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A person hears a pure tone in the 500 to 1000 -Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point \(0.28 \mathrm{~m}\) farther from one source than the other. What is the frequency of the sound?

Short Answer

Expert verified
The frequency of the sound is 612.5 Hz.

Step by step solution

01

Understand the Problem

The problem involves finding the frequency of a sound wave produced by two sources, where the sound is loudest at points equidistant from both and minimal at a point farther from one source by a specific distance (0.28 m). This indicates destructive interference at the point of minimal sound.
02

Destructive Interference Condition

For destructive interference to occur, the path difference between the two sources should be an odd multiple of half-wavelengths, \(n + \frac{1}{2}\)\(\lambda\). Here, the path difference is given as 0.28 m.
03

Relate Wavelength and Frequency

Using the relationship between speed, frequency, and wavelength, \(v = f \lambda\), where \(v = 343 \text{ m/s}\) (speed of sound in air). The frequency, \(f\), we need to find from the given path difference condition.
04

Calculate Wavelength from Path Difference

Since the minimal sound level occurs at 0.28 m path difference, we set \(n + \frac{1}{2} = \frac{0.28}{\lambda}\). To find the closest odd \(n + \frac{1}{2}=1.0\), calculate \(\lambda = \frac{2 \times 0.28}{1} = 0.56\text{ m}\).
05

Solve for Frequency

Using the speed of sound \(v = 343\text{ m/s}\) and \(\lambda = 0.56\text{ m}\), calculate the frequency \(f\): \(f = \frac{343}{0.56}\).
06

Calculate the Frequency

Compute \(f = \frac{343 \text{ m/s}}{0.56 \text{ m}} = 612.5 \text{ Hz}\).
07

Verify Frequency Within Range

Ensure that the calculated frequency (612.5 Hz) is within the given range of 500 to 1000 Hz, confirming it fits the problem constraints.

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Key Concepts

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

Destructive Interference
Destructive interference is a fascinating phenomenon that occurs when two sound waves superpose, resulting in a reduction of sound intensity. This happens because the waves are out of phase with one another and the crests of one wave align with the troughs of another. At these points, the waves cancel each other out, leading to a minimal sound level.
In our problem, destructive interference is evident at the point where the path difference between the sound waves from two sources is 0.28 m. This specific path difference corresponds with an odd multiple of half-wavelengths, which is the condition for destructive interference. It's a concept showing how differences in the traveling distance of sound waves can result in zones of quietness or reduced sound.
To apply this concept:
  • The path difference should equal \( n+\frac{1}{2} \lambda \)
  • The identified path difference is 0.28 m, indicating that the waves are positioned for maximum cancellation.
Understanding this principle is crucial for tasks involving sound waves, whether it's ensuring optimal performance in acoustically designed venues or analyzing auditory phenomena.
Frequency Calculation
Frequency calculation is a fundamental part of understanding sound waves. The frequency refers to the number of oscillations that a wave undergoes per second, measured in Hertz (Hz). When we know the speed of a wave and its wavelength, we can easily calculate the frequency.
For sound waves in air, the speed is generally around 343 m/s. Our goal is to find the frequency when given a specific path difference due to destructive interference.
Using the general relationship between wave speed, frequency, and wavelength:
  • This relationship is expressed as \(v = f \lambda \), where \(v\) is the speed of sound.
  • Solving for \(f\), or frequency, we use the previously calculated wavelength from the known path difference.
Thus, when you have both speed and wavelength, calculating frequency is straightforward and decisive for verifying values within given constraints, such as frequencies being within a specific range (500 - 1000 Hz in our scenario).
Wavelength Determination
Determining the wavelength of a sound wave is essential for solving many physics problems related to wave behavior. The wavelength is the physical distance over which the wave's shape repeats. For sound, it can be found when you have information about path differences, as seen with the concept of destructive interference.
In this exercise:
  • We use the path difference condition \( n + \frac{1}{2} = \frac{0.28}{\lambda} \) for destructive interference to find \( \lambda \).
  • By solving this equation, choosing the nearest odd multiple, such as 1 for simplicity, helps identify the wavelength efficiently.
The calculated wavelength not only supports finding frequency but also deepens understanding of how sound waves interact based on distance traveled, a fundamental part of acoustics and wave physics. This determination process is pivotal for various applications, from designing better sound systems to assessing noise impact in environments.

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Most popular questions from this chapter

At a rock concert, a dB meter registered \(130 \mathrm{~dB}\) when placed \(2.2 \mathrm{~m}\) in front of a loudspeaker on the stage. \((a)\) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air? (b) How far away would the sound level be a somewhat reasonable \(85 \mathrm{~dB} ?\)

A science museum has a display called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are open on both ends. (a) If the pipes have lengths of \(3.0 \mathrm{m}, 2.5 \mathrm{m}\) , \(2.0 \mathrm{m}, 1.5 \mathrm{m}\) and \(1.0 \mathrm{m},\) what frequencies will be heard by a visitor's ear placed near the ends of the pipes? (b) Why does this display work better on a noisy day than on a quiet day?

When a player's finger presses a guitar string down onto a fret, the length of the vibrating portion of the string is shortened, thereby increasing the string's fundamental frequency (see Fig. 16-35). The string's tension and mass per unit length remain unchanged. If the unfingered length of the string is \(\ell=65.0 \mathrm{~cm},\) determine the positions \(x\) of the first six frets, if each fret raises the pitch of the fundamental by one musical note in comparison to the neighboring fret. On the equally tempered chromatic scale, the ratio of frequencies of neighboring notes is \(2^{1 / 12}\)

Determine the fundamental and first overtone frequencies for an 8.0 -m-long hallway with all doors closed. Model the hallway as a tube closed at both ends.

The diameter \(D\) of a tube does affect the node at the open end of a tube. The end correction can be roughly approximated as adding \(D / 3\) to the effective length of the tube. For a closed tube of length \(0.60 \mathrm{~m}\) and diameter \(3.0 \mathrm{~cm},\) what are the first four harmonics, taking the end correction into consideration?

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