Why the Image seems to be behind the Mirror
If a candle is placed in front of a mirror, as in Figure 62, one of the rays of light which leaves the candle will fall upon the mirror as AB
and will be reflected as BC
(in such a way that the angle of reflection equals the angle of incidence). If an observer stands at C
, he will think that the point A
of the candle is somewhere along the line CB
extended. Such a supposition would be justified from Section 102. But the candle sends out light in all directions; one ray therefore will strike the mirror as AD
and will be reflected as DE
, and an observer at E
will think that the point A
of the candle is somewhere along the line ED
. In order that both observers may be correct, that is, in order that the light may seem to be in both these directions, the image of the point A
must seem to be at the intersection of the two lines. In a similar manner it can be shown that every point of the image of the candle seems to be behind the mirror.
It can be shown by experiment that the distance of the image behind the mirror is equal to the distance of the object in front of the mirror.
FIG. - A bouncing ball illustrates the law of reflection.
FIG. - The image is a duplicate of the object, but appears to be behind the mirror.