Wavelength
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- For a transverse wave, the wavelength is the distance between two successive crests or troughs.
- For a longitudinal wave, it is the shortest distance between two peak compressions.
Amplitude
- The amplitude of a sound wave is the degree of motion of air molecules within the wave.
- This corresponds to the extent of rarefaction and compression that accompanies the wave.
- The greater the amplitude of the wave, the harder the molecules strike the ear drum and the louder the sound is transduced.
- The amplitude of a sound wave can be expressed in absolute units by measuring the actual distance moved by the air molecules, or the pressure difference in the compression and rarefaction, or the energy involved.
- Eg. Ordinary speech produces sound energy at a power level of about one hundred-thousandths of a watt (10⁻⁵W = 10µW)
Velocity
- The velocity of the wave, which is the speed at which it advances, is equal to the wavelength times the frequency.
- The frequency of the wave is the number of vibrations (complete cycles) per second. The unit is the Hertz (Hz).
- Velocity (m/s) = wavelength (m) x frequency (Hz)
v = ƛ x f m/s
So if 1kHz tone in air has a wavelength:ƛ = v/f m
= 333/1000 m
= 0.333 m
which is slightly longer than a 12" ruler.
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