Inhaling helium raises vocal pitch because sound travels faster in lighter gases
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Reference literature confirms that the speed of sound increases in gases with lower molecular weights, which explains why inhaling helium results in a higher vocal pitch.
gas; the relationship between the velocity of the particles of a gas and the speed of sound in that gas
Demonstration
- Listen to the results of different gases in an organ pipe. Observations
The different gases provide different pitches in the same pipe. Explanation
The velocity of sound in a gas is proportional to the ratio of the specific heats at constant pressure and constant volume (g) and the molecular weight (M). U = (gRT/M)1/2
Assuming that g is reasonably constant (it ranges from 1.15 to 1.66 for common gases), the speed of sound should increase as the molecular weight of the gas decreases. Since the product of the wavelength times the frequency of a wave is equal to the speed of the wave, and the "wavelength" of the organ pipe is more or less constant, the frequency of the wave must increase as the velocity of sound increases. This same phenomenon explains why one's voice becomes substantially higher after one inhales a quantity of helium. This can be done in class, but caution should be taken, as helium can act as an anaesthetic and/or an asphyxiant. Although hydrogen gas would produce an even higher pitched voice, it is not recommended for obvious safety concerns.
Because helium was previously very expensive only available from natural gas reserves in U.S., Nazi Germany had only hydrogen gas at its disposal. The consequences were devastating, as shown below:
Currently, helium is found in other natural gas reserves around the world. The cost of helium has decreased from $2500/ft3 in 1915 to $0.15/ft3 in 1989. Helium is what keeps the Goodyear blimps afloat over stadiums. Helium is often inhaled from balloons to produce a high, squeaky voice. This practice can be very harmful. Inhaling helium can lead to loss of consciousness and cerebral arterial gas embolism, which can temporarily lead to complete blindness. This occurs when blood vessels in the lungs rupture, allowing the gas to gain access to the pulmonary vasculature and subsequently the brain. Characteristics
Gas and plasma phases
Helium is naturally found in the gas state. Helium is the second least reactive element and noble gas (after neon). Its low atomic mass, thermal conductivity, specific heat, and sound speed are greatest after hydrogen.
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