4️⃣ 4 - speed of sound waves

Question 1

Sound waves in air are a type of __ wave

The speed of sound can be measured

Answer 1

Sound waves in air are a type of longitudinal wave

The speed of sound can be measured

Question 2

Method 1: Measuring Sound Between Two Points - 2 people

Answer 2

Two people stand a distance of around 100 m apart
The distance between them is measured using a trundle wheel
One person has two wooden blocks, which they bang together above their head
The second person has a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound
This is then repeated several times and an average value is taken for the time
The speed of sound can then be calculated using the equation: Distance travelled by sound / time taken

Question 3

Method 2: using echoes

Answer 3

A person stands about 50 m 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
The person then starts to clap the blocks together repeatedly, in rhythm with the echoes
A second person has a stopwatch and starts timing when they hear one of the claps and stops timing 20 claps later
The process is then repeated and an average time calculated
The distance travelled by the sound between each clap and echo will be (2 × 50) m
The total distance travelled by sound during the 20 claps will be (20 × 2 × 50) m
The speed of sound can be calculated from this distance and the time using the equation:

2 x distance to the wall / time taken

Question 4

Method 3: Using an Oscilloscope

Answer 4

Two microphones are connected to an oscilloscope and placed about 5 m 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 is repeated several times and an average time difference calculated
The speed can then be calculated using the equation:

Distance between microphones / time between peaks