Sound Waves Test Physics

• Sound Waves are longitudinal waves which can be reflected and refracted
• The frequency range for a human is 20-20000 Hz
• An oscilloscope displays sound waves
• How does an oscilloscope and microphone be used to display sound waves?

  1. A sound receiver, such as a microphone can pickup sounds travelling through air.
  2. To display these sound waves, and measure their properties, you can plug the microphone into an oscilloscope. The microphone converts sound to electrical signals.
  3. An oscilloscope is a device that shows microphone signals as a trace on a screen.
  4. The wave tells you if it is loud or quiet, high pitch or low pitch.
• The higher the pitch, the higher the frequency
• Frequency is the number of complete vibrations, measured in Hz. 1Hz = 1 vibration. Other units KHz (1000), MHz (1000000 Hz)
• The more complete cycles displayed on the oscilloscope - the more complete cycles displayed
• Loudness increases with Amplitude
• The greater the amplitude of a wave the more energy it carries. in sound this means it’ll be louder. Louder sound waves will also have a trace with a larger amplitude on an oscilloscope.
• What formula do you use to work out the speed of sound in air?

  speed=distance/time
• Investigate the frequency of a sound wave using an oscilloscope

  1. Connect the microphone to the oscilloscope

  2. Check that waveforms are produced when sounds are made

  3. Alter the oscilloscope settings to ensure that the wave forms fill the screen and are clear
• Measure the frequency of a sound wave

  1. Make a sound using an instrument or by humming a note

  2. Press the hold button on the oscilloscope so that the wave-form produced is frozen

  3. Measure the distance between two peaks

  4. Refer to the time base to calculate the length of time between the peaks
• Time period


  The time taken for one wave to be produced
• Calculate the frequency of the wave


  Use the formula: f = 1/T
• Speed of sound in air practical

  1. Measure the distance from one side of the open space to the other side using a trundle wheel or long tape measure, marking with a marker the start and end point of your measurement

  2. One of your pair should stand at one marker with the wooden blocks, and the other should stand at the other marker with a stopwatch

  3. Once both ready, the block holder should strike the two blocks together

  4. At the instant they see the blocks touch, the other person should start the stopwatch

  5. At the instant they hear the sound, they should stop the stopwatch

  6. This should be repeated 10 times

  7. The speed should be calculated using: Speed = distance / time

  8. An average speed for all repeats should be calculated