PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the frequency of a standing wave by the tension level placed on a vibrating string.

INTRODUCTION:
If a string is strung between two points and vibrated, a standing wave can be generated by adjusting the tension on the string. The point at which the string is attached to the vibrator(on the left) and the point at which the string hangs over the pulley(on the right) are considered nodes. As the tension is changed, a standing wave(harmonic) with the two end nodes and a single central antinode can be formed. This is the 1st harmonic wave or fundamental wave with the designation n=1. The second. third and forth harmonic waves can be generated during this lab, 5th, 6th, etc. are possible with other lab setups. A standing wave is generated when the incident and reflective waves match and the wave appears to stop moving or "standing".

The wavelength of our standing wave can be calculated using the equation:

wavelength = 2L/n

where L is the length of our string and n represents the harmonic (1 antinode, 2 antinodes, etc.). The frequency of our standing wave is calculated by using the equation:

f = sqrt(T/(mul x wavelength²))

where mul = mass per unit length of the string and T = tension on the string. During this lab you will calculate the frequency at each harmonic wave and determine the average for your set up.

---*---

A wave generator will vibrate a string at a set frequency hooked to the above set up.

---*---

The tension on the string will be generated by the above apparatus. A 1 kg weight can be adjusted on a meter stick to provide the different masses needed to produce the first 4 standing waves (harmonics).

---*---

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.

---*---

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 mass per unit length for your string (listed on the screen). Pick up the meter stick on the table and measure the length of the string from the wave generator to the center of the pulley on the right. Record in meters.

3) Turn on the wave generator by clicking on the red button on the front of the unit. If not enough mass is pulling on the string over the pulley, the string tends to have a random like movement. Move the hanging kg weight to the right on the meter stick. Since the meter stick is hinged to the stand on the left, only a portion of its mass is actually pulling down on the string. As you move to the right, observe the different standing waves formed from n=4 down to n=1. Reset the hanging kg mass to the far left.

4) Slowly drag the hanging mass to the right and try to find the exact point at which the n=4 standing wave is formed. At this point the wave will have the largest amplitude. The point for this standing wave will be close to the left end of the meter stick. Record the distance from the left end of the meter stick to where the hanger is now pointing to (in meters).

5) Continue to drag the mass to the right and find the first point at which the wave n=3, n=2 and n=1 is formed. Record their distances in meters. The fundamental or n=1 wave will be the furthest to the right.

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.