AP Physics Laboratory
Resonance Tubes
DISCUSSION:
When pressure waves travel down a close-ended tube they bounce off the close end and reflect. When the
wave interacts with another pressure wave traveling down the tube, interference occurs. When
constructive interference occurs at the antinodes it creates resonance, an increase in the amplitude of the
waves.
At the fundamental harmonic, the first harmonic, of a close-ended tube, a node occurs at the closed end
and an antinode occurs at the open end. Thus, the length of the tube is equal to one-fourth of the
wavelength. Because it is necessary to have an antinode at the open end, each harmonic frequency will
occur in one-half wavelength increments.

l  n 
4
[tube length at each harmonic]
THE EXPERIMENT:
1. Fill the graduated cylinder to within a few inches of the top with water. Place the glass tube into the
graduated cylinder to be sure the water level does not exceed the top of the cylinder.
2. Choose a tuning fork and record its frequency.
3. Strike the tuning fork and position the fork about 1cm above the glass tube.
Do not strike the tuning fork on the table, glass tube, or graduated cylinder.
4. Move both the glass tube and the tuning fork in and out of the water until you find the position where
the sound of the tuning fork is maximized. This may require you to strike your tuning fork several
times.
5. When you locate the maximum sound, measure the distance from the top of the glass tube to the
water level.
6. Make a corrected length by adding 0.4 times the diameter of the tube to the measured length of the
air column. This length accounts for the small amount of air just above the tube that also vibrates.
The corrected length is one-fourth of the wavelength of the sound vibrating in the air column. Record
the wavelength.
7. Determine the velocity of sound and record.
8. Repeat each of the above steps for a second tuning fork.
9. The accepted value for the speed of sound in air is 332m/s at 0C. The speed of sound in air increases
by 0.6m/s for each degree C above zero. Determine the temperature of the room and calculate the
speed of sound in the room.
ANALYSIS:
In addition to any necessary measurements or calculations from the experiment itself, include the
following in your lab report.
10. Determine the percentage difference between the velocity of sound as calculated using harmonics
and the actual value using room temperature.