CH.9 Sign convention in mirrors.

The sign convention in mirrors is a set of rules used to assign positive and negative signs to distances measured in mirror problems (especially spherical mirrors) so that calculations become consistent. According to the New Cartesian Sign Convention: The pole (P) of the mirror is taken as the reference point. All distances are measured from the pole along the principal axis. Rules: Distances measured towards the incident light are taken as negative. Distances measured opposite to the incident light are taken as positive. Heights measured above the principal axis are positive. Heights measured below the principal axis are negative. In concave and convex mirrors: For a concave mirror, object is usually in front → object distance is negative. For a convex mirror, image is formed behind the mirror → image distance is positive. This sign convention is very important in using the mirror formula: 1f=1/v+1/u It helps in correctly predicting the position, nature, and size of images formed by mirrors.