Speed of Sound Lab
Introduction
In this lab you will determine the speed of sound by finding the harmonics of a closed ended tube.
Diagram
Theory
Resonance occurs when the standing or stationary waves produced have maximum amplitude. A
node of high pressure and density is formed at the water boundary and an anti-node of low
pressure and density is formed a short distance, e, above the open end of the tube. The
temperature of the air column will affect the speed of sound. The average speed of the air
particles is greater at higher temperatures and therefore they can pass on compressions and
rarefactions more quickly.
The longest wavelength producing resonance is about equal to four times the length of the air
column, L plus the end correction e.
 = 4(L+ e)
or
/4 = L + e
The speed of sound at a particular temperature is given by v = f 
Therefore:
/4 = L + e = v / 4 f
or
L = ( v / 4f ) – e
Plotting a graph of L against 1/f for different tuning forks produces a linear graph with a slope of
v/4 and a y-intercept of –e.
A published relationship between speed and temperature shows that
where v = 331 ms-1 at 273 K.
Things to do
A vibrating tuning fork will be held near to and over the open end of a tube whose other end will
be in water. Moving the tube up or down will allow you to change the length of the tube while
keeping one end closed. At some definite length (L), the sound of the tuning fork will be
significantly louder due to the presence of the standing wave in the air column. Find the smallest
length of tube above the water that will give the loudest sound. You will need to make small
adjustments to locate the loudest sound.
For each of five tuning forks, make sufficient measures of the length(s) needed to achieve
resonance so that you are confident of the results.
Measure the room temperature
Data Processing and Presentation
Using the equation : L + e = v / 4 f
plot a graph that allows you to determine the speed of
sound. From the graph determine the speed of sound, v.
Calculate the speed of sound, v, in the lab using the published relationship (shown above)
Discussion
Compare your value of v with the one calculated using the published relationship at that
temperature. Comment on sources of error.