Wave Characteristics Experiment

Starter

A wave is 2m long and passes by in 4 seconds.What is the wave speed?

v = d/t = 2m/4s = .500 m/s

Traveling Wave Formulas

Period : T = time taken for 1 wavelength to pass by

Frequency : f = how many waves pass by in 1 second

f = 1/T v = lf = l/T

ExampleA water wave has a wavelength of 2 meters andpasses by a stationary observer in 3 seconds.

1.What is the frequency of the wave?

f = 1/T = 1/3 = .33Hz

2.What is the wave speed?

v = lf = (2)(.33) = .66 m/s

Part I: Finding the Wave Speed and Frequency

Open the phet “Waves on a String” simulation. Note that you can create a wave three different ways: manual, oscillate, or pulse. The string can be attached at the right end three different ways: fixed, loose, or no end.

At the top you can set the Amplitude, Damping, Frequency, and Tension.  Important: The “Frequency” setting ( 0 – 100) does not correspond to Hertz; it is just a relative setting. You will calculate the correct frequency yourself.  You may use the ruler and timer ( which are accurate in meters and seconds ) to measure the wavelength and period of the wave.  Set the string with the following settings: Amplitude = 50, Damping = 0, Tension = 10 ( highest setting), Oscillate, and No End.

K:\Davenport Pre AP Physics\wave-on-a-string_en.jar

"f" Tension Measure Measure Calculate Calculate

    l (m) T(s) f (Hz) v (m/s)

25 10        

50 10        

75 10        

25 7        

50 7        

10 7        

A. Set the frequency to 25 and produce a wave. Use the tools to measure the wave length and the period. Note that you can step the wave with the timer on to slow down the motion and measure the period. B. Calculate the frequency in Hertz and the wave speed in meters/second. C. Repeat these steps for a “frequency” setting of 50, and 75. Record

your measurements and calculations in an excel spreadsheet. D. Set the tension to 7, and repeat for frequencies of 10, 25 and 50.

Part II: How Waves Reflect

A. Set the tension to 10, the amplitude to 50, and the damping to zero. B. Set the source to PULSE. Observe the reflected pulse for a fixed end, and a loose end. Draw the initial pulse, and the reflected pulse for each end type.

Questions1. What did you notice about the wave speed for different frequencies, but the same tension? 2. When the tension was lowered, what happened to the wave speed? 3. State a rule for what a reflected pulse looks like for a fixed end, and a loose end. 4. Two strings on a guitar have the same length, but different frequencies. How could you tell which string was under the greater tension just by listening to the plucked strings? Explain carefully.  5. A person watching water waves notes that 3 complete wave pass by in 4 seconds. She also notices that each wave is 1.5m long. Calculate the wave speed, the period, and the frequency.  6. Middle C on a piano is 261.6 Hz. The speed of sound is 344 m/s. Find the wavelength and period of this sound wave. 

Report Checklist

A.Data table from Part I.

B.Two drawings from Part II.

C.Write out the 6 questions and answer them in complete sentences.

Each student must hand in: