The standing wave is the phenomenon of an interference as a result of imposing of two passers in parallel going at each other signals. It arises at reflection of a signal from a barrier. Fluctuations of strings or air in musical instruments can be examples of standing waves.
Introduction
Standing waves can be formed under various conditions. The easiest to show this phenomenon in the conditions of limited space. Such effect can achieve by means of combination of two fluctuations with identical wavelength extending in opposite directions. The interference of two signals gives the resulting wave which, at first sight, does not move (that is standing).
Important condition is that energy has to come to a system with a certain speed. It means that the frequency of excitement has to be to approximately equal own frequency of fluctuations. Such concept is also known as a resonance. Standing waves are always connected with a resonance. Emergence of a resonance can be determined by sharp increase in amplitude of the resulting fluctuations. For creation of standing waves it is spent much less energy, in comparison with the running waves having the same amplitudes.
You should not forget also that in any system where there are standing waves, there are also numerous own frequencies. The variety of all possible standing waves is known as system harmonicas. The simplest of harmonicas is called fundamental or the first. The subsequent standing waves are called the second, third, etc. Harmonicas which differ from fundamental are called sometimes subtext.
Types of standing waves
Depending on physical characteristics there are several types of standing waves. All them can be divided into three big groups conditionally: one-dimensional, two-dimensional and three-dimensional. One-dimensional standing waves appear when there is a flat closed space. In this case the wave can extend only in one direction: from a source to space border. There are three subgroups of one-dimensional standing waves: with two nodes on the ends, with one knot in the middle and with a node on one of the ends of a wave. The node is a point with the smallest amplitude and energy of a signal. Two-dimensional standing waves arise in case fluctuations extend in two directions from a source. After reflection from a barrier there is a standing wave. Three-dimensional standing waves are the signals extending in space with a final speed. Knots at such type of fluctuations will represent two-dimensional surfaces. It considerably complicates their research. The orbit of the movement of an electron in atom can be an example of such waves.
Practical value of standing waves
Standing waves are of great importance in music as the sound is a combination of several fluctuations. The correct calculation of length and rigidity of strings allows to achieve the best sounding of any given tool. Standing waves are also very important in physics. In a method of a research of particles by means of x-ray spectroscopy the processing of the reflected signal allows to find out approximate quantitative and qualitative structure of an object.