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) There is no way to tell. (C) It is focused correctly from
the distant object.
This question is asking us if light
from a nearby object or light from a distant object is being focused correctly. To work this out, we need to
identify two things: which diagram represents the nearby object and which the
distant object and, secondly, which diagram shows light that is focused
correctly. The first diagram shows the eye
focusing light rays on the back of the eye. In the second diagram, the light
rays are focused to a point behind 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 see clearly.
If we recall that the retina is
located at the back of the eye, we can now say that light in the second diagram is
not focused correctly. This is because the light meets at
a point behind the retina. Light in the first diagram is
focused correctly, as the point the light meets is on the retina.
We now need to identify if the
light entering the eye in the first diagram is from a nearby or distant object. If the object is far away, then the
light from it is nearly parallel. This means that the light rays are
not moving further apart nor are they moving closer together. The light in the first diagram is
parallel; therefore, it is light from a distant object. The correct answer is then option
(C). It is focused correctly from the
distant object.
