-hand side.
  2. All the distances are measured from the pole of the spherical lens.
  3. All the distances measured parallel to the principal axis on the left (front) side (against the incident light) of the lens are taken with a negative (-ve) sign.
  4. All the distances measured parallel to the principal axis Right side (behind) of the lens ( ie. in the same direction of incident light) are taken with a Positive (+ve) sign.
  5. All the distances measured perpendicular and above to principal axis i.e. the erect image is taken as positive (+ve) and below (i.e. inverted image) is taken as negative (-ve).

Sign convention for Concave Lens (Diverging):

  1. Distance of object from the lens: As the Object is always placed in the left (front) of the Lens so, the object distance is taken always as negative (–ve).
  2. The radius of curvature (R) and focal length (f): As always virtual image is produced in the front (left) side of the Concave lens and thus the center of curvature and focus will be taken on the left (front) of the concave lens, Therefore radius of curvature (R) and focal length (f) of Concave lens are always taken as negative (-ve) 
  3. Distance of image from the lens: As always virtual image is produced in the front (left) side of the lens, so the image distance is taken as negative (–ve).
  4. Height of the image: The height of the image is taken as positive (+ ve) in the case of an erect image (above the principal axis) and taken as negative (- ve) in the case of an inverted image (below the principal axis).





Sign covention for Convex Lens (Converging):
  1. Distance of object from the lens: As the Object is always placed on the left side (front) of the lens so, the object distance is taken always as negative (–ve).
  2. The radius of curvature (R) and focal length (f): Both Real and virtual images can be formed on a Convex lens. But the radius of curvature (R) and focal length (f) of the Convex lens are always taken as Positive (+ ve) as per the new Cartesian convention. It does not depend on the type of image.
  1. Distance of image from the lens: When the image (i.e. virtual) is formed on the left side (front) of the convex lens, the image distance is taken as negative (–ve) and when the image (i.e. Real) is formed to the right side (behind) the convex lens, the distance of image is taken as positive (+ve).
  2. Height of the image: The height of the image is taken as positive (+ve) in the case of an erect image (above the principal axis) and taken as negative(-ve)  in the case of an inverted image (below the principal axis).






************************************

Shortcut Links For 


1. Website for School and College Level Physics   
2. Website for School and College Level Mathematics  
3. Website for Single National Curriculum Pakistan - All Subjects Notes 

© 2020-21 Academic Skills and Knowledge (ASK)     

Note:  Write to me in the comments box below for any query and also Share this information with your class-fellows and friends.