Speed of Sound practical using a standing wave in a pipe.
Aim and background.
The aim of this practical is to enable to you to find the speed of sound in air by using a length of plastic tubing and a
tuning fork. In order to be successful in the practical you need to pay attention to your teacher’s demonstration.
Tuning forks are made in such a way that when they are struck they emit a musical note at a precise frequency
(hertz) which does not change. Tuning forks can be made to sound at all notes (sharp and flat). The note and/or
frequency that your tuning fork emits will be stamped on the side of it. Whatever the frequency of the note of the
tuning fork, the speed at which the sounds travels will be more or less constant allowing for changes in temperature
of the air.
Equipment list
Tuning fork
Plastic tubing with centimetre markings
Large measuring cylinder
Block of wood
Method
Having watched the demo and listened to guidance this will be quite straight forward. You need to be precise in
your measurements.
1.
Set up your measuring cylinder you have been shown. Remember you don’t need to fill your cylinder right to
the top. You must measure the inside diameter of the plastic tube in metres and record it in your table of
results.
2.
Hold the plastic tube in the water so that one end is closed. Don’t drop it.
3.
Strike the tuning fork on the wooden block and hold it over the open end of the plastic tube.
4.
Now move the fork and tube up or down until the note you can hear sounds loudest.
5.
Record this length of plastic tubing in your table of results and repeat two more times and calculate the
average length of plastic tube in metres.
Calculating the Speed of Sound
Once you have calculated the average length of plastic tubing there is a correction factor that needs to be applied.
You should now add to the average length of the tube the correction factor which is 0.4 x inside diameter of the
plastic tubing. Record this corrected value in the correct column of your table of results.
The value that you have recorded is in fact one-quarter of the wavelength of the note of your tuning fork. You
should now multiply your corrected value by 4 to give you the wavelength in metres. Record this value in your table
of results.
Now that you know the frequency (Hz) of your tuning fork and the wavelength (λ) of the note you can calculate the
speed of sound using the equation
𝑽=𝒇𝒙𝝀
Column headings for table of Results
1
2
Frequency Inside
of tuning
diameter
fork (Hz)
of plastic
tube (m)
3
Length of plastic
tubing (m)
1
2
3
4
5
6
Average
length of
tubing
(m)
Correction
factor (0.4
x inside
diameter of
plastic
tubing)
Correction
factor +
average
length of
tubing
(5 + 4)
7
8
Actual
Speed of
wavelength Sound
using
(column 6 x 𝑽 = 𝒇 𝒙 𝝀
the
number 4)
I have calculated the speed of
sound to be:
m/s