Sound
● Sound
○ It is a vibration that propagates as an audible wave of pressure, through a medium such as
solid, liquid or gas
○ It is measured in decibels (dB)
● These vibrations create sound. Waves which move through mediums such as air and water before
reaching our ears
● A vibration is a to and fro or back and forward motion
● Music is produced by periodic vibration having regular wave pattern
● Noise is produced by irregular vibrations having irregular wave pattern
● Longitudinal waves
○ When particles in a medium vibrate parallel to the direct of wave propagations in alternate
contractions and rarefactions are called longitudinal waves
○ Also called compressional or compression waves
○ They produce compressions and rarefaction while travelling
● Transverse waves
○ When particles of the medium vibrate perpendicular to the direction of wave propagation in
alternate crest and trough
○ Perpendicular to the direction of energy transfer
○ It can only travel through a solid since the particles move perpendicular to the wave, and so
must be attracted to the particles in order to affect them
Longitudinal waves
Transverse waves
Solid, liquid and gas
Only solids
Sound waves
Electro-magnetic waves
● Amplitude(A)
○ The maximum displacement of a wave. (height)
○ Its unit is metre (m)
● Wavelength (λ)
○ It is the distance between two consecutive crests or troughs of a wave
○ Its unit is metre
● Frequency(f)
○ The number of waves produced in one second
○ F = 1/time pause
○ Unit is hertz (Hz)
● Time pause
○ The time taken to produce one complete wave. Its unit is in seconds(s)
○ T = 1/frequency
● Speed(v)
○ Distance travelled by the wave in one second
○ Unit m/s
● Wave equation
○ Speed = wavelength/Time
○ Speed = wavelength x frequency
● Main characteristics of sound
○ Produced by vibrations
○ Sound requires a material medium for propagation.
● Factors affecting sound
○ Greater the temperature, the greater the speed of sound
○ Pressure does not affect speed of sound
○ Amplitude greater, loudness greater
○ Higher pitch, higher frequency
● Speed of sound in
○ Air → 330 m/s
○ Water → 1500 m/s
○ Steel → 6100 m/s
● Higher frequency = higher pitch
● Lower frequency = lower pitch
● Oscilloscope
○ The instrument which allows us to see the waves produced by sound
● Echo
○ Echo is the reflection of sound waves that arrives of the listener with a delay after the direct
sound
○ Speed of sound or echo → v = 2d/t (m/s)
■ d = distance
■ t = time interval between sound
■ v = speed of sound
○ A true echo is the single reflection of the sound source
● Range of hearing
○ Audible frequency
■ 20 Hz - 20,000 Hz
○ Infrasonic sound
■ Frequency of sound below 20 Hz
○ Ultrasonic sound
■ Frequency of sound above 20,000Hz
● Sonar
○ Sound navigation and ranging
● Wavefront (transverse)
○ Distance between 2 wave lengths
○ Crests or troughs
○ Perpendicular to the distance of wave propagation
● Wavefront (longitudinal)
○ Take line between compressions or rarefactions
○ This forms the wave fronts
