Study Material

Wave diffraction: concept and examples

We explain the wave diffraction with concept and examples. The diffraction waves is the deviation of the direction in which the waves propagate when they encounter an obstacle, which may be a solid object or a gap.Â When hitting the obstacle, the wave is distorted and surrounds it.Â But for the effect to be well appreciated, it is necessary that the size of the obstacle is comparable to that of the wavelength. Wave diffraction

The phenomenon of wave diffraction is explained according to the Huygens principle, discovered by the Dutch physicist Christian Huygens in 1678. It is stated that when the disturbance reaches a medium, each point of it behaves as an emitter of new waves, of the same speed and frequency as the original ones.

In this way, a new wavefront is continuously produced, which can be visualized by tracing the envelope of each emitted secondary wave. Wave diffraction

Naturally, this wavefront has infinite points, but precisely in the place of the obstacle there is a single wavefront that acts as an emitter, which makes it possible for the wave to bypass the obstacle, bend and propagate to the other side. Wave diffraction

Examples of wave diffraction Wave diffraction

Diffraction is a characteristic phenomenon of all waves, including light and acoustic waves.Â If a jet of particles is fired towards an apertured screen, the jet does not behave in the same way as a wave such as light would, for example, since the stream of particles would not be deformed to be bent by the obstacle or the intervening opening, but would continue in a straight line.

The first to experience and document the phenomenon of diffraction of light was the Italian scientist and priest Francesco MarÃ­a Grimaldi (1618-1663), and also the one who gave it his name. Wave diffraction

Project sunlight into a dark room

A the like did Grimaldi, it can be seen that by passing the light from the sun inside a dark room and projecting on the wall through a provided cardboard of a small hole or slot, the light spot is larger to the expected. Wave diffraction

It can also be seen that the edges are not sharp and although it is not that simple to observe, the edges in the shadow have a diffuse fringe pattern.Â But if monochromatic light is used, such as that from a laser, there is a more pronounced stripe pattern.

The diffraction of light is not as evident as that of sound or ocean waves, because for it to occur, the obstacle or opening must have a length comparable to that of the wavelength.Â Visible light has wavelengths between 400-700 nanometers (1 nanometer = 10Â -9Â meters).

Therefore, the narrower the slit through which the light that is projected on the wall or screen is allowed to pass, it is more evident that there is no abrupt change between the illuminated area and the dark area.

The electron microscope Wave diffraction

Diffraction of light is a limitation for the light microscope.Â When an object is smaller than the wavelength of light there is no way to see it, because diffraction completely blurs the image of the object.

This is why scientists use electrons to illuminate very small structures, since the wavelength of an electron beam is shorter than that of light.Â It happens that electrons have a dual nature and are capable of behaving like waves.

Diffraction of sea waves Wave diffraction

The diffraction of marine waves is clearly seen around rocks and small islands, especially when the distance between these rocks is very similar to the wavelength of the waves.

X-ray diffraction Wave diffraction

Diffraction does not only occur with visible light, but also with the rest of the electromagnetic spectrum.Â By interposing a crystalline structure before an X-ray beam, the diffraction they experience produces a pattern that depends on that structure.

This diffraction is due to the interaction between the X-rays and the outer electrons of the crystal atoms.

Animal communication

Many animals communicate with each other by emitting sounds that, due to their low frequency, are inaudible to humans.Â The audible range of people is very wide, oscillating between 20 and 20,000 Hz, but animals such as the African elephant are capable of emitting sounds with frequencies below 20 Hz.

The phenomenon helps them to communicate across the vast African savannas, as the lower the frequency, the more easily acoustic waves are diffracted.Â When they meet rocks, trees and bushes, one part is reflected in the obstacle and the other expands past the obstacle and immediately filling the medium as it passes.

This helps pack members to easily locate each other.

But not only pachyderms make use of this property of sound, rhinos, giraffes and crocodiles are also capable of using low-frequency sounds.Â Even the roar of tigers contains low frequencies, which experts say contribute to paralyzing prey.

Fog horns Wave diffraction

They are speakers that serve to guide boats in areas where fog prevents good visibility. Likewise, boats have these horns to warn of their presence and thus avoid accidents. Wave diffraction

Fog horns emit low-frequency sounds, that is, low notes, since as explained above, low-frequency sounds are diffracted more than high-frequency sounds, and also travel greater distances.

The latter is due to the fact that the attenuation of the sound wave is lower the lower the frequency.Â For this reason, high-pitched sounds are lost faster than bass, another reason why elephants use very low-frequency sounds to communicate.