PHY124
Lab # 2
Speed of Sound
Name____________________
Lab Partners:
Purpose: The purpose of this lab is to measure the speed of sound in air by using six
tuning forks and a resonant air column.
Apparatus
6 Tuning forks with different frequencies
1 section of PVC pipe
1 Large cylinder
1 Metrestick
1 Thermometer (Celsius)
Procedure
1) Place the PVC pipe inside the glass cylinder.
2) Fill the glass cylinder with water. (Up to within 2 or 3 cm of the top of the tube.)
3) Strike the first tuning fork with the rubber mallet (or on your knee) and hold it over
the top of the PVC pipe that is inside the glass cylinder. (Keep the tuning fork at least
3 cm above the top of the PVC pipe.)
4) Slowly lift the PVC pipe out of the glass cylinder and out of the water until you find
the distance that gives you the loudest volume (find the length that causes resonance).
5) Measure and record the distance from the top of the PVC pipe to the water level.
6) Measure and record the air temperature.
7) Record the frequency of the first tuning fork.
8) Repeat the previous steps for the other five tuning forks.
9) Measure and record the inside diameter of the PVC pipe.
10) Calculate the Percent Relative Error by comparing the calculated speed of sound
based upon the frequency and wavelength (this is the “measured” speed of sound) and
the “accepted” speed of sound (which is based on the air temperature).
Data table for lab # 2
Speed of Sound Lab
Inside diameter of PVC pipe.
Frequency
of Tuning
Fork
Length of Tube
Above Water
__________
Calculated
Wavelength
Calculated
“measured”
Speed of Sound
Air
Temperature
Calculated
“accepted”
Speed of Sound
Percent
Relative
Error
(Optional)
Frequency of Unmarked
Tuning Fork
Length of Tube Above
Water
Calculated Wavelength
Air
Temperature
Speed of Sound
Questions for lab # 2
Speed of Sound Lab
1) How might you change the lab to increase the accuracy of the calculated speed of
sound?
2) Explain how you would use what you have done in this lab to find the frequency of an
unmarked tuning fork. (Give the equations in the form you would use as well as how you
got them.)
3) Why is the “end-correction factor” more critical for higher frequencies than it is for
low frequencies?
4) In this lab all of your measurements were taken at the shortest length of the PVC pipe
above the water that caused the air inside the pipe to resonate. Using the frequency of the
first tuning fork from your lab, what would be the minimum length of the PVC pipe
required to find the next shortest length of PVC pipe above the water level that will cause
the air inside the pipe to resonate?