PART - 3 CH - 9 Light-Reflection and Eefraction — Science STD 10 — Question

Sign convention for spherical lenses:
In this case, optical centre O of the lens is taken as the origin and the principal axis of he ins is taken as the X-axis of the co-ordinate system. The Y-axis passes through O and lies in the plane of the figure.
(1) The object is always placed to the left of the lens as in case of a spherical mirror. This implies that light rays from the object fall on the lens from the left hand side.
(2) All distances parallel to the principal axis are measured from optical centre O of the lens.
(3) The distances measured in the direction of the incident ray are taken as positive while those measured in the direction opposite to the direction of the incident ray are taken as negative.
(4) The height measured above the principal axis of the lens and perpendicular to it. i.e.. in the upward direction is taken as positive, while that measured below the principal axis and perpendicular to it. i.e., in the downward direction, is taken as negative
Sign convention for a convex lens:

Object distance = - u
Object height =+h
Image distance =+ v for a real image
Image = - h' for a real image
Focal length = +f
Sign convention for a concave lens:


Object distance =-u
Image distance = - v
Focal length =-f
Object height = + h
Image height =+h'