The human voice is produced in the larynx, resulting from the passage of air that comes from the lungs during exhalation, causing vibrations in the vocal folds and generating sound. Thus, our vocal folds vibrate forming waves that need a means of propagation. Generally, this medium is the air itself, which is made up of approximately 78% nitrogen gas (N2). Thus, the nitrogen molecules are compressed and move up and down, creating the sound wave.
Waves are characterized by their wavelength (λ), which is the distance between one crest and another or between one depression and another, and by its frequency (f), which are the wave oscillations, that is, the number of crests (or troughs) that pass through a point within one second. The unit of wave frequency is hertz (Hz), where 1 Hz equals 1 cycle per second.
The wavelength is the distance from one peak to another of an electromagnetic wave.
The propagation speed of these sound waves then depends on the propagation medium. Helium is a very light gas, its atomic mass is 4 u and, therefore, it is used in party balloons that rise through the air.
Helium is therefore much lighter than nitrogen, the latter having a mass seven times greater. The propagation speed of helium is 965 m/s, that is, three times greater than the propagation of atmospheric air. Thus, when helium is inhaled, sound travels much faster, sound waves have a frequency and propagation speed much higher than normal, and the voice acquires a finer timbre than the normal.
The voice becomes thin by inhaling helium gas because the speed of sound waves increases
Similarly, if we inhale a denser gas, the voice will travel at a slower rate and will thicken.
But it is important to remember: it is not recommended to carry out this type of experiment, as like helium gas, many gases can cause suffocation. Also, by inhaling helium gas, you cut off the flow of oxygen to the brain, which can lead to death.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/por-que-gas-helio-afina-voz.htm
