# Use an oscilloscope to measure the speed of sound

By attaching a signal generator to a speaker you can generate sounds with a specific frequency. You can use two microphones and an oscilloscope to find the wavelength of the sound waves generated

• Set up the oscilloscope so the detected waves at each microphones are shown as separate waves

• Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart

• Measure the distance between the microphones to find one wavelength

• You can then use the formula v=fa to find the speed of the sound waves passing through the air- the frequency is whatever you set the signal generator to

• The speed of sound in air is around 330m/s, so check your results roughly agree with this

# Measure the speed of water ripples using a lamp

• Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency

• Use a lamp to see wave crests on a screen below the tank. Make sure the size of the waves’ shadows are the same size as the waves

• The distance between each shadow line is equal to one wavelength. Measure the distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find the average wavelength. This is a good method for measuring small wavelengths

• If you’re struggling to measure the distance, you could take a photo of the shadows and ruler, and find the wavelength from the photo instead

• Use v=fa to calculate the wave speed of the waves

• This set-up is suitable for investigating waves because it allows you to measure the wavelength without disturbing the waves

# You can use the wave equation for waves on strings

• Set up the equipment shown on the right, then turn on the signal generator and vibration transducer. The string will start to vibrate

• Adjust the frequency of the signal generator until there’s a clear wave on the string. The frequency you need will depend on the length of string between the pulley and the transducer, and the masses you’ve used

• You need to measure the wavelength of these waves. The best way to do this accurately is to measure the lengths of, say four of five half-wavelengths in one go, then divide to get the mean half-wavelength. You can then double this mean to get a full wavelength

• The frequency of the wave is whatever the signal generator is set to

• You can find the speed of the wave using v=fa