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Measuring the Speed of Sound... On Tuesday morning, we all went outside to measure the speed of sound. We divided into two groups and separated by almost 1000 feet. The students at one end had stop watches; the students at the other end had a loud noise maker and an electronic flash; both groups had walkie-talkies. The noise maker and electronic flash were aimed at the group with the stop watches, and the sound and flash were made at the same time. At the other end, the flash was seen first since light travels so fast that it gets there almost instantly. This was followed about one second later by the sound traveling through the air. The time elapsed between the two represents the time it took for the sound to travel that distance. By dividing the distance by the elapsed time, they determined the speed of sound. It is about 330 meters per second, or about 740 miles per hour near the surface of the Earth. |
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It was a long walk back to the building. Check out the video on the left. Click the play button on the photo. |
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Learning about Sound Waves and Measuring the Frequency and Wavelength of Sound... After learning about waves and the particular nature of sound waves, students proceeded to measure the frequencies and wavelengths of sound waves, made at various pitches using special sound generators. They used oscilloscopes to measure the time that elapsed between the passage of one wave peak and the next. This is the number of seconds per wave. By turning this upside down (dividing it into one), they arrived at the number of waves per second. This is called the "frequency." They then determined the wavelength, that is, the distance between one wave peak and the next. Your voice can produce a wide range of frequencies, but a typical one at 500 cycles per second (Hertz) corresponds to a wavelength of about 0.66 meters. The A above middle C has a frequency of 440 Hertz, corresponding to a wavelength of about 0.75 meters. We even shattered a wine glass with sound waves!
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In order to show us a scream on the oscilloscope, Dr. DeLeo staged a make-believe horror movie called "Beauty and the Beast" (he was the beast). Click the play button on the photo on the left to see the video. |
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Check out the video to see sound waves squeezing and stretching the wine glass before it shatters. Click the play button on the photo on the right to see the video.
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Learning about Light Waves and Measuring the Frequency and Wavelength of Light... Using our treatment of sound as a basis, we proceeded to understand light in the context of waves. We discovered that brightness is analogous to loudness and color is analogous to pitch, although the ear and the eye behave quite differently. We measured the wavelength of light by making use of the fact that a bright spot appears when the peaks of light waves all line up. The wavelengths and frequencies of the lights from red and green laser pointers were measured very accurately. The wavelength of the light from a red laser pointer is about 650 nanometers (.00000065 meters) and the frequency is about 500,000,000,000,000 Hertz (cycles per second)!
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  Although our ears can distinguish a mixture of different pitches, our eyes cannot distinguish a mixture of colors (we simply perceive another color!). Light that looks white to our eyes is actually a mixture of all colors. These colors can be separated by using a prism or a diffraction grating to create a spectrum. A rainbow is an example of a spectrum. Students saw how red and green lights mixed to produce yellow. White light is actually a mixture of all the colors in the rainbow. Ultraviolet and infrared light are parts of the spectrum that human eye can’t see, like sound pitches that are too high or too low for the human ear to perceive. |
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Dr. DeLeo had an infrared thermometer, which he bought at Radio Shack. If you aim it at something, it tells you its temperature by measuring the infrared energy it gives off. The temperature of part of the slide projector that was just turned on was over 100 degrees. |
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Measured from the mouth, the student body temperatures were about 95 degrees.
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There is a relationship between our blue sky and red sunsets. As sunlight - a mixture of visible colors - passes through our atmosphere, small particles scatter blue light more effectively than the red end of the spectrum. Hence, the sky appears blue. Near sunset, when the sunlight is passing through a lot of atmosphere, so much of the blue end of the spectrum is scattered out that the remaining rays from the sun appear to be reddish. This was demonstrated by placing a small amount of dry milk (less than a teaspoon) in water, and shinning a flashlight through the water. The dry milk particles simulate the particles in our air, and the flashlight simulates the sun. Notice how the beam goes from bluish-white to reddish as it passes through the water.
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The Nature of Color, and Other Wave Properties of Light... On Wednesday morning, after discussing how I created a 3d photo of the class (shown at the end), we proceeded to examine a property of light called polarization (not represented by photographs below). This was followed by an examination of the human eye and how it detects color. Students experimented with mixing up to three colors. |
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In the video on the right, a student shows us how colors can be mixed. She first uses red and green filters to produce red and green beams of light. As these are brought together, they produce yellow (she points to the yellow). Then, she adds a blue beam of light and points to the resulting white produced by an additive mixture of red, green, and blue. Click the play button on the photo to view the video.
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Spectral Analysis, or Unmixing Mixed-Up Colors... The human eye cannot distinguish colors when they are mixed. As we saw, the right combination of red and green (when mixed additively, like when projected) will appear indistinguishable from yellow. Prisms and diffraction gratings bend rays of light by different amounts depending on the color, hence separating the colors. Students examined electrically excited gases and discovered that every type of atom emits its own characteristic set of colors ("spectral lines"). These colored lines are like fingerprints of the elements. |
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The student appearing in the video on the left explains it even better than I did! Click on the play button to see the video. |
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Here is a photograph of us in 3d. Use red-cyan glasses to view it.... |
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I hope you have enjoyed this web presentation as much as we enjoyed sharing the actual learning experience with your son or daughter. If you would like us to remove a photograph of your son or daughter for any reason, please send me an e-mail message at lgd0@lehigh.edu or call me at 610-758-3413, and we will remove it promptly. Please note that we will never associate a child's full or last name with a photograph except in circumstances where special permission was explicitly provided. Thank you. Gary DeLeo. |
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