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Students Questions, Students Analogies, and Instructor Thoughts

February 22, 2012

Questions from inquiry students after a day of exploring with lenses and a day of dissecting eyes:

How does the eye keep from the image from getting blurry when the pupil dilates really large?

If a lens makes images upside down, then it must make light rays cross, but where does that crossing happen?

What roles does lens play in the eye? Is it to magnify the image, to flip the image right-side up, or to focus the image?

Does a lens work more-or-less like a pinhole, or is it different?

What would happen if we put a lens in the box theater? Would it flip the image again?

Why does the eye need a lens when a hole all by itself is capable of making an image?

Is it the amount of curve in the lens or the thickness of the lens that determines its effect?

Is the lens in our eye more like the really curved lenses or the more flattened out lenses?

I can accept that a lens can focus the image behind a hole, but how can it make an image with no hole?

Does the lens making an image upside work the same way the curved mirror does?

What happens in the eye when things look blurry?

Some ideas about how the box is analogous to the eye:

The pin hole is the pupil–an opening the lets light inside

The cardboard is the sclera–the outside shell that keeps light out

The aluminum foil is the iris–it’s what we use to control the amount of light that gets in

The piece of paper is the retina–it is where the image lands

The air in the box is the vitreous humor–it is a transparent filling that light can go through

There is no optic nerve or brain with the box.

There is no lens with the box.

There is no cornea with the box.

My Thoughts

A big thing we are wrestling with is, “How do lenses work?” and “What’s the purpose of the lens in the eye”. I guess I see that there are two major inroads to lenses here:

My first thought focuses more on the idea that the lens make the image upside down, which to our class implies that light must be crossing somewhere. Our working theory right now is that inverted images are caused from rays crossing at a point. We have seen this to be the case with both pinholes and concave mirrors. To make progress in this direction, we’ll have to put some effort into shopping for ideas about what light could be doing when it enters the lens to provide for such a crossing point. With that, I imagine we could also try to pinpoint where that crossing might be happening, and explore what happens in regions in front of, at, and behind the crossing point.

The second route I see focuses more on how the lens seems to capable of unblurring a blurry image (at least with the right distances), which implies that the lens is somehow un-overlapping those overlapping landing areas. Our working theory is that blurry images are caused from rays of light (originating from different sources) overlap on a surface, due to large landing areas. With this approach, we’d have to shop for ideas about what light could be doing when it enters the lens to “unblur” the image on the screen. We could try to explore the conditions under which lenses will or won’t cause the “landing areas” to overlap.

What I like about these two approaches is that they build on theories we have already developed: “Inverted images are caused by crossing” and “Blurriness is caused by overlapping”… students are already thinking about these connections and asking these questions, so it seems authentic and productive to pursue these directions. I also hope that these two lines of inquiry would converge, I suppose I mean that in more ways that one.

I’m also struggling with how much guidance and structure to give students right now.

I’m also struggling with another brewing line of inquiry in class into how corrective lens work and what that has to do with needing corrective lens. Is this a separate line of inquiry or does it clearly support the others? Does this inquiry need to become after the two above have born fruit, or can all three co-occur? I really like how “real-life” and personal this line of inquiry is, and how students can experiment with their own glasses. Less need for special equipment. Do I need to sequence and order these inquiries, or can I let students go off along these lines more freely? Can I possibly support all these lines of inquiry, and pull of their integration when that time comes? Does that integration need to occur? If so, how much?

OK. Time for bed.

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