Measuring the Speed of Sound | Physics for GCSE/IGCSE - Year 11 PDF Download

Speed of Sound in Air

• Sound waves travel at a speed of about 340 m/s in air at room temperature.
• The speed of sound in air varies from 330 to 350 m/s.

Speed of Sound in Materials

• Sound travels at varying speeds in different materials:
  • Fastest in solids
  • Slowest in gases
• The following table illustrates the typical speeds of sound in various substances:
  

Measuring the Speed of Sound

• Various experiments help determine the speed of sound. Below are three methods along with the apparatus for each experiment.

Method 1: Measuring Sound Between Two Points

• Two individuals stand approximately 100 meters apart.
• The distance between them is measured using a trundle wheel.
• One person holds two wooden blocks, striking them above their head.
• The second person possesses a stopwatch, starting it upon seeing the blocks being struck and stopping it upon hearing the sound.
• This process is repeated multiple times to derive an average time.
• The speed of sound is then calculated using a specific equation.
  

Method 2: Using Echoes

• A person stands about 50 meters away from a wall (or cliff) using a trundle wheel to measure this distance.
• The person claps two wooden blocks together and listens for the echo.
• A second person has a stopwatch and starts timing when they hear one of the claps and stops timing when they hear the echo.
• The process is then repeated 20 times, and an average time is calculated.
• The distance traveled by the sound between each clap and echo will be 100 meters.
• The speed of sound can be calculated from this distance and the time using the equation provided.

Method 3: Using an Oscilloscope

• Two microphones are connected to an oscilloscope and placed about 5 meters apart using a tape measure to measure the distance.
• The oscilloscope is set up so that it triggers when the first microphone detects a sound, and the time base is adjusted so that the sound arriving at both microphones can be seen on the screen.
• Two wooden blocks are used to make a large clap next to the first microphone.
• The oscilloscope is then used to determine the time at which the clap reaches each microphone and the time difference between them.
• This process is repeated several times, and an average time difference is calculated.
• The speed can then be calculated using the provided equation.
  

Measuring Wave Speed in Water

• Ripples on water surfaces serve as a model for transverse waves.
  • Measurement of the speed of these water waves is achievable through this method.

• Opt for a calm, flat water surface like a lake or a swimming pool.
• Two individuals position themselves a few meters apart, using a tape measure to determine the distance.
• One person initiates the process by creating a ripple in the water.
• The second person, equipped with a stopwatch, times the ripple's journey to them.
• Repeat the experiment 10 times to calculate an average time value.
• The average time and distance are then employed to calculate the wave speed using a specific equation.