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An organ pipe has two successive harmonics with frequencies 1372 and 1764 \(\mathrm{Hz}\) (a) Is this an open or a stopped pipe? Explain. (b) What two harmonics are these? (c) What is the length of the pipe?

Short Answer

Expert verified
(a) Stopped pipe. (b) 3rd and 5th harmonics. (c) Length is 0.4375 meters.

Step by step solution

01

Identify the type of harmonics

Identify whether the harmonics given are close in sequence (e.g., successive odd or even harmonics). In a closed pipe (stopped), only odd harmonics exist, resulting in harmonics like 1st, 3rd, 5th, etc. In an open pipe, harmonics follow the 1st, 2nd, 3rd, etc., sequence.
02

Calculate the difference in harmonic numbers

Let's calculate the number of harmonic difference. If \( n \) and \( (n+1) \) are the two successive harmonics, then the frequency difference \( f_2 - f_1 = hf \) where \( h \) is the original frequency. Here, \( f_2 = 1764 \text{ Hz} \) and \( f_1 = 1372 \text{ Hz} \). Thus, the difference \( f_2 - f_1 = 392 \text{ Hz}.\)
03

Determine type of pipe using harmonic difference

In a stopped pipe, the difference in frequency between successive harmonics is larger compared to an open pipe. Here, the difference \( 392 \text{ Hz} \) suggests a substantial spacing consistent with stopped pipes, not open pipes, since adjacent whole number harmonics (e.g., 3rd and 4th in open pipes) would result in smaller differences.
04

Determine the harmonic numbers

For a stopped pipe, the difference in harmonics would usually be between 3rd and 5th harmonics. Let's calculate: if \( f_3 = 3h \) and \( f_5 = 5h \), then \( (f_5 - f_3) = 2h = 392 \text{ Hz} \). Thus, \( h = 196 \text{ Hz} \).
05

Calculate the length of the pipe

The fundamental frequency is given by \( h = \frac{v}{4L} \) for a stopped pipe where \( v = 343 \text{ m/s} \) is the speed of sound in air. Rearranging we find, \( L = \frac{v}{4h} \). Substituting \( h = 196 \text{ Hz} \), we find \( L = \frac{343}{4 \times 196} \approx 0.4375 \text{ meters}.\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Harmonics
Harmonics are essentially the natural frequencies at which an object vibrates when disturbed. These vibrations can create sound waves in musical instruments. For pipes, which are common instruments studied for harmonics, the sequence of vibrational modes is referred to as harmonics. Each harmonic is a multiple of the fundamental frequency.
- For a pipe, this can include the first harmonic (or fundamental frequency) up to higher multiples. - The sequence can vary between open and closed pipes, impacting which harmonic frequencies are sustainable.
Understanding harmonics allows us to determine which sounds are amplified and emitted by the instrument, and thus is vital for musical theory and sound engineering. Imagine pulling strings on a guitar: when you pluck a string, it vibrates and produces different tones that correspond to different harmonics, all related to the fundamental tone. These harmonics create the complex sounds we hear.
Organ Pipe
Organ pipes are fascinating instruments that utilize air columns to produce musical notes. Each pipe is either open at both ends or has one end closed, leading to different sound production characteristics.
- The length and type of pipe (open or closed) determine its fundamental and harmonic frequencies. - In an organ, multiple pipes of varied lengths and structures are used to form a complete range of musical notes.
When air is pushed through the pipe, sound waves are created. These waves meet the boundary conditions (either open or closed), setting up standing wave patterns inside the pipe. The length of the pipe directly influences the fundamental frequency it can produce, as well as the harmonics that can form inside. This makes pipe organs incredibly versatile in musical expression.
Open and Closed Pipes
The distinction between open and closed pipes is crucial in acoustics. This determines the types of harmonics the pipe can produce. - **Open Pipes:** Both ends are open to the air, allowing both even and odd harmonics. The sequence of harmonics for an open pipe is: 1st, 2nd, 3rd, etc. Essentially, all harmonic frequencies can exist here, boosting the variety of notes. - **Closed (Stopped) Pipes:** One end is closed, restricting the harmonics to only odd numbers (e.g., 1st, 3rd, 5th, and so on). This results in fewer harmonic possibilities compared to open pipes.
The boundary conditions at the closed end mean no air movement at that point, creating a node of vibration. This alters the possible harmonics to a subset dominated by odd multiples of the fundamental frequency. Understanding these differences is crucial for accurately deducing the type of pipe based on its harmonic output.
Frequency Calculation
Calculating the frequency of harmonics in organ pipes involves understanding the relationship between the speed of sound, the type of pipe, and its length. The basic formula for calculating frequency in acoustic pipes depends on whether the pipe is open or closed. - In a closed pipe, the fundamental frequency is given by the equation: \[ h = \frac{v}{4L} \] where \(v\) is the speed of sound in air (approximately 343 m/s at room temperature) and \(L\) is the pipe length. - The fundamental frequency \(h\) is multiplied by odd numbers (3, 5, 7, etc.) to find higher harmonics in closed pipes.
Through frequency calculation, you can determine the specific harmonic sequence for a pipe, which is key to understanding and predicting the musical notes that the pipe can produce. By manipulating variables such as pipe length or the speed of sound, one can alter the frequencies generated, enabling vast possibilities in musical compositions.

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Most popular questions from this chapter

Horseshoe bats (genus Rhinolophus) emit sounds from their nostrils and then listen to the frequency of the sound reflected from their prey to determine the prey's speed. (The "horseshoe" that gives the hat its name is a depression around the nostrils that acts like a focusing mirror, so that the hat emits sound in a narrow beam like a flashlight.) A Rhinolophus flying at speed \(v_{\text { tot }}\) emits sound of fre-quency \(f_{\text { but }}\) ; the sound it hears reflected from an insect flying toward it has a higher frequency \(f_{\text { rent }}(\text { a) Show that the speed of the insect is }\) where \(v\) is the speed of sound. (b) If \(f_{\mathrm{bat}}=80.7 \mathrm{kHz}, \quad f_{\mathrm{rell}}=\) \(83.5 \mathrm{kHz},\) and \(v_{\mathrm{bat}}=3.9 \mathrm{m} / \mathrm{s},\) calculate the speed of the insect.

For a person with normal hearing, the faintest sound that can be heard at a frequency of 400 \(\mathrm{Hz}\) has a pressure amplitude of about \(6.0 \times 10^{-5} \mathrm{Pa}\) . Calculate the (a) intensity; (b) sound intensity level; (c) displacement amplitude of this sound wave at \(20^{\circ} \mathrm{C}\) .

Longitudinal Waves in Different Fluids. (a) A longitudinal wave propagating in a water-filled pipe has intensity \(3.00 \times 10^{-6} \mathrm{W} / \mathrm{m}^{2}\) and frequency 3400 \(\mathrm{Hz}\) . Find the amplitude \(A\) and wavelength \(\lambda\) of the wave. Water has density 1000 \(\mathrm{kg} / \mathrm{m}^{3}\) and bulk modulus \(2.18 \times 10^{9} \mathrm{Pa}\) . Water has density 1000 \(\mathrm{kg} / \mathrm{m}^{3}\) at pressure \(1.00 \times 10^{5} \mathrm{Pa}\) and density 1.20 \(\mathrm{kg} / \mathrm{m}^{3}\) , what will be the amplitude \(A\) and wavelength \(\lambda\) of a longitudinal wave with the same intensity and frequency as in part (a)? (c) In which fluid is the amplitude larger, water or air? What is the ratio of the two amplitudes? Why is this ratio so different from 1.00\(?\)

Two identical loudspcakers are located at points \(A\) and \(B\) , 2.00 \(\mathrm{m}\) apart. The loudspeakers are driven by the same amplifier and produce sound waves with a frequency of 784 \(\mathrm{Hz}\) . Take the speed of sound in air to be 344 \(\mathrm{m} / \mathrm{s}\) . A small microphone is moved out from point \(B\) along a line perpendicular to the line connecting \(A\) and \(B(\text { line } B C \text { in Fig. } 16.44)\) (a) At what distances from \(B\) will there be destructive interference? (b) At what distances from \(B\) will there be constructive interference? (c) If the frequency is made low enough, there will be no positions along the line \(B C\) at which destructive interference occurs. How low must the frequency be for this to be the case?

(a) In a liquid with density 1300 \(\mathrm{kg} / \mathrm{m}^{3}\) , longitudinal waves with frequency 400 \(\mathrm{Hz}\) are found to have wavelength 8.00 \(\mathrm{m}\) . Calculate the bulk modulus of the liquid. (b) A metal bar with a length of 1.50 \(\mathrm{m}\) has density 6400 \(\mathrm{kg} / \mathrm{m}^{3}\) . Longitudinal sound waves take \(3.90 \times 10^{-4} \mathrm{s}\) to travel from one end of the bar to the other. What is Young's modulus for this metal?

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