Which of the following statements is/are true about the principal axis of a spherical mirror? (i) It is normal to the mirror. (ii) Point of incidence always lies on the principal axis. (iii) Principal focus always lies on the principal axis.

Explanation

Let's examine each statement: (i) It is normal to the mirror. The principal axis is an imaginary line that passes through the center of curvature and the pole of the spherical mirror. This line can be considered normal to the mirror at the pole, as it is perpendicular to the tangent of the mirror at that point. So, this statement is true. (ii) Point of incidence always lies on the principal axis. The point of incidence can be anywhere on the mirror’s surface where a ray of light strikes, not specifically on the principal axis. So, this statement is false. (iii) Principal focus always lies on the principal axis. The principal focus of a spherical mirror is always located on the principal axis. This is true for both concave and convex mirrors, where the focus lies along this axis. Thus, this statement is true. Answer: Statements (i) and (iii) are true about the principal axis of a spherical mirror.