When a wave fits perfectly within boundary conditions, it will resonate. That is, a series of waves will reflect and interfere with each other to make a standing wave. When this happens with a sound wave, the result at the open end of the tube is much louder than the sound that makes the original wave. At the open end of the tube there will be constructive interference. img/img_standingwaves_25.gif

In this diagram you see what standing waves on a string look like when the two ends are fixed, like on a guitar or a violin. Standing waves only occur when the wavelength is just right and there are nodes at the locations where the string is unable to move. The top picture represents ½ of a wave fitting within the boundaries. The second picture represents exactly 1 wave fitting within the boundaries. The third and fourth pictures represent 3/2 of a wave and 2 waves fitting within the boundaries.

img/img_restube_24.gif

This lab sets up a closed system where the node is located at the top of the water column and the antinode is located at the top of the air column. When different tuning forks are placed above the air column, different sounds are produced. By adjusting the air column, the antinode can be located at the location where there is a deep, reverberating sound. The loudest sound will occur when the length of the air column is equal to ¼ of the wavelength.

Assignment Directions

Safety

There are no safety considerations as the data shall be taken from an actual experiment performed on video.

Materials

The experiment will take place using 8 tuning forks, a rubber mallet, a glass tube, a large graduated cylinder or other container filled with water, and a meter stick.

Procedure

Steps 1-3 will be completed on the video. You will determine the length of the tube in step four by watching the video and reading the meter stick.

The glass tube shall be held upright in water with most of the tube submerged.

A tuning fork with a frequency of 512 Hz will be struck with a mallet so it vibrates properly.

While holding the tuning fork vertically just over the open end of the glass tube, the tube should be raised until the resonating sound of the tuning fork can be heard throughout the room.

While the resonating sound is present, the length of the glass tube from the water level to the top should be measured with a meter stick to the nearest millimeter.

The data should be recorded on the data table. The frequency comes from the tuning fork. The wavelength is 4 times the length of the tube above the water. Make sure you record the wavelength in meters. (See the introduction if you are not sure why you are multiplying the length of the tube by 4.)

Repeat the experiment with 7 more tuning forks at their given frequencies.

SHOW TRANSCRIPT:
Sound Resonance

For this resonance experiment, the temperature in the room is 29 degrees Celsius. [Mercure of the thermometer stopping at 29 degrees Celsius] This is a 256 hertz tuning fork resonating in a glass tube. [The experimenter strikes the tuning fork against the palm of his hand and then hold it in the glass tube. Another experimenter holds up a meter stick vertically on the table next to the glass tube. A resonating sound can be heard more and more distinctly as the tube is raised. While the resonating sound is in full force, the length of the glass tube is measured with a meter stick.

This process is repeated for a 288 hertz, a 320 hertz, a 341.3 hertz, a 384 hertz, a 426.6 hertz, a 480 hertz, and a 512-hertz tuning forks resonating in the glass tube. For each tuning fork resonating in the glass tube, a measure to the nearest millimetre is taken while the tube is raised until the tuning fork’s full resonance.]

Questions

Complete the data table using the procedure above and the video provided. To find the distance from the top of the water column to the top of the air column, subtract the height of the water column from the total distance to the top of the air column.

Using the equation v = fƛ, determine the wave speed for each trial.

Determine an average wave speed by averaging the wave speeds you found for each trial.

To calculate the exact value for the speed of sound, use the temperature given at the beginning of the video and the following equation: Vsound = 331 m/s + 0.6(TCelcius)

How close was your average speed to the calculation of the actual value for the speed of sound in m/s? Give 2 examples of errors that may have occurred during the lab that could have caused your value to be different than the value that you determined using the equation.

QUESTIONS:

To fully complete this project, you will submit the following:

Complete the data table with values that you determine from the video and calculated.

Find the average wave speed as asked for in question 3.

Find the mathematical speed of sound as asked for in question 4. Show your calculation.

Answer to question 5 in complete sentences.

datasheet included