Section 3: Waves
KS3 Connections:
Exploring Science 7, 8 & 9 


a) Units
b) Properties of waves
Students will be assessed on their ability to:
3.1 use the following units: 
degree (o)                    angles
hertz (Hz)                     frequency, how many cycles per second
metre (m)                     distance
metre/second (m/s)    velocity 
second (s).                    time
3.26 understand that sound waves are longitudinal waves and how they can be reflected, refracted and diffracted
 
​Sound waves vibrate particles and can be generated from speakers or tuning forks etc. 
 They are longitudinal waves, the vibrations are parallel to the direction.
 Speed of sound is approximately:
                                          330m/s in air (depends on temperature and pressure                                       
                                          1500m/s in seawater (particles closer together compared to air)
                                           5000m/s in concrete (particles even closer together compared to liquid and gas)

​Like all other waves sound waves can be reflected (echo), diffracted and refracted.
          diffracted    (also sound through a doorway)                                            refracted     at night hot air rises(bottom diagram)
3.27 understand that the frequency range for human hearing is 20 Hz – 20 000 Hz
                       You need to know human audible range  20 - 20000HZ
3.28 describe an experiment to measure the speed of sound in air
  • Someone stands a measured distance away (100m) and fires a starter pistol or hits two symbols.
  • Use a stopwatch to start the time from when you see them fire the pistol (from the smoke) or hit the symbols
  • Stop the watch when you hear the sound.
  • You will need to repeat this, 5 - 10 times and take the average reading, this will cut down some inaccuricies.
  • Using v =d / t you can work out the speed of sound. 
  • This is inaccurate due to your reaction time (about 0.1ms).
  • You will need to do the experiment in still air.

  • You can stand 50m from a wall
  • set up a rhythm of claps so that the echo comes exactly between two claps.
  • Ask a friend to time 20 claps. 
  • During this time the wave will have travelled (50 x 2) x 20 = 2000m. (to the wall and back x 20). 
  • Now divide the distance by the time.
3.29 understand how an oscilloscope and microphone can be used to display a sound wave
Connect a microphone to an oscilloscope to produce a trace.
​Sound waves from a speaker are converted to electrical signals using a microphone. 
The oscilloscope shows these electrical signals as waves on the screen.
3.30 describe an experiment using an oscilloscope to determine the frequency of a sound wave

                                                         Time period = 5 x 3 = 15s                Time period = 5 x 0.005 = 0.025s
                                                      frequency = 1 / Time period               frequency = 1 / Time period        
                                                        frequency = 1 / 15 = 0.07hz              frequency = 1 / 0.025 = 40hz
3.31 relate the pitch of a sound to the frequency of vibration of the source
3.32 relate the loudness of a sound to the amplitude of the vibration