# Sound Waves in Different Mediums

1. May 20, 2017

### Joseph Phan

1. The problem statement, all variables and given/known data
1) When sound waves travel through increasing temperature, what increases, frequency, wavelength, or both?
2) When you inhale helium and then your voice becomes high and squeaky, what causes this to happen?

2. Relevant equations
Vsnd= √(γRT/ M)
vsnd= λf

3. The attempt at a solution
I know that in both # 1 and 2, the speed of sound increases, but I'm fixated on the concept that when sound travels through different mediums, such as from air to water, the frequency stays the same, but the wavelength changes.

For #1, Temperature increases, which increases the velocity of the molecules in air, so I'm assuming that the frequency increases as the number of oscillations/s increases. However, does the wavelength change?

For #2, I'm confused on how frequency(pitch) changes, if the medium is changed. From the recent concept in that the frequency of sound does not change from one medium to another and that the speed of sound increases in He than in air, because He is less dense than air, how does your voice get higher as you inhale helium?

Last edited: May 20, 2017
2. May 20, 2017

### kuruman

Where did you get this? What do symbols T and σ represent?

3. May 20, 2017

### Joseph Phan

My professor used different greek notations, I think what he meant was that velocity of sound was proportional to the square root of abs. temperature over inertia

4. May 20, 2017

### kuruman

Model the sources of sound in (1) and (2) as being strings vibrating at their fundamental frequency. Vocal chords are strings. Write an expression for the fundamental frequency in terms of the length of the strings and the speed of sound. Study the expression and consider what happens to the frequency when the speed of sound changes.