CBSE Class 10 Science 2017 · Paper 531/1 · Question 23

(a) (i) Pole: the centre of the reflecting surface of a spherical mirror, a point on the mirror, written P. (ii) Centre of curvature: the reflecting surface is part of a sphere, and the centre of that sphere is the centre of curvature C; it lies in front of a concave mirror and behind a convex mirror. (iii) Principal axis: the straight line passing through the pole and the centre of curvature; it is normal to the mirror at its pole (see the diagrams). (b) (i) M is a concave mirror: the image Q is behind the mirror (virtual), erect and larger than the object, and only a concave mirror forms such an image. (ii) The object must lie between the pole and the principal focus, that is, at a distance of less than 15 cm from the mirror (0 to 15 cm). (iii) In the ray diagram a ray parallel to the axis is reflected through F and a ray along the line from C returns along itself; the reflected rays diverge, and their backward extensions meet behind the mirror to give a virtual, erect, enlarged image (for an object at 10 cm, the image is 30 cm behind the mirror and three times larger).