waves

• Ripple tank

  A shallow tray of water with a vibrating bar that creates waves across the surface of the water
• Ripple tank

  • Has a lump on below the tank and a sheet of white paper, when light shines through the water it produces an image of the waves on the paper
• Measuring wavelength

  Place a ruler on the paper, freeze the image of the waves, measure the distance between one wave and 10 waves, divide by 10 to find one wavelength
• Measuring frequency

  Place a timer next to the paper, count the number of waves passing a point in 10 seconds, divide by 10 to find the frequency in Hertz
• Measuring wave speed

  1. Use the wave equation: wave speed = frequency in Hertz x wavelength in meters

  2. Select a wave and measure the time it takes to move the length of the tank, divide distance by time
• Measuring wave speed using the two methods may give slightly different results due to measurement errors
• This is a required practical, so the details need to be learned
• Wavelength


  The distance between two consecutive peaks or troughs of a wave
• Frequency


  The number of wave cycles that pass a given point per unit of time
• Wave speed


  The speed at which the wave propagates through the medium
• Measuring wavelength, frequency and speed of waves in a solid


  1. Set up apparatus with string, vibration generator, and hanging mass

  2. Adjust signal generator to create standing wave

  3. Measure total length of standing wave

  4. Calculate wavelength by dividing total length by number of half-wavelengths and multiplying by 2

  5. Read frequency from signal generator

  6. Calculate wave speed using wave equation: wave speed = frequency x wavelength
• In the exam, students will not be required to explain how standing waves or resonance happen
• Standing waves found in


  • Stringed musical instruments (e.g. guitar)
• Increasing frequency of standing wave

  Changes standing wave pattern to have more half-wavelengths
• Wave speed does not depend on frequency or wavelength, but on the tautness of the string and mass per unit length