Waves

I. Sound cannot be polarized

The phenomenon of polarization consists of preventing the passage of transverse waves that have a certain direction of propagation through a filter called a polarizer. Note in the image below that the polarizer only allows waves to pass vertically, retaining waves with horizontal vibration.

Polarization only occurs with transverse waves, that is, waves that have a direction of propagation perpendicular to the vibration. Sound is a longitudinal wave and vibrates parallel to propagation, so it cannot be polarized .

II. There is a minimum distance required for echo to occur

Echo occurs when the sound wave emitted by a source is reflected by an obstacle and returns to the source, so that there is a distinction between the emitted and reflected sound. The human ear can only distinguish two sounds if they reach the hearing aid within a minimum interval of 0.1 s. This time is called sound persistence . Knowing that the speed of sound in air, considering normal conditions of temperature and pressure, is 340 m/s, we can determine the minimum distance between the source and the obstacle that will reflect the sound.

Knowing that velocity is defined as the ratio between the distance traveled by a mobile (ΔS) and the time spent (Δt), we can write:

v = ΔS ÷ Δt

Bearing in mind that the sound must leave the source, collide with the obstacle and return to the source, we must double the space:

v = 2. ΔS ÷ Δt

v. Δt = 2. ΔS

340 0.1 = 2. ΔS

34 = 2. ΔS

ΔS = 17 m

We conclude that, for the occurrence of the echo, the obstacle that will reflect the sound must be at least 17 m from the emitting source.

III. Frequency does not change in refraction

Refraction occurs when a wave changes its propagation medium. In the event of this phenomenon, there will always be an increase or decrease in wave speed . The product of frequency (f) and wavelength (λ) determines the speed of a wave. As in the refraction there will be a change in velocity, the product f.λ will also be changed. It is important to emphasize that, as the frequency is a characteristic maintained by the source generating the waves, it is not changed. Therefore, we can say that, in refraction, only the wavelength (λ) is modified.

IV. Sound is faster on solids

Sound is a mechanical wave, that is, it needs a propagation medium . Therefore, the greater the proximity between the molecules that make up the medium, the greater the ease of propagation of sound and the greater its speed. We can therefore conclude that the speed of sound in solids is greater than in liquids and gases. Taking V as the speed of sound, we can write: V _SOLIDS > V _LIQUIDS > V _GASES .

V. Blue is the hottest color!

The energy associated with electromagnetic radiation is related to its frequency of oscillation. The radiations with greater frequency have greater associated energy. Through the electromagnetic spectrum , we can see that the blue, indigo and violet colors of visible light have frequencies higher than the red and orange colors, therefore, the radiations in bluish tones emit more energy.

The idea that blue represents cold and that red represents hot is established daily because the notion of hot and cold colors tells us that the colors related to fire are the warm ones. This idea, valid from an artistic point of view, must be disregarded in a scientific analysis.