Sound and Oscillation

# wave phenomena

The wave phenomena are behaviors that waves have when they propagate and bump into different obstacles, surfaces or media.

The wave phenomena refer to the specific behavior of waves when they encounter an obstacle, surface or medium different from what it was before. They occur for any type of wave , but it is more common to study with visible light waves. The seven most common types of wave phenomena are:

• reflection,
• refraction,
• polarization,
• dispersal,
• diffraction,
• interference and
• resonance.

• Wave phenomena are behaviors that waves have when bumping into obstacles or changing mediums.
• These phenomena occur with any type of wave: mechanical or electromagnetic.
• The seven types of wave phenomena are: reflection, refraction, polarization, dispersion, diffraction, interference and resonance.

## What are wave phenomena?

Wave phenomena occur with waves when they change medium or when they bump into objects along their path. These behaviors are independent of the nature of the wave.

## Types of wave phenomena

Basically, there are seven types of behaviors that a wave can acquire, that is, seven phenomena: reflection, refraction, polarization, dispersion, diffraction, interference and resonance.

• ### Reflection

Reflection occurs when the wave bumps into a solid object and returns to the same medium. In this situation, its speed, frequency, and length remain the same. Furthermore, by virtue of the first law of reflection, we know that the angle of incident waves is the same as that of reflecting waves.

There are two types of wave reflection: specular or regular and diffuse.

In specular/regular reflection, the reflective surface is extremely polished. Thus, the reflection is organized and the formation of images is possible . In diffuse reflection , the surface has roughness, causing the reflected rays to go to different points, not allowing the formation of clear images .

• ### Refraction

Refraction occurs when the wave passes through a different medium and is deflected . Each medium has a different difficulty of passing the wave. More difficult media (such as glass) have higher refractive indices (N) than media through which the wave passes more easily (such as air).

As the medium changes, its speed, direction and wavelength change, but its frequency remains the same (as it only depends on the source that emits the wave). By means of the Snell -Descartes law , it is possible to find the angles of incidence and refraction that are different.

• ### Polarization

Polarization occurs when the wave is oriented in only one direction . This occurs when the wave (which can be in several directions) passes through a polarizer and begins to vibrate in the same direction as the polarizer.

Only transverse waves (which have the propagation direction different from the vibration direction) can be polarized, due to the amplitude variation.

• ### Dispersal

Scattering happens with light waves, as when white light is split into other color beams when bumping into objects such as glass cousins.

• ### Diffraction

Diffraction occurs when the wave encounters an obstacle and is able to propagate through an opening or around the obstacle

Although the wave manages to pass through the obstacle, the wave’s energy is lost in the process .

• ### Interference

Interference occurs when a wave bumps into another wave. There are two types of interference: constructive and destructive.

In constructive interference , waves with the same phase combine to form a wave of greater amplitude. In destructive interference , waves with different phases and close frequencies subtract, canceling each other out.

• ### Resonance

Resonance occurs when an external wave has the same vibration as the vibration of some other body . In this situation the external vibration is absorbed by the internal one and thus the natural vibration is amplified.

## Wave phenomena in everyday life

Wave phenomena are occurring all the time in our world. Human beings were able to study and apply them to facilitate processes in our daily lives. See some examples below:

• Extremely polished objects generate regular reflection, like mirrors.
• We see the effect of refraction when placing objects in different media such as air and water.
• In sunglasses, the polarization effect is used to reduce the amount of electromagnetic radiation that reaches our eyes.
• An example of a phenomenon where we can find dispersion is the formation of a rainbow , which occurs when white light from the Sun undergoes reflection and refraction in water droplets and is dispersed.
• Due to resonance, we have equipment capable of recording images, as in magnetic resonance imaging :
• Diffraction can be perceived when we hear something, even if it came from another environment.
• Interference occurs a lot in telecommunications, causing noise or image interference.

## Solved exercises on wave phenomena

Question 1 – (Enem 2013) When traveling by plane, passengers are asked to turn off all devices whose operation involves the emission or reception of electromagnetic waves. The procedure is used to eliminate sources of radiation that could interfere with the pilots’ radio communications with the control tower.

The property of the emitted waves that justifies the procedure adopted is the fact that:

A) have opposite phases.

B) both are audible.

C) have inverse intensities.

D) be of the same amplitude.

E) have similar frequencies.

Resolution

Alternative E. Wave interference between electronic devices is mainly due to the proximity of wave frequencies. For this reason, it is necessary to turn off cell phones so that the electromagnetic waves of these devices, which are close to the radio waves of communication equipment, are not affected.

Question 2 – (UFRGS 2013) Mark the alternative that correctly fills in the gaps in the text below, in the order in which they appear.

The light radiation emitted by a lithium vapor lamp passes through a block of transparent glass, with a refractive index greater than that of air. When penetrating the glass block, light radiation has its frequency _________ . The wavelength of radiation in the block is _________ than in air and its propagation speed is _________ than in air.

A) altered – major – minor.

B) altered – same – greater.

C) unchanged – major – minor.

D) unchanged – minor – minor

E) unchanged – smaller – the table.

Resolution

Alternative D. The condition for changing the frequency of a wave is for the source to change the emission. When light passes through a medium that has more resistance, the index of refraction is higher and, therefore, it has more difficulty to pass, thus decreasing its wavelength and speed.