Sound Waves (DP IB Physics: HL): Revision Note

Sound Waves

• Sound waves are longitudinal waves and, as such, require a medium in which to propagate

• Sound waves are generated by oscillating sources, which produce a change in density of the surrounding medium

• The sound wave then travels with a series of compressions and rarefactions

A sound wave travelling through air

• Sound waves form a continuous spectrum based on their frequency

The spectrum of sound waves

• Humans can only hear sounds with frequencies in the range 20 Hz - 20 kHz, known as the audible range 

• Sounds with frequencies below and above this range cannot be detected by the human ear

Pitch & Volume

• The frequency of a sound wave is related to its pitch

  • Sounds with a high pitch have a high frequency (or short wavelength)

  • Sounds with a low pitch have a low frequency (or long wavelength)

• The amplitude of a sound wave is related to its volume

  • Sounds with a large amplitude have a high volume

  • Sounds with a small amplitude have a low volume

Pitch and amplitude of sound

Speed of Sound

• Sound waves travel at a speed of about 340 m s^–1 in air at room temperature

  • The higher the air temperature, the greater the speed of sound

  • The is because the average kinetic energy of the particles is higher

• Sound travels the fastest through solids, since solid particles are closely packed and can pass the oscillations onto their neighbours much faster

• Sound travels the slowest in gases, since gas particles are spread out and less efficient in transferring the oscillations to their neighbours