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item   FREQUENCY-AND-WAVELENGTH
The concepts frequency and wavelength can best be explained with help of sound.
Sound is a vibration of air with which the vibration is a wave-shaped periodic change
in air pressure. The number of vibrations per second is called the frequency,
measured in Hertz (Hz). We are capable to notice air vibrations from roughly 20 Hz to
20 kHz (1 Kilohertz = 1000 Hz). A single wave has a maximum and a minimum value,
a peak and a valley. The maximum (or minimum) value is called the amplitude. The
greater the amplitude, the louder the sound. The wavelength of a vibration is the
distance that the wave has travelled after one complete
sequence, for instance the distance between two peaks.
This distance depends on the propagation speed of the
wave. The propagation speed of sound through air is about
330 meters per second. A vibration of one Hertz in air
consequently has a wavelength of 330 meters and a
vibration of 1000 Hz has a wavelength of 33 centimeters
(330 m/s : 1000 Hz). In water the propagation speed of
sound is about 1480 m/s. Through water sound propagates
faster than it does through air and the same soundwave,
with a frequency of 1000 Hz, in water therefore has a wavelength of 148 cm. The
frequency of light is in the order of 600.000 Gigahertz. The propagation speed of light
through vacuum is about 300.000 kilometers per second, giving it a wavelength in the
order of 500 nanometers. In older literature wavelength still is expressed in Ångström
(Å) where one Ångström equals one-tenth of a nanometer. 500 nm is therefore
equivalent to 5000 Å.   building
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