PRACTICE IT Use the worked example above to help you solve this problem. A pipe is 2.42 m long. (a) Determine the frequencies of the first three harmonics if the pipe is open at both ends. Take 345 m/s as the speed of sound in air. f₁ = Hz f₂ = Hz √3 Hz (b) How many harmonic frequencies of this pipe lie in the audible range, from 20 Hz to 20000 Hz? (c) What are the three lowest possible frequencies if the pipe is closed at on end and open at the other? f₁= √3= fs= Hz Hz Hz
PRACTICE IT Use the worked example above to help you solve this problem. A pipe is 2.42 m long. (a) Determine the frequencies of the first three harmonics if the pipe is open at both ends. Take 345 m/s as the speed of sound in air. f₁ = Hz f₂ = Hz √3 Hz (b) How many harmonic frequencies of this pipe lie in the audible range, from 20 Hz to 20000 Hz? (c) What are the three lowest possible frequencies if the pipe is closed at on end and open at the other? f₁= √3= fs= Hz Hz Hz
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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Question

Transcribed Image Text:PRACTICE IT
Use the worked example above to help you solve this problem. A pipe is 2.42 m long.
(a) Determine the frequencies of the first three harmonics if the pipe is open at both ends. Take
345 m/s as the speed of sound in air.
f₁ =
Hz
f₂ =
Hz
f3
Hz
=
(b) How many harmonic frequencies of this pipe lie in the audible range, from 20 Hz to 20000 Hz?
(c) What are the three lowest possible frequencies if the pipe is closed at on end and open at the
other?
f₁ =
f3=
=
f5
=
Hz
Hz
Hz

Transcribed Image Text:GOAL Find frequencies of open and closed pipes.
PROBLEM A pipe is 2.46 m long. (a) Determine the frequencies of the first three harmonics if the
pipe is open at both ends. Take 343 m/s as the speed of sound in air. (b) How many harmonic
frequencies of this pipe lie in the audible range, from 20 Hz to 20000 Hz? (c) What are the three lowest
possible frequencies if the pipe is closed at one end and open at the other?
STRATEGY Substitute into the all harmonics (open ended) equation for part (a) and the odd numbered
harmonics (one end closed) equation for part (c). All harmonics, n = 1, 2, 3 . . . are available for the pipe
open at both ends, but only the harmonics with n = 1, 3, 5, . . . for the pipe closed at one end. For part
(b), set the frequency in the odd numbered harmonics equation equal to 2.00 x 104 Hz.
SOLUTION
(A) Find the frequencies if the pipe is open at both ends.
Substitute into whole harmonics
equation, with n = 1.
Multiply to find the second and third
harmonics.
This works out to n = 286.88, which
must be truncated down (n = 287
gives a frequency over 2.00 x 104 Hz).
f₁
The next two harmonics are odd
multiples of the first:
=
f₂ = 2f1
fn
V
2L
(B) How many harmonics lie between 20 Hz and 20000 Hz for this pipe?
Set the frequency in the harmonics
equation equal to 2.00 x 104 Hz and
solve for n.
f₁
V
2L
n = 286
(C) Find the frequencies for the pipe closed at one end.
Apply the one end open harmonics
equation with n = 1.
-
= n
V
4L
343 m/s
2(2.46 m)
f3 = 3f1
=
139 Hz
= 69.7 Hz
343 m/s
4(2.46 m)
f3 = 3f₁ = 209 Hz
343 m/s
2. (2.46 m)
= 105 Hz
= 2.00 × 104 Hz
= 34.9 Hz
f5 = 5f₁=
= 175 Hz
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