PAG: Measuring Wave Properties

• PAG: Measuring Wave Properties

  Equipment List

  
• • Resolution of measuring equipment:
  • Metre ruler = 1 mm
  • Stopwatch = 0.01 s
• Aims of the Experiment

  • To measure frequency, wavelength and wave speed by observing water waves in a ripple tank

  Variables

  • Independent variable = frequency, f
  • Dependent variable = wavelength, λ
  • Control variables:
  • Same depth of water
  • Same temperature of water
• Method: wave property

  
• Set up of ripple tank to investigate wave properties

  1. Set up the apparatus as shown and fill the ripple tank with water to a depth of no more than 1 cm
  2. Turn on the power supply and the light source to produce a wave pattern on the screen
  3. The wavelength of the waves can be determined by using a ruler to measure the length of the screen and dividing this distance by the number of wavefronts
  4. The frequency can be determined by timing how long it takes for a given number of waves to pass a particular point and dividing the number of wavefronts by the time taken
• Set up of ripple tank to investigate wave properties

  1. Record the frequency and wavelength in a table and repeat the measurements
• • An example of the data collection table is shown below:

  
• Analysis of Results

  • The speed of the waves can be determined using the equation:

  Wave Speed = Frequency × Wavelength

  v = fλ

  • Where:
  • v = wave speed in metres per second (m/s)
  • f = frequency in Hertz (Hz)
  • λ = wavelength in metres (m)
• Evaluating the Experiment

  Systematic Errors:

  • It can be difficult to identify the wavefronts while they are moving
  • Use a stroboscope (flashing light) matched to the same frequency of the waves, this will be indicated by the waves appearing to be stationary
  • The frequency can be read from the frequency setting of the stroboscope, and the wavelength will be easier to determine while the waves appear still
• Evaluating the Experiment

  Random Errors:

  • To improve the accuracy of the wavelength measurement in the ripple tank:
  • Measure across a number of waves (e.g. 5 of them) and then divide the distance by the number of waves
  • To improve the accuracy of the frequency measurement in the ripple tank:
  • Measure across a longer time period (e.g. a minute) and then divide the number of waves by the time
• Safety Considerations

  • Care should be taken when working with water and electricity in close proximity
  • Carelessness could lead to electric shock
  • Make sure to stand up during the whole experiment, to react quickly to any spills
  • No food or drink should be consumed near the experiment 
  • If using strobe lighting to see the wavefronts more clearly, ensure no one in the room has photosensitive epilepsy