BPSC 71st Prelims Exam Held on 13 Sep 2025

Concept:Focal distance is the distance from the mirror's pole to its focus, where parallel rays either meet or appear to meet. A plane mirror has no curvature, so it cannot focus light.Explanation:A plane mirror is flat with zero curvature. It neither converges nor diverges parallel rays; they reflect in parallel. Therefore, it has no real or virtual focus. The focal length of a spherical mirror is half its radius of curvature: $f = \frac{R}{2}$. For a plane mirror, the radius of curvature $R$ is infinite. So, $f = \frac{\infty}{2} = \infty$. Thus, the focal distance is considered infinite.Answer:Option D: Infinity