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frequency, amplitude and wavelength
The concepts frequency and amplitude 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 kilo
Hertz = 1000 Hz). A single wave has a minimum and a maximum value, a peak and a valley. The difference between them 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 speed with which the wave propagates itself through a medium. 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.
energy and intensity
In 1672 Isaac Newton revealed his hypothesis about the behaviour of light in which he stated that light consisted of small particles.
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
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This theory was contradictory to that of Christiaan Huygens who, in 1678, revealed his undulation theory in which he stated that the behaviour of light was comparable with that of a wave. In the end it turned out that both were partly right. In contrast with sound, that propagates as a pure wave, light behaves not only as a wave but also as radiation. The frequency of light is in the order of 600.000 Gigahertz. The propagation speed of light through vacuum is about
nanometer. 500 nm is therefore equivalent to 5000 Å. On the other hand light can be seen as a constant flow of small quantities of energy called photons. Photons possess a certain quantity of energy that is expressed in electron volts (eV) where one eV is the energy gained by an electron when it passes a potential of one Volt. The energy of radiation increases with its intensity,
which is proportional with the number of photons per second. This is why Y- and X-rays (see electromagnetic spectrum) are more harmful than for instance radio waves.