The following figure shows two
light rays from the same point that are both incident on different parts of a
concave mirror. When these light rays are
reflected, will the paths of the reflected light rays cross each other? (A) Yes, they will cross each
other. (B) No, they will not cross each
other. Or (C) there is no way to tell.
In this question, we’re shown two
light rays, A and B. These light rays are both incident
on a concave mirror. Let’s begin by labeling the optical
axis and the focal point of the mirror. With the optical axis labeled, we
notice immediately that incident ray A is parallel to the optical axis. This means that the reflected ray
of incident ray A will pass through the focal point of the mirror.
For incident ray B, this isn’t the
case. So, we will have to use the law of
reflection to determine where its reflected ray goes. The law of reflection tells us that
the angle of reflection of a ray of light is equal to its angle of incidence. And we should remember that these
angles are measured from the normal of the surface that the light ray is reflecting
off. Drawing the normal of the concave
mirror at the point that incident ray B reflects and its angle of incidence, we can
now draw the reflection of ray B.
Now that we’ve drawn both reflected
rays on the diagram, we can see that they cross at this point here. Therefore, answer option (A) is the
correct answer. When the two light rays are
reflected, yes, they will cross each other.