Question Video: Identifying the Features of a Concave Mirror Science

Video Transcript

The following figure shows three parallel light rays incident on a concave mirror. Which of the following is the term for point P, which is shown by the black dot? (A) Center of curvature of the mirror or (B) focal point of the mirror.

To answer this question, let’s recall what the terms given in the answer choices mean, center of curvature and focal point. The center of curvature of a mirror is a point that is at the same distance from the surface of the mirror in any direction. To determine if point P is the center of curvature, we can draw new lines from P to different parts of the surface of the mirror and compare their lengths. It’s clear that these two lines have different lengths. Therefore, we can say that point P is not the center of curvature.

Meanwhile, the focal point of a curved mirror is a point at which the reflected rays of parallel incident rays all cross each other’s paths. We can see that all the incident rays are parallel. We also see that all the reflected rays’ paths cross at point P. Therefore, the answer is (B). Point P is the focal point of the mirror.