Derivation of lens formula or mirror equation; Sign Conventions. New Cartesian Sign Convention is used to avoid confusion in understanding the ray directions. Check out the Light Reflection and Refraction Class 10 Notes, Explanation, Light Reflection and Refraction Class 10 NCERT Solutions. Since, the centre of curvature and focus lie in front of the concave mirror, so signs of radius of curvature and focal length are taken as … For the measurement of all the distances, the optical center of the lens is considered. U= negative for both V= positive for real inverted and negative for virtual erect Refer to the diagram for clear visualization. This sign convention is known as New Cartesian Sign Convention. Sign is taken as – (negative) from pole of a spherical mirror towards object along the principal axis. In numericals, we need to calculate some things likeObject distanceImage distanceObject heightImage heightFocal lengthTo calculate them correctly, we need to find whether it is positive or negativeThe sign convention mentioned below helps us in itWe can see the sign convention in … Sign Convention for Spherical Mirror: Cartesian Sign Convention: In the case of spherical mirror all signs are taken from Pole of the spherical mirror, which is often called origin or origin point. The principal axis of the mirror is taken as the x-axis (X'X) of the coordinate system. Your No1 source for Latest Entrance Exams, Admission info ... Sign convention for convex and concave lens. We can see the sign convention in both Lens Some points to note Focal length of Convex Lens is positive Focal length of Concave Lens is negative Since object is always in front of the lens, object distance is always negative If a real image is formed, image is formed on right side, so image distance is positive In this convention, the pole (P) of the mirror is taken as the origin. Sign convention in the case of concave mirror: Since, object is always placed in front of the mirror hence the sign of object is taken as negative. Sign convention for reflection by spherical mirrors Reflection of light by spherical mirrors follow a set of sign conventions called the New Cartesian Sign Convention.