Measuring the Speed of Waves (AQA GCSE Physics Combined Science): Revision Notes

Sound in Air

• Method 1:
• Make a noise at ~50m from a solid wall
• Record the time for the echo to be heard
• Use the formula: speed = distance/time
• Method 2:
• Use two microphones connected to a datalogger at a large distance apart
• Record the time difference between a sound passing from one to the other
• Use the formula: speed = distance/time

Ripples on Water Surface

• Method 1:
• Use a stroboscope with the same frequency as the water waves
• Measure the distance between the 'fixed' ripples
• Use the formula: $v = f \lambda$
• $v$ is the wave speed in metres per second (m/s)
• $f$ is the frequency in hertz (Hz)
• $\lambda$ is the wavelength in metres (m)
• Method 2:
• Move a pencil along the paper at the same speed as a wavefront
• Measure the time taken to draw this line
• Use the formula: speed = distance/time