Political Science 1020E Lecture Notes - Lecture 7: Sound Energy, Wavelength
2 Oct 2016
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Why does the sound seem softer when you are further away from speaker: 2 distinct reasons actually. Same amount of power over greater area: sound dissipates, ear only gets the intensity not all of the power. Intensity will be 1/4th if twice as far. Oversimplification, because speaker won"t be sending waves in perfect spheres: but it will still be proportional to 1/r2. Attenuation- energy gets lost in medium it"s traveling in. Some energy gets turned into ethermal of air molecules (random vibrations) Used to describe loudness of a sound. = 10log10(i/10-12 w/m2: i is intensity of sound. Threshold of human hearing: =decibels (db) Why log: turns enormous numbers to easier/smaller numbers o. Examples: yelling at a friend at i=10-5 w/m^2. A pipe where both ends are open: only particular wavelengths allowed. Have to have antinodes at both ends o. What if close one end: like soda bottle, one end open, one closed, what possible wavelengths could we set-up, open end.
