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Name
Date
Physics 100
Winter 2008
Standing Waves on a String
For this Lab, you will use a mechanical vibrator with adjustable frequency to study
standing waves on a string with 2 different tensions. Using the equation
v = f
Eqn (1)
where:
v = wave speed in m/s,
 = wavelength in m,
f = frequency in Hz or s-1,
you will measure wavelength, set frequency to obtain the appropriate standing wave and
calculate wave speed.
Procedure
1. Refer to Figure 1. Put 50 g on the weight hanger and hang this weight on the
string going over the pulley. This will set your first, lower, string tension. Note
that the weight hanger is 50 g and that the total weight tensioning the string is due
to the weight of 100 g of mass.
2. Before adjusting vibrator frequency, ‘twang’ the string in the middle. This will
give you a crude estimate of the frequency of the 1st harmonic, f1, also called the
fundamental.
3. Use your estimate for f1 to set vibrator frequency.
4. Fine tune vibrator frequency to obtain the lowest order standing wave. The string
will have a large amplitude and will have exactly 2 nodes and 1 antinode. It
should look like the top picture in Figure 2.
5. For the first harmonic, the wavelength is half the string length from the vibrator to
the inner pulley edge.(See Figure 2.)
6. Record the frequency and the wavelength in Table 1.
7. Calculate wave speed, v, using Eqn (1) and enter into Table 1.
8. Increase vibrator frequency to f2 = 2 f1. There will again be a large amplitude at
the antinodes and there are 2 antinodes and 3 nodes. See Figure 2, middle part.
9. Observe the second order standing wave.
10. Enter f2 and the wavelength into Table 1. Note that wavelength for the 2nd
harmonic is half the string length from vibrator to pulley edge.
11. Calculate wavespeed using your data from the 2nd harmonic in Eqn (1) and enter
into Table 1.
12. What do you expect the frequency, wavelength and wave speed to be for the 3rd,
4th and 5th harmonic? Enter the appropriate values in Table 1.
13. Repeat the procedure with a 100 g mass on the 50 g weight hanger. Enter the
data into Table 2.
Figure 2