9.2.3 Sign Convention for Reflection by Spherical Mirrors

. . Sign Convention for Reflection by Spherical Mirrors While dealing with the reflection of light by spherical mirrors, we shall follow a set of sign conventions called the New Cartesian Sign Convention . In this convention, the pole (P) of the mirror is taken as the origin (Fig.

. ). The principal axis of the mirror is taken as the x-axis (X’X) of the coordinate system. The conventions are as follows – (i) The object is always placed to the left of the mirror.

This implies that the light from the object falls on the mirror from the left-hand side. (ii) All distances parallel to the principal axis are measured from the pole of the mirror. (iii) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative. (iv) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.

(v) Distances measured perpendicular to and below the principal axis (along –y-axis) are taken as negative. The New Cartesian Sign Convention described above is illustrated in Fig. . for your reference.

These sign conventions are applied to obtain the mirror formula and solve related numerical problems.