PASCO WA-9867 Sine Wave Generator User Manual

Page 17

Model No. WA-9867

Experiment 1: Standing Waves In Strings

Setup

1. As shown in the picture, clamp the Sine Wave Generator and pulley about 120 cm apart.

Attach about 1.5 m of braided string to the vibrating blade, run it over the pulley, and hang
about 150 g of mass from it.

2. Measure from the knot where the string attaches to the string vibrator to the top of the pulley.

This is distance L. (Note that L is not the total length of the string, only the part that is
vibrating.)

3. Turn on the Sine Wave Generator and turn the Amplitude knob all the way down (counter-

clockwise). Connect the Sine Wave Generator to the string vibrator using two banana patch
cords. Polarity does not matter.

Part I:

Wavelength and Frequency

Procedure

1. Set the Amplitude knob about midway. Use the Coarse (1.0) and Fine (0.1) Frequency knobs

of the Sine Wave Generator to adjust the vibrations so that the string vibrates in one segment.
Adjust the driving amplitude and frequency to obtain a large-amplitude wave, but also check
the end of the vibrating blade; the point where the string attaches should be a node. It is more
important to have a good node at the blade than it is to have the largest amplitude possible.
However, it is desirable to have a large amplitude while keeping a good node.

2. Record the frequency. How much uncertainty is there in this value? How much can you

change the frequency before you see an effect?

3. Repeat steps 1 and 2 for a standing wave with two segments. The string should vibrate with a

node at each end and one node in the center.

4. How is the frequency of the two-segment wave related to the frequency of the one-segment

wave? Calculate the ratio of the frequencies. Is the ratio what you would expect?

5. With the wave vibrating in two segments, the length of the string, L, is one wavelength

(L =

λ). Does it look like one wavelength? Since the string vibrates up and down so fast, it is

hard to see that when one side is up, the other is down. Examine the vibration of the string