Question

Light from a distant star is focused by the lens onto the retina (Intro 1 figure) . With a pupil diameter of 3.0 mm, the intensity of light falling on the retina is illustrated by the graph below (Intro 2 figure) . The spot illuminated on the retina is about 8 μm in diameter.

Light from a distant star is focused by the lens onto the retina (Intro 1 figure) . With a pupil diameter of 3.0 mm, the intensity of light falling on the retina is illustrated by the graph below (Intro 2 figure) . The spot illuminated on the retina is about 8 ?m in diameter.When star gazing on a very dark evening, the pupil diameter will expand to much larger than 3.0 mm . Part A With an expanded pupil diameter, what will happen to the the total amount of light energy reaching the retina? It will increase. decrease. stay the same. Part B With an expanded pupil diameter, what will happen to the spread of the image on the retina? It will increase. decrease. stay the same.

When star gazing on a very dark evening, the pupil diameter will expand to much larger than 3.0 .

Part A

With an expanded pupil diameter, what will happen to the the total amount of light energy reaching the retina?

It will

increase. decrease. stay the same.

Part B

With an expanded pupil diameter, what will happen to the spread of the image on the retina?

It will

increase. decrease. stay the same.

Answer 1

part A:

the total energy reaching the reina will increase with an expanded pupil diameter because the the incresed diameter of pupil eye will allow more light to fall on the retina

Part B:

from the diffraction condition it is clear that the pupil diameter is inversly preportional to the size of the image on the retina

so the spread of the image decrease with expanded pupil diameter