Demos - Demonstration ideas for teaching physics and physical science.

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Waves & Sound

32. Standing Waves

A DC motor is fitted with a small pulley attached to a swivel. The other end of the rope is attached to a stand with a swivel. As the speed of the motor is adjusted various numbers of nodes and loops can be created. A stroboscope can be used to "stop" themotion.
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33. Resonance
A tuning fork is held above a tube, the bottom of which is closed by the water in a 1 L graduated cylinder. The tuning fork and tube are raised and lowered together. The air column in the tube will resonate strongly at odd multiples of one fourthwavelengths of the fork.
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34. Freak Pipe
Frequency Pipe A long corregated plastic tube, open on both ends, is whirled around in a circle. The fundemental and several harmonics may be excited by whirling it at various speeds.
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35. Sympathetic Resonance***NEW!***
Two identical tuning forks are mounted on wooden resonance boxes. One of the tuning forks is excited and immediately dampened. The second tuning fork will resonate in sympathy with the first.
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36. Garden Trumpet***NEW!***
Trumpet Sound A 0.3 m section of discarded garden hose will produce a trumpet sound when blown as one blows a trumpet. Changing the length will change the pitch of the "trumpet".
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Light

37. Optical Transmitter

A tin can or paper tube is covered on one end by aluminum foil or mylar film. The aluminum foil should be stretched tight over the tube and held in place with a rubber band or tape. Sing and hold a note (the best you can) into the open end of the tube while reflecting the laser off of the center of the foil. Interesting lissajous figures will appear.
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38. Optical Voice Link

Credit for this technology goes to Alexander Graham Bell (who reportedly used the sun as the light source). A tin can or paper tube is covered on one end by aluminum foil or mylar film. The aluminum foil should be stretched tight over the tube and held in place with a rubber band or tape. Speak into the open end of the tube while reflecting the laser off of the center of the foil. The modulated signal is then picked up by a solar cell and amplified by a small audio amplifier.
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39. Periscope Reflection
A periscope is constructed from two plane mirrors set at 45 degree angles in a cardboard tube. The top of the periscope is constructed such that it can be rotated. When the top of the periscope is rotated 180 degrees the image produced is upside down. Properties of plane mirror reflection can be demonstrated.
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40. Refraction
$Refraction$ A polystyrene cup with a coin at the bottom is placed on a table. A student is asked to stand far enough away so that the coin is just out of view. As water is poured into the cup the coin comes into view.
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41. Concave Mirror
$Refraction$ A block of wax is mounted 50 cm away from a hotplate. Without the concave mirror behind it the wax will not melt.
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42. Reflection
Of the two concave mirrors the top one has a 4 cm hole so that light can escape. A coin is placed at the bottom of the bottom mirror. A surprisingly faithful three dimensional image is created in the opening.
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43. Total Internal Reflection
Internal_Reflection Punch a small hole near the bottom of a 1-L soft drink bottle. Fill the bottle with water. As the laser light exits the hole with the water, the water will appear red. Secretly depositing a drop of red food coloring in the pail can be humorous.
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44. Diffraction

$Diffraction$

A laser beam is directed onto a single slit cut into metal foil. Single slits of various widths may be shown to illustrate how the diffraction pattern width varies with the slit width.
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45. Polarization I
The polarization of laser light can be shown by rotating sheets of polarized film in the path of the laser beam.
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46. Polarization II
Polarization with flat panel The polarization of light from a flat panel display can be shown by rotating sheets of polarized film in the path of emitted light.
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Table of Contents

Waves & Sound

Light

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