Video Transcript
The following figure shows light
from a distant object being focused by an eye and light from a nearby object being
focused by the same eye. From which object is the light
focused correctly? (A) It is focused correctly from
the nearby object. (B) It is focused correctly from
the distant object. (C) There is no way to tell.
This question is asking us if light
from a nearby object or light from a distant object is being focused correctly. To figure this out, we need to
identify two things: which diagram represents the nearby object and which the
distant object and which diagram shows light that is focused correctly.
Let’s look at the two diagrams of
the same eye. In the first diagram, the eye
focuses the light rays next to the back of the eye, closer to the center. The second diagram shows the eye
focusing light rays on the back of the eye. When light is focused, it
converges, or meets, at a point. Light is focused correctly when
this point is on the retina. This is because the retina is the
part of the eye that is sensitive to light. If light is not focused on the
retina, we cannot clearly see.
If we recall that the retina is
located at the back of the eye, we can now say that light in the first diagram is
not focused correctly. This is because the point at which
the light rays meet is in front of the retina. Light in the second diagram is
focused correctly, as the point at which the light rays meet is on the retina.
We now need to identify if the
light entering the eye in the second diagram is from a nearby or distant object. If the object is faraway, then the
light from it is effectively parallel. This means that the light rays are
not moving further apart nor are they moving closer together. The light in this diagram is not
parallel; it is diverging. This means the light rays are
moving away from each other. Light from a nearby object
diverges.
The correct answer is therefore
option (A). It is focused correctly from the
nearby object.
