Images and Shadows

Crossed Fingers-Students go outside (after the fog has cleared) and place their hands perpendicular to one another, making gaps between their fingers which are square in shape. The hands are then placed so that the sun's rays can shine through them. Observe the shape of the image that falls on the ground. This can also be accomplished using sunlight passing through the leaves of a tree, or you may choose to make a punchout hole-any shape other than round- in a piece of black construction paper.

What Shape is the Image?-In a darkened room, let light from a single bulb shine through a small hole onto a screen. The light should be placed at least one fourth of a meter from the screen. I have found that a flourescent tube, bent so that it mey be used in a normal lamp socket works well because of its irregular shape. Have the students rotate the bulb. See the Exploratorium booklet Bob Miller's Image Walk

Projected Image-Magic Wand, Snackbook

Animation Wheel-I was able to collect a set of these devices when MacDonald's gave them out in their Happy Meals.

Holes in the Box-In a large thin, black board drill a series of holes, ranging in size from one millimeter upwards. The holes should start small and widely dispersed on one side and graduate to larger and closer together on the other. I have attached my board to a support made of PVC pipe and drared the top with black fabric so that it is collapsible and light. Students look through the holes into the sunlight, using a screen of waxed paper or some other transluscent substance. They observe changeds in the size, focus and color of the image as the screen is moved varying distances from the holes. I have found the students get a better understanding of the orientation of the image if a partner goes out a nd walks back and forth in front of the board.

Inverse Square Law-Snackbook. See the decription of the LASE photodetector. The photodetector is mounted at the end of 2 meter sticks placed end to end. The detector is attached to a voltmeter. Students move a bulb away from the detector at 20 cm increments, record data, and graph results. I have students work in groups of three. One student graphs the data voltage vs. distance, the next voltage vs. 1/distance, and the third voltage vs. 1/distance ² .

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