Wavelength and Frequency
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Properties related to periodic repetition of patterns:
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The amount of time, or distance needed before the system starts to repeat the pattern.
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The repetition may not be exact (see advanced topics).
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Amount of time is measured in seconds, minutes, microseconds or other amount of time. This repetition is called frequency.
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Amount of distance is length. Repetition in the space dimension is measured by wavelength.
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Water waves have repetitions at many different scales:
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Large ocean rollers can be miles long
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Breakers at the beach are several yards (meters) long or longer
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Ripples around a rock in a rough stream are inches or feet long
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Ripples around a rock in smooth water are less than an inch long
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Wavelength in the space dimension corresponds to frequency or period in the time dimension.
Frequency and wavelength are reciprocal measures:
mathematically, frequency = 1/wavelength
Long wavelengths correspond to low frequency
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High frequencies correspond to short wavelengths
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Sound waves can also be measured by distance (wavelength), but we primarily perceive (hear) these waves in terms of pitch or equivalently, tone or frequency.
A low pitched sound (bass guitar or drum, big dog barking) has a long wavelength in the spatial dimension.
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A high pitched sound (clinking a glass bottle, ringing a small bell, bird chirping) has a short wavelength
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The measure of frequency in time of a sound wave is called hertz, named after the German scientist Heinrich Hertz who studied sound waves in the 1800's.
Hertz is also the measure for frequency of radio waves, including microwaves which are used for cell phones and cooking. Radio wave frequencies are in millions of hertz (megahertz or Mhz). Microwaves are in billions of hertz (gigahertz or Ghz). Computer CPUs in the 21st century are also measured in terms of Mhz or Ghz.
Hertz is a common German name, and the Hertz car rental company was started by some one with the same name.
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The human ear can perceive sounds from about 20 cycles per second (hertz, or hz) to about 20,000 cycles per second. This corresponds to a wavelength in space from about 50 feet (15 meters, for 20 hz waves) to about 1/16 inch (1 millimeter, for 20,000 hz waves).
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