
CP Sci 9 1st Sem. Gen Chem  1st Sem. 
Objective: 1.
The
student will use the concept of resonance to calculate the wavelength of sound
at a known frequency. 2.
The
student will be able to calculate the speed of sound using the concept of
resonance. Equipment: 1.
Resonance
tube approximately 50cm long 2.
1L
plastic graduated cylinder 3.
Meterstick 4.
3 tuning
forks > 256Hz Discussion:
There are many examples of resonance around us every day.
You may have heard something vibrating in your car while a particular
song plays on the radio. The
frequency of the note in the song was equal to the natural frequency of whatever
was vibrating.
Gasses can vibrate as well; organ pipes and soda bottles make sound by
resonating air. A vibrating tuning fork held over an open tube may vibrate
the air column in it at its resonant frequency.
The length of the air becomes loudest at the proper length for maximum
resonance at the frequency of the tuning fork.
For a tube open at one end and closed at the other, resonance first
occurs at ¼ the wavelength of the sound wave.
(think of sonar) Procedure: 1.
Fill the
graduated cylinder about 2/3 full and place the resonance tube in the cylinder. A.
The length of the resonance tube will be varied by moving it up and down. 2.
Select a
tuning fork and record its frequency. Frequency = ________________Hz 3.
Find the
first harmonic. A.
Strike
the tuning fork on the heel of your shoe (Not on the cylinder).
B.
Hold the
tuning fork with its tines one above the other, 1cm above the open end of the
resonance tube. C.
Move the
fork and the tube up and down, together, to find the point where the air column
gives the loudest sound. D.
Hold the
resonance tube steady and have your lab partner measure the distance from the
top of the tube to the water level and record. Length of air column = _________________m 4.
Measure
the diameter of the resonance tube. Diameter of the resonance tube = _______________m 5.
Make a
corrected length by adding 0.4 times the diameter of the tube to the measured
length of the air column. This
corrected length accounts for the small amount of air just above the tube that
also vibrates. Corrected length = ______________m 6.
The
corrected length is ¼ of the wavelength of the sound vibrating in the air
column. Compute the wavelength of
that sound. Wavelength = _______________m 7. Using the frequency
and the wavelength, Calculate the speed of sound in air using the formula:
speed = f·l
Speed of sound in air = ___________________m/s Repeat
the above steps using a tuning fork of a different frequency.
Frequency =
_____________________Hz
Length of air column =
_____________________m Corrected length =
_____________________m Wavelength =
_____________________m Speed of sound in air = _____________________m Checking
you accuracy: 1.
The
accepted value for the speed of sound in air is 332m/s at 0^{o}C.
The speed of sound in air increases by 0.6m/s for each degree Celsius
above zero. Compute the speed of
sound at room temperature (21^{o}C). 2.
How does
your value compare to the actual speed of sound? (Your value) / (Speed of sound) x 100 ____________ / _____________ x 100 =
_______________ Postlab Questions:

Last modified: September 05, 2004 