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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 1000 feet. The students at one end had stop watches; the students at the other end had a loud noise maker; both groups had walkie-talkies. The noise maker was aimed at the group with the stop watches, and the sound was made while the transmit button of the walkie-talkie was pressed. At the other end, the noise was first heard through the walkie-talkie since radio waves travel at the speed of light. This was followed about one second later by the sound traveling directly through the air. The time elapsed between the two represents the time it took for the sound to travel that distance (since the radio wave arrives essentially instantaneously). 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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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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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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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, and imaginatively combined this with reflection and refraction, covered on day one of the program. |
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Spectral Analysis, or Unmixing Mixed-Up Colors... The human eye cannot distinguish colors when they are mixed. 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 used probes connected to computers to determine the relative amounts of red, green, and blue comprising the colors of ordinary objects. We then 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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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. Although we have endeavored to exclude photographs where permission has been denied, it is possible for errors to occur. 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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