Loading document…
Opening in Pages for Mac...
Your browser isn’t fully supported.
For the best Pages for iCloud experience, use a supported browser.
Learn More
Cancel
Continue
4.2 Travelling waves
4. Oscillations and waves
Measuring the speed of sound using toilet rolls
Background
“
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates
through an elastic medium. At 20 °C, the speed of sound in air is about 343 metres per second.
”
Source
:
https://en.wikipedia.org/wiki/Speed_of_sound
Equipment: three toilet rolls, wired headphones, ruler, blutack/post-it note/board pen.
Method
1.
Place toilet roll on a flat surface with one headphone at the bottom of the tube.
2.
Stack two more roll on top to make a tunnel for the sound and isolate external sounds.
3.
Stick some blutack on the other headphone to make it heaver and the wire taut.
4.
Search YouTube for ‘3 kHz test tone’ and play the sound through the headphones.
5.
Lower the second headphone to the bottom of the tube and slowly raise it.
6.
At a certain point the sound will be minimised. It will take a little tweaking.
7.
Mark the cable at the top of the tube then slowly raise the headphone until you hear the sound
disappear again. Mark this point.
8.
Remove the headphone and record the distance between the two marks. This is the
wavelength of the 3 kHz sound wave. Repeat at other frequency values.
Table of results
Analysis
Frequency / Hz
(1/frequency) / s
Trial 1
Trial 2
Trial 3
Average
Range / m
Uncertainty / m
1000
0.00100
2000
0.00050
3000
0.00033
4000
0.00025
5000
0.00020
Wavelength / m
4.2 Travelling waves
4. Oscillations and waves
We can linearise the date. This is much easier as we now know the relationship between the two
variables using the wave speed equation. We know we can plot 1/f against λ with the gradient
being the wave speed. In this case it is the speed of sound.
Calculate the gradient of the line and hence the speed of sound. Annotate the graph to show your
working and include units.
Explain how we could determine the room from this experiment.
Evaluation
Why did we not calculate the speed of sound from one data point
Why did we not calculate the speed of sound from one frequency?
How could we adapt this experiment to investigate additional factors?
What was the largest source of uncertainty in this experiment and how could it be reduced?
