You Sound Funny - Answer

You Sound Funny - Answer = A

Although it is related to the density of the gas, the correct answer is A. By kinetic theory the kinetic energy of a gas is proportional to the temperature of the gas. (1/2mv2 = 3/2kT). Since helium is lighter than air, it will have a greater velocity at the same temperature. The next point is that our voice can be considered to be produced by resonating sound waves in the mouth and throat regions. In a resonating cavity the velocity of the sound wave equals the frequency times the wavelength of the sound wave (v = freq * wavelength). The wavelengths are basically fixed by the dimensions of the sound cavity (and are the same for air and helium), therefore if the velocity of the gas is larger and the wavelength does not change, the frequency must increase to satisfy the condition that v = freq * wavelength. This results in the higher pitch sound.

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