Video Transcript
The following figure shows two
light rays from the same point that are both incident on and reflected from
different parts of a concave mirror. What does point P, where the paths
of the reflected rays cross, represent? (A) The focal point of the
mirror. (B) The center of curvature of the
mirror. Or (C) the image of the point from
which the incident rays traveled.
This question is asking what point
P represents in terms of the reflected rays. To answer this question, we must
recall the definitions for focal point and center of curvature. And we must also recall the rules
for images produced by concave mirrors. Recall that the focal point of a
concave mirror is the point at which the reflected rays of parallel incident rays
all cross each other’s paths. Though it is true that both
reflected rays A and B cross at point P, incident rays A and B are not parallel. So, point P cannot be the focal
point.
The center of curvature of a mirror
is a point that is the same distance from the surface of the mirror in every
direction. Let us add some lines from point P
to random points on the surface of the mirror. We see that our lines, which are
yellow and purple, are not the same length. Therefore, point P cannot be the
center of curvature. This leaves us with point P being
the location of an image produced by incident rays A and B.
All light rays from the point of
origin that are reflected by the mirror will meet at point P. This means that at point P, an
image is formed of the part of the object that is at the point of origin. And therefore, the correct answer
is option (C). Point P, where the paths of the
reflected rays cross, represents the image of the point from which the incident rays
traveled.
