The diffraction sound It is the property that waves have of flexing at the edges of obstacles or openings equal to or less than their wavelength and continuing to propagate. In doing so they are distorted and the smaller the opening through which they pass, the greater that distortion will be..
This property is easy to verify using a wave bucket, which consists of a tray filled with water and a source that generates the waves placed at one end. The source can be as simple as a vibrating metal band.
When the source is activated, a wave front is generated that moves in the tray and to which an obstacle can be interposed with an opening in the middle. The waves will manage to get around the opening and continue on their way, but their shape will have changed according to the size of the slit, to unfold once it is past..
The following image shows the same wavefront passing through two openings of different sizes..
When the aperture is reduced, the wave widens and curves appreciably. On the other hand, if the opening is larger, the deformation experienced by the wave is much smaller. The wave continues to advance, but it does not spread or unfold as much.
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The mentioned waves have been formed in the water of a simple tray. On a much larger scale, the diffraction of the waves around the islands of figure 1 can be seen, since the distance between them is of the order of their wavelength. This is key to understanding the phenomenon of diffraction..
As in the ocean, sound and light also experience diffraction, although of course light requires much smaller apertures, since the wavelengths of visible light are between 400 and 700 nanometers or trillionths of a meter..
For example, the tiny particles in the atmosphere act as obstacles for light to diffract, causing rings to be seen around very luminous objects such as light and the sun..
On the other hand, diffraction is facilitated by sound waves, since their wavelength is of the order of meters, so it is enough with openings the size of doors and windows for it to occur..
Diffraction is a unique property of waves. Let's imagine for a moment that instead of water it was a stream of marbles that passed through the openings.
The jet of marbles will continue to move in a straight line, instead of immediately dispersing throughout the available space, as waves do. Definitely, the material particles at the macroscopic level do not undergo diffraction, but the electrons, even having mass, can..
For this reason, all physical phenomena that are manifested through diffraction must be of the wave type. The other two characteristic properties are interference and polarization, with refraction and reflection equally applicable to particles of matter..
One person can talk to another even if there is a room in between and we can hear music and voices coming from other places, since the sound wavelengths are of comparable size or greater than everyday objects.
When you are in a room adjacent to another where music is playing, lower tones are heard better. It is because they have wavelengths longer than the acute ones, more or less the dimensions of doors and windows, so they have no problem in being diffracted in them, see the following figure.
Diffraction also allows people's voices to be heard before seeing them and bumping into them around the corner, since this is the obstacle that diffracts the waves.
Sound reflects off walls quite well too, so both properties combine to make sound bend corners quite well..
The sound of thunder in the distance makes it possible to distinguish the distant ones from the closer ones because the latter are perceived as crisp and dry, more like clicking and less rumbling, since the high frequencies (those of the highest sounds) are still present.
In contrast, distant thunder rumble and are more bass, thanks to the low frequencies with long wavelengths are able to evade obstacles and travel further. Higher components are lost along the way because their wavelength is smaller.
Surely you have noticed while driving through the city or through mountainous areas that the reception of some radio stations fades or loses quality to reappear later.
Radio waves can travel long distances, but they also experience diffraction when they meet buildings in the city or other obstacles such as hills and mountains..
Fortunately, thanks to diffraction, they can overcome these obstacles, especially if the wavelength is comparable to their size. The longer the wavelength, the more likely that the wave will be able to get around the obstacle and continue on its way.
According to the band it is in, one station may have better reception than another. It all depends on the wavelength, which is related to frequency and speed as:
c = λ.F
In this equation c is the velocity, λ is the wavelength and F is the frequency. Electromagnetic waves move at approximately 300,000 km / s the speed of light in vacuum.
So stations in the AM band whose frequencies are in the 525-1610 kHz range are more likely to experience diffraction than those in the FM range with 88-108 MHz..
A simple calculation with the above equation shows that AM wavelengths are between 186 and 571 m, while for FM stations, these wavelengths are between 2.8 and 3.4 m. The wavelengths of FM stations are closer to the size of obstacles such as buildings and mountains..
When light passes through a narrow slit, instead of seeing a whole uniformly illuminated region on the other side, what is seen is a characteristic pattern composed of a wider light central zone, flanked by dark bands alternating with light bands narrower.
In the laboratory, a very well-sharpened old-fashioned razor blade and a beam of monochromatic light from a laser allow this diffraction pattern to be appreciated, which can be analyzed with imaging software.
Light also experiences diffraction when it passes through multiple apertures. One device that is used to analyze the behavior of light in doing this is the diffraction grating, which consists of many equally spaced parallel slits..
The diffraction grating is used in atomic spectroscopy to analyze the light coming from atoms, and it is also the basis for creating holograms like those found on credit cards..
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