Resonance in a Closed Air Column - Lab Instructions - classconnect

Resonance in a Closed Air Column
An air column that is closed at one end and open at the other is called a closed air column.
When a vibrating tuning fork is held over the open end of such a column and the length of
the column is increased, the loudness increases sharply at very specific lengths (see Figure
1). If a different tuning fork is used, the same phenomenon is observed except the sound
maximum occurs at different lengths. In this investigation, you will use the relationship
between the frequency of the tuning fork and the resonant length of a closed air column to
determine the speed of sound in the column.
Questions
How does the speed of sound change for different frequencies?
How does the speed of sound change for different temperatures?
Figure 1
Process
1. Predict how you think the speed of sound for one tuning fork frequency will compare with another.
Predict how the temperature of the air will affect the speed of sound. Explain your predictions.
2. When sound waves travel down a long tube, they reflect off of the closed
end. Certain tube lengths will allow the sound wave to end perfectly on a
node (see Figure 2). At this length the incoming waves and the reflecting
waves will interfere to form a standing wave and mechanical resonance
will be observed by a distinct increase in the sound intensity.
Figure 2
3. Measure the length of the tube where the first resonance is observed. Repeat this step multiple times
to make sure that your measurements are accurate and take an average of the data.
4. Use your measured length to determine the wavelength of the sound wave.
5. Create data tables to keep track of your observations.
Trial
1
2
3
AVG
Trial
1
2
3
AVG
Tuning Fork 1
Room Temperature
1 st Resonant
Length
of Tube (m)
Average
Wavelength
Tuning Fork 1
Different Temperature
1 st Resonant
Average
Length
Wavelength
of Tube (m)
Tuning Fork 2
Room Temperature
1 st Resonant
Length
of Tube (m)
Average
Wavelength
Tuning Fork 2
Different Temperature
1 st Resonant
Average
Length
Wavelength
of Tube (m)

Answer the following questions. Always use full sentences. When necessary, be sure to show your
calculations in a neat and organized way.
Knowledge and Understanding
1) What is the wavelength of sound emitted by each tuning fork in this investigation? (4 marks)
2) Use the wavelength from each tuning fork to calculate the speed of the waves using the universal
wave equation. (4 marks)
3) How does the wave speed of the first tuning fork compare to the wave speed of the second tuning
fork when they are at the same temperature – are they the same speed, or is one faster/slower? Are
you surprised? (2 marks)
4) How does the wave speed of the tuning forks at room temperature compare to the wave speed of
the tuning forks at a different temperature – are they the same speed, or is one faster/slower? Are
you surprised? (2 marks)
5) Calculate what the speed of sound should be based on the temperature of the air in each location.
(2 marks)
Thinking and Investigation
6) Calculate the % error of your experimental results using the formula on page 565 of your
textbook. (Note: This is a comparison of the “experimental” speed obtained in question 2, to the
“accepted” speed from question 5) Does your % error seem reasonable for this type of lab?
Explain. (4 marks)
7) Describe at least two sources of reading error and systematic error in your investigation. Explain
how each error may have affected the final results. Estimate a +/– value for the reading error of
your measurements and explain how you determined it. (5 marks)
8) Reflect on the process of collecting data. Identify at least one thing you would do differently to
improve the lab if you were to do it again. (2 marks)
9) Write a conclusion that answers the questions at the beginning of the lab. Address whether or not
you believe the conclusions formed from this lab are correct and why. (3 marks)
Application
10) In this investigation you observed resonance in a closed air column. You can also observe
resonance by pushing a child on a swing. Compare the child on the swing to the column of air.
Explain how they are both demonstrations of the same phenomenon? (5 marks)
11) Wind instruments typically consist of a mouthpiece or reed attached to a long tube filled with air.
The metal tube merely serves as a container for a column of air. Explain how these instruments
are a specific application of resonance in a closed air column. Be specific: What causes the
vibration? What changes the length of the tube? (5 marks)