![]() ![]() And if you stood right in front of the doorway, you would be able to see light from inside the concert hall. But, if you moved away from the door and stood with your back to the building, you would see little light, whereas the sound would still be easily audible. The reason for the difference -that is, why sound diffraction is more pronounced than light diffraction -is that sound waves are much, much larger than light waves. ![]() Sound travels by longitudinal waves, or waves in which the movement of vibration is in the same direction as the wave itself. Longitudinal waves radiate outward in concentric circles, rather like the rings of a bull's-eye. The waves by which sound is transmitted are larger, or comparable in size to, the column or the door -which is an example of an aperture -and, hence, they pass easily through apertures and around obstacles. Wavelengths for visible light range from 400 (violet) to 700 nm (red): hence, it would be possible to fit about 5,000 of even the longest visible-light wavelengths on the head of a pin! Light waves, on the other hand, have a wavelength, typically measured in nanometers (nm), which are equal to one-millionth of a millimeter. Whereas differing wavelengths in light are manifested as differing colors, a change in sound wavelength indicates a change in pitch. The higher the pitch, the greater the frequency, and, hence, the shorter the wavelength. As with light waves -though, of course, to a much lesserĮxtent -short-wavelength sound waves are less capable of diffracting around large objects than are long-wave length sound waves.
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