# Wave phenomena: what they are, examples, summary

All the wave phenomena existing in nature occur due to the propagation of different types of waves. Waves are very specific movements, characterized by pulses or successive pulses, in which there is, exclusively, the propagation of energy.

## Summary of wave phenomena

• Wave phenomena are composed of waves and are extremely important for the development of modern society.
• Waves are forms of energy propagation.
• Wave phenomena are characterized by wave propagation.
• The wave phenomena are:
• reflection: it is the property that is related to the fact that wave phenomena are reflected;
• diffraction: it is the property of wave phenomena to bypass obstacles;
• refraction: it is the property of changing the propagation speed of wave phenomena;
• polarization: is the characteristic of wave phenomena to be filtered out;
• resonance: it is when the oscillation frequency of a wave phenomenon coincides with the natural oscillation frequency of a physical system;
• dispersion: is the property of wave phenomena being combined, resulting in a change in the speed of the resulting wave;
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• interference: it is the property of undulatory phenomena that can be added or reduced.
• Sunlight and sound are examples of waves of different natures.

## What are wave phenomena?

The undulatory phenomena are those in which the physical principles behind its happening are the waves. It is important to highlight that, in nature, several phenomena can be characterized as undulatory.

For example, the sound we hear when a person speaks is a kind of wave. In this case, we hear because of the disturbance in the air molecules that propagate to our ear, in which we have a structure capable of receiving and recognizing this disturbance.

In the case of microwave, used for residential purposes, we have the creation and propagation of another type of wave, different from sound waves and characterized as an electromagnetic wave. We can see, in the two cases mentioned, that the types of waves and, therefore, the wave phenomena involved have different natures.

## What types of wave phenomena?

Still using the two wave phenomena mentioned and in a more specific way, we define the sound phenomenon as being a phenomenon of mechanical waves and the microwave as being a phenomenon of electromagnetic waves. But what is the difference between the two natures of these phenomena? In the first case, we have the presence of sound waves.

THEs sound waves necessarily need a means of propagation. This means that we can only hear, as the sound wave needs air to propagate its energy. In the second case, we have the occurrence of electromagnetic waves. These do not require material means for propagation.

In other words, electromagnetic waves travel in a vacuum. That's why sunlight can reach Earth. Of course, we cannot fail to mention the fact that electromagnetic waves also propagate in material media.

Waves, especially electromagnetic waves, which are transverse waves, have some important properties related to some phenomena suffered by them.

• Reflection: phenomenon in which waves are reflected.
• Refraction: is related to the change in the propagation speed of a wave when it changes from one propagation medium to another.
• Polarization: can be understood as a kind of filter for transverse waves. Polarization selects only one vibration direction among all vibration directions of a wave. This is done by means of a polarizer, which only lets vibrations through in one direction.
• Dispersal: related to the propagation speed of waves. In this case, several waves with different speeds generate a resultant wave. This means that the propagation speed of the resulting wave changes with its component waves.
• Diffraction: in it the waves go around and over objects, including holes. This can cause waves to widen or scatter when passing through such holes.
• Interference: happens when two or more waves propagating in space meet. In this case there will be an overlapping of waves, which will result in a resulting wave. In this context, we classify interference in two ways. The first, called constructive interference, is the situation in which the resulting wave amplitude is the sum of the amplitudes of the waves that compose it. The second, called destructive interference, is the situation in which the amplitude of the resulting wave is the difference in the amplitudes of the waves that compose it.
• Resonance: evidences the undulatory character of physical systems. In this context, systems that are oscillating receive excitations at frequencies that correspond to one of their natural oscillation frequencies. Thus, the system starts to oscillate with ever greater amplitudes.

See too: What is infrasound and ultrasound?

## Examples of wave phenomena

### a) Mechanical wave phenomena

In addition to the example of sound waves, we can mention here the waves formed on the surface of a lake when we throw a stone or any object. The wave motion of a skin of a percussion instrument it is also a mechanical wave phenomenon. Also, you have the waves on a rope when you do physical exercise. In addition to these, there are many other wave phenomena in nature that fit these characteristics, that is, in which there is the presence of mechanical waves.

### b) Electromagnetic wave phenomena

These are the phenomena characterized by the presence of electromagnetic waves. In addition to microwaves, we can mention the radio waves; you X ray, for performing diagnostic imaging tests; O infra-red, to have night vision; and the vast majority of phenomena involving sunlight, such as light refraction, light reflection and diffraction.

The highly advanced electronic circuits used for diagnostic imaging equipment, objects electronics and household appliances, also fit into this type of phenomenon because it is wave propagation electromagnetic. In addition, of course, to collaborating with the constant development of modern society and increasing people's quality of life.

In summary, all these phenomena, as already mentioned, are based on the presence of wave phenomena electromagnetic, characterized by the propagation of waves and, therefore, of energy, without the need for a material medium therefore.

Considering the highlighted phenomena caused by the waves, we have the following examples for each case:

• Reflection: we see an image when we stand in front of the mirror precisely because light, which is a transverse electromagnetic wave, is reflected.
• Refraction: as an example we have the case of sunlight. When it passes from air to water in a swimming pool, its propagation speed decreases. The result of this change is that a person outside the pool sees an object inside the pool in a distorted way.
• Polarization: we mention here the case of sunglasses. Good sunglass lenses work as light polarizers. This means that, when using them, your eyes will receive lower light intensities, as the other directions of light vibrations cannot go beyond the lens. This, in fact, justifies the high price of glasses made up of good sun lenses.
• Dispersal: a good example would be the dispersion of waves on the surface of a lake when a stone is thrown into it.
• Diffraction: The wireless internet signal is a good example of this phenomenon. It can be recognized by your cell phone when you are in your room, even with the modem in the living room, for example. Thus, the wireless signal is a transverse electromagnetic wave that goes around all the walls and doors in your house, reaching your bedroom.
• Interference: as an example we have the cases of cell phones, which, when they play near speakers or even computers, can emit a sort of hiss.
• Resonance: as an example we have soldiers marching on a bridge. Its gait frequencies can match the bridge's natural oscillation frequencies. In this case, the amplitude of the resulting wave grows more and more and the bridge structure may even break.

Read too: How is the rainbow formed?

## Wave phenomena in everyday life

In everyday life, wave phenomena are present all the time, from when we wake up and we can see objects through reflection, diffraction and refraction luminous, until the moment we go to sleep, with the our body's heat production under the cover.

Heat is also a mechanical wave phenomenon and, therefore, it needs a material medium for propagation. In addition to these and those mentioned throughout the text, there are a very large number of wave phenomena that fit all the characteristics mentioned.

## Solved exercises on wave phenomena

question 1 - (IFGO) Waves are ways of transferring energy from one region to another. There are mechanical waves — which need material means to propagate — and electromagnetic waves — which can propagate both in a vacuum and in some material media. About waves, we can correctly state that

A) the energy transferred by an electromagnetic wave is directly proportional to the frequency of that wave.

B) sound is a kind of electromagnetic wave and, therefore, it can be transmitted from one antenna to another, as in TV and radio transmissions.

C) visible light is a mechanical wave that only propagates transversally.

D) there are electromagnetic waves that are visible to human eyes, such as ultraviolet, infrared and microwaves.

E) Infrasound is an electromagnetic wave with a frequency below the audible one.

Resolution

Alternative A. Sound is a mechanical wave, not an electromagnetic one. Light is an electromagnetic, not a mechanical wave. Ultraviolet, infrared and microwave waves are not visible to the naked eye. Infrasound is a sound wave and therefore mechanical.

question 2 - (Fatec) Check the correct alternative.

A) Radio waves are mechanical waves.

B) Every transverse wave is electromagnetic.

C) In the reflection of a wave, its length and speed change, but its frequency is maintained.

D) When a wave passes from a more refracting medium to a less refracting one, there is a change in the wavelength, but not in its frequency.

E) A wave that propagates through a vacuum is a mechanical wave.

Resolution

Alternative D. The wave phenomenon characterized by the change of medium in which a wave propagates is called refraction. In it there is a change in wavelength and speed, but its frequency remains constant.

by Luiz Guilherme
Physics teacher

Source: Brazil School - https://brasilescola.uol.com.br/fisica/fenomenos-ondulatorios.htm

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