Re: pinhole Image formation difficulties?

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Thu May 08 2003 - 14:19:14 PDT 

Message-Id: <l0311075dbae079a3ba08@[192.168.111.161]>
Date: Thu, 8 May 2003 14:19:14 -0700
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Image formation difficulties?

Many students have problems seeing the alignment of pins.

I use soda straws for these students.

Look through the straw at a point on the image.

I take a piece of corrugated cardboard about 9 Inches square
and hold straws to the cardboard by shoving pins through the straws.

If your students misbehave I have them wear eye protection so they don't
poke straws into other students eyes.

fast food Jack-in-the-box straws have large diameters and are easiest to use.

Paul D

>Hey Everyone!
>
>I use cardboard and two straight pins to make a "rifle sight" tool to help
>students see how mirrors form images. They line the sight up with the
>image in the mirror and use a ruler to draw rays to the mirror and back to
>the object, as well as extending the line behind the mirror. Repeating
>this from two or more sighting positions for each point on your object
>gives intersections that show where the virtual image would be. Using a
>simple assymetric shape, kids can see how mirror images get "flipped".
>This has worked well for me for a few years now.
>
>However, yesterday I ran into a problem I can't explain. I had one
>students who simply could not line up the sight. Even if someone else
>lined it up she would see multiple images. This persisted with one eye
>closed, then the other, then both open again. She was very disturbed that
>she had no success with the lab, and I can't figure out why she couldn't
>see the lined up pins. Any ideas or other hands-on image formation
>techniques would be appreciated.
>
>I think I may try a laser pointer to use as the ruler guide, but I'm not sure.
>
>Kevin Doyle
>
>
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