PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the wavelength of a sound wave from node length data.

INTRODUCTION:
Sound waves are longitudinal waves which require a medium, such as air or water, in which to travel. Sound does not travel in a vacuum. In our experiment we will confine the sound waves to move in one direction with the use of a resonance tube apparatus. Within the tube is a movable piston which effectively closes off one end of the tube. When a sound wave is produced by a tuning fork located at one end of the tube, it will propagate along the tube's volume until it hits the piston, where it is reflected back towards the open-end of the tube. The piston can effectively alter the length of the tube, causing the incident and reflected waves within the tube to interfere in such a way as to maximize the amplitude of the sound waves. When this occurs, the standing waves created within the tube are said to be in resonance. When resonance is reached, the volume of the exiting sound is greatly increased. Resonance is reached when the piston within the tube reaches a "node" in the sound wave. The diagram below shows 4 nodes forming within a tube. During this lab you will adjust a wooden piston until a node in a resonance wave is found.

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A tuning fork will supply the sound waves used in this lab. When gently struck against a standing object the fork will vibrate at a set frequency for a short time. Several strikes will be required during the lab.

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A hand held sound meter will be used to determine when the loudest sound is produced and thus a node is reached.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

2) Record the diameter of your sound tube and the speed of sound within your lab, both of which are displayed. Room temperature and humidity can change the speed of sound.

3) Drag the volume meter, mounted on the ring stand by a clamp, so that its top sensor is just below the lip of the sound tube. Click on the red button on its face to turn the unit on. Too high or too low a position will not allow the meter to get an accurate reading.

4) Pick up the tuning fork and strike it against the shelf on the right side of the screen. This will set it into motion and produce a sound wave for the lab. Position the fork to the left of the sound tube so it is about 8 cm over and center the tines on the sound tube. Note: the tuning fork will vibrate for just so long so you will have to strike it on the shelf to continue through the lab. A side note: the handle of tuning forks is located at a node in the vibrational pattern of the fork and thus does not interfere with its vibrating.

5) Drag the piston within the sound tube to the right and observe the value on the sound meter. Stop when the highest value is reached, this is the location of node 1. Pick up the ruler and measure the distance from the open end of the sound tube to the face of the piston and record as node 1(in meters). Continue down the tube with the piston and you will find node 2. Record this distance. Note: the sound meter has been set to multiply the bB value of the sound it detects. A reading in the 80 dB range would actually be equal to a lawn mower! The data sheet for this lab indicates that you have to calculate the 3rd node for this tube. As it turns out, that would be beyond the actual length of the tube, BUT it can still be calculated.

6) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.