OPTICS–PATHWAYS OF LIGHT - Trash for Teaching

TEACHER RESOURCES

OPTICS–PATHWAYS OF LIGHT

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Kit Activities:

Project H: Modify the pinhole camera
1. Make the hole a little smaller by covering part of it with your finger.
What do you notice? (Answer: The image gets fainter but sharper.)
2. Move your fingers out of the way so that both holes are completely
uncovered. What happens? (Answer: You see two images.)

Figure 3 Figure 4 Figure 5
3. Take the piece of the flap you cut off earlier. Cut it into three small
squares, each about half an inch on a side. Tape one of the squares to
the box so that it covers half of one of the holes; this turns the hole into
a smaller hole. Place a second square so that it completely covers that
hole. Tape it on one side only, to make a hinged flap that you can open
and close. Finally, place the third square so that it completely covers the
other hole, and tape it on one side only to make a hinge. (Figure 6)

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4. Use the hinged flaps to experiment with the holes. Cover the smaller
hole and uncover the larger one. Cover the larger hole and uncover the
smaller one. Uncover both holes. One of the holes produces a fainter but
sharper image. The other produces a brighter but fuzzier image. Which
is which, and why? (Answer: The smaller hole produces a fainter but
sharper image. As with the ants, when the hole is smaller, each place on
the wall of the box “sees” a smaller part of the light source.)
5. Use a pencil or similar object to poke a medium-sized hole through
the center of the closed end of the box. Halfway down the box, cut a slit
through any two adjacent sides (the easiest way to do this is to flatten
the box again and use scissors to cut 2 sides half way through to the
middle of the box.) (Figure 7) Set the box back up and slip a piece of
paper into the slit. (Figure 8)

Figure 6 Figure 7 Figure 8

6. Point the end of the box at your light source and look into the box.
Can you see an image on the piece of paper? What do you notice about
the image? (Figure 9) (Answer: It is now reversed; this is because you
are viewing it from the other side.) Move closer to your light source.
What happens to the image? (Figure 10) (Answer: It becomes larger.)
Explain this in terms of our thought experiment with a table full of ants.

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Figure 9 Figure 10

7. Take the box away from your face, remove the piece of paper from the
slot, hold it across the open end of the box, and without putting the box
to your face, point the closed end of the box at the light source again.
What happens to the image? (Answer: It is larger, fainter, and sharper.)
Explain it in terms of the thought experiment.

12815 S. Western Ave. Gardena, CA | trashforteaching.org | 310.527.7080 | [email protected]