PASCO WA-9867, Инструкция по эксплуатации

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Sine Wave Generator Standing Waves In Strings
16
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A stretched string has many natural modes of vibration (three examples are shown above). If the
string is fixed at both ends then there must be a node at each end. It may vibrate as a single
segment, in which case the length (
L ) of the string is equal to 1/2 the wavelength (
λ
) of the wave.
It may also vibrate in two segments with a node at each end and one node in the middle; then the
wavelength is equal to the length of the string. It may also vibrate with a larger integer number of
segments. In every case, the length of the string equals some integer number of half wavelengths.
If you drive a stretched string at an arbitrary frequency, you will probably not see any particular
mode; many modes will be mixed together. But, if the driving frequency, the tension and the
length are adjusted correctly, one vibrational mode will occur at a much greater amplitude than
the other modes.
For any wave with wavelength
λ
and frequency f , the speed, v, is
(eq. 1) v =
λ
f
In this experiment, standing waves are set up in a stretched string by the vibrations of an
electrically-driven string vibrator. The arrangement of the apparatus is shown below. The tension
in the string equals the weight of the mass suspended over the pulley. You can alter the tension by
changing the mass. You can adjust the amplitude and frequency of the wave by adjusting the
output of the Sine Wave Generator, which powers the string vibrator.
L
String
String
Vibrator
Hanging
Mass
Pulley