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# Re: Standing waves.

what makes you think the signal amplitude is constant? YOu're using a
"strobe" on the piston? Is its amplitude constant? Check the resonance
by "uncoupling" the speaker from the amplifier with an ~ 100 Ohm
resistor and measuring the EMF at the speaker. My memory, if served,
is, the resonance is near the bottom of the range you are using. [I
think I have the same vibrator and Pasco's osc./ amp.] the string does
not load the speaker, so the resonance isn't damped (much).

bc

Ludwik Kowalski wrote:

How to explain this in an introductory physics course?

Standing waves apparatus from Pasco is
used to observe loops established on a
string at frequencies corresponding to the
known L, tension, and mu. In preparing for
tomorrow's lab I saw that the amplitudes of
4 cm when the lambda is 2*L to about 0.2
cm when lambda is 9 times shorter.)
Why is it so?

My setup: Pasco vibrator SF-9324
Soft threaded string mu=0.00160 kg/m and
L=126.5 cm,
Pasco generator (amplitude was constant (in
the middle of the range) only frequencies were
changed from about 14 Hz to 128 to observe
1, 2, 3, 4, ...9 loops.

Why do the amplitudes of standing waves
decrease while the signal amplitude of the
source remains the same?
Ludwik Kowalski