sound waves

• • sound waves are longitudinal waves
• how is sound produced?

  • vibration of particles in a medium (the substance the waves travel through)
  • the vibrations mean that the sound waves travel in a series of compressions and rarefractions
• compressions

  • where the medium is squashed together
• rarefractions

  • where the medium is stretched apart
• ears

  • detect vibrations and transfer information to our brain via auditory nerve
  • sensitive to a range of frequencies between 20Hz and 20,000Hz
• ultrasound

  • frequency above 20,000Hz
• sound is a wave

  • therefore, it can be reflected (e.g echoes), diffracted and refracted
• at a cricket match, why does the sound of the bat hitting the ball arrive at your ears after you see it happen?

  • speed of light is faster than speed of sound
  • light waves reach your eyes before sound wave reaches ears
• signal generators

  • sound waves can be created using a signal generator
  • oscilloscope can be used to observe wave
  • by connecting a signal generator to a loudspeaker, we can create and listen to sounds of different frequencies
  • oscilloscope can be used to measure amplitude and frequency of a sound wave
• oscilloscope traces

  • higher the frequency of sound wave, higher the pitch of sound
  • higher frequency means there’s shorter wavelength; shown on oscilloscope when peaks of waves are closer together
  • larger amplitude of sound wave, higher volume of sound
• measuring speed of sound - experiment:

  • two people stand a measured distance from tall, vertical wall - ideally 100m
  • first person bangs two wooden blocks together to make sharp sound, and repeats this everytime echo is heard
  • starting counting from zero, second person uses stopwatch to measure time taken for number of claps - 50 or 100
  • in time between two successive claps, the sound travels to wall and back