After a film, you walk out of a dark cinema hall into bright sunlight…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
After a film, you walk out of a dark cinema hall into bright sunlight. For a moment the light hurts and everything looks too bright. Explain with the iris and the pupil.
Need a reminder? The key ideaShow
The cornea and the eye lens form a real, inverted, small image on the retina, about behind the lens. The iris sets the size of the pupil. The ciliary muscles change the lens (accommodation). A normal eye sees clearly from its near point, about , to its far point at infinity.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. In the hall. In the dark, the iris had made the pupil large, to let in as much light as possible.
Step 2. Outside. In sunlight the wide pupil lets in far too much light, so everything glares.
Step 3. A moment later. The iris makes the pupil small, less light enters, and the eyes are comfortable again.
Answer: the pupil is still wide from the dark hall, and it takes a moment to shrink.
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