For optical radiation, the respective index of refraction is given in parenthesis Tab. 1: Velocities of sound and light in air and in water. The velocity of this propagation is generally abbreviated with the letter c (unit: meters per second, m / s) and depends on the medium and nature of the wave (see Tab. 1 below).
Yet, the result can still be described as a periodic change of a physical quantity (the strength of the electric and the magnetic field) propagating into space. In the case of an electromagnetic wave, the mechanism of propagation involves mutual generation of periodically varying electric and magnetic fields and is far more difficult to understand than sound. 2: Formation and propagation of a compression wave in air, a phenomenon colloquially called sound For example in the case of sound, the alternating rarefaction and compression of air molecules at a certain location results in periodic changes in the local pressure, which in turn causes the movement of adjacent air molecules towards or away from this location.įig. The propagation is caused by the fact that the vibration at a certain location influences the region next to this location. 1: Formation and propagation of a wave in a string Like all other waves (waves in a string, water waves, sound, earthquake waves …), light and electromagnetic radiation in general can be described as a vibration (more general: a periodical change of a certain physical quantity) that propagates into space.
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