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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 ╝ 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 ╝ 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 = fĚl

            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 0oC.  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 (21oC).

 

2.                  How does your value compare to the actual speed of sound?

 

(Your value) / (Speed of sound) x 100

 ____________ / _____________ x 100 = _______________

Post-lab Questions:

  1. What type of wave was the wave that you measured in the lab?
  2. Which tuning fork had the longest wavelength and which had the shortest?
  3. What was the medium for the transmission of sound?
  4. Why was the tone the loudest at only certain heights of the resonance tube?
  5. Was there a change in the speed of the wave as you changed tuning forks?  Explain.
  6. What would happen to the distances of the waves if the room was significantly colder that it was today?
 

 

Last modified: September 05, 2004