E-407
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EXPERIMENTS Standing waves in an air column
Purpose Theory
This experiment investigates the positions of nodes and Please refer to the preceding page.
anti-nodes in a standing wave.
Procedure Is there a node or an anti-node at the end of the tube?
Was this as you expected ?
A – Closed pipe
The velocity of sound can be found when wavelength
and frequency are known:
Compare this to the table value for dry air at tempera ture
If the piston is in position in the tube, remove it. Put on
T
c
(centigrade):
both of the end caps. Connect the microphone and the
loudspeaker as shown.
Insert the microphone probe with only the tip through the
end opposite the loudspeaker.
Adjust the frequency f to approximately 1000 Hz and
B – Half-open pipe
check that the meter is giving a reading. Next the fre -
quency should be adjusted to a resonance (a maximum
reading). This happens for instance at around 953 Hz if
the temperature is 20 °C. Keep the frequency fixed.
Now insert the microphone probe slowly into the reso-
Remove the microphone probe from the end cap and
nance pipe and observe the waning and waxing of the
remove the cap completely. Place the tip of the micro -
amplitude of the sound.
phone into the tube about 8 cm from the end.
Determine the position of a number of nodes (or anti-
Start again at about 1000 Hz and search for a resonan-
nodes) this way. Use the results to calculate the wave-
ce. You may hit one near 993 Hz – depending on the
length λ.
temperature.
Repeat the examination of nodes and anti-nodes as in
part A. Compare with theory.
Can you determine the exact position of the node at the
end of the tube?
®
Science Equipment for Education Physics
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