/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 96 Four sound waves are to be sent ... [FREE SOLUTION] | 91Ó°ÊÓ

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Four sound waves are to be sent through the same tube of air, in the same direction: $$ \begin{aligned} &s_{1}(x, t)=(9.00 \mathrm{~nm}) \cos (2 \pi x-700 \pi t) \\ &s_{2}(x, t)=(9.00 \mathrm{~nm}) \cos (2 \pi x-700 \pi t+0.7 \pi) \\ &s_{3}(x, t)=(9.00 \mathrm{~nm}) \cos (2 \pi x-700 \pi t+\pi) \\ &s_{4}(x, t)=(9.00 \mathrm{~nm}) \cos (2 \pi x-700 \pi t+1.7 \pi) . \end{aligned} $$ What is the amplitude of the resultant wave? (Hint: Use a phasor diagram to simplify the problem.)

Short Answer

Expert verified
The amplitude of the resultant wave is 14.562 nm.

Step by step solution

01

Express each wave as a phasor

The given sound waves can be expressed in phasor (complex number) form. Each wave's amplitude is represented as a vector (phasor) in the complex plane with the given phase angle:\[\begin{align*}s_1 & : 9.00 \ e^{i 0} = 9.00 s_2 & : 9.00 \ e^{i 0.7\pi} = 9.00 (\cos(0.7\pi) + i \sin(0.7\pi)) s_3 & : 9.00 \ e^{i \pi} = 9.00 (\cos(\pi) + i \sin(\pi)) s_4 & : 9.00 \ e^{i 1.7\pi} = 9.00 (\cos(1.7\pi) + i \sin(1.7\pi))\end{align*}\]
02

Calculate the real and imaginary parts for each phasor

Calculate the real (cosine) and imaginary (sine) parts of each phasor:\[\begin{align*}s_1 & : \text{real} = 9.00, \text{imaginary} = 0 s_2 & : \text{real} = 9.00 \cos(0.7\pi), \text{imaginary} = 9.00 \sin(0.7\pi) s_3 & : \text{real} = 9.00 \cos(\pi), \text{imaginary} = 9.00 \sin(\pi) s_4 & : \text{real} = 9.00 \cos(1.7\pi), \text{imaginary} = 9.00 \sin(1.7\pi)\end{align*}\]
03

Sum the real parts of the phasors

Calculate the sum of the real components of each phasor:\[\begin{align*}&= 9.00 + 9.00\cos(0.7\pi) + 9.00\cos(\pi) + 9.00\cos(1.7\pi) \&= 9.00 + 9.00(-0.809) + 9.00(-1) + 9.00(-0.809) \&= 9.00 - 7.281 - 9.00 - 7.281 \&= -14.562\end{align*}\]
04

Sum the imaginary parts of the phasors

Calculate the sum of the imaginary components of each phasor:\[\begin{align*}&= 0 + 9.00\sin(0.7\pi) + 9.00\sin(\pi) + 9.00\sin(1.7\pi) \&= 0 + 9.00(0.588) + 9.00(0) + 9.00(-0.588) \&= 5.292 + 0 - 5.292 \&= 0\end{align*}\]
05

Calculate the amplitude of the resultant wave

Use the results from the real and imaginary sums to find the resultant wave's amplitude. The amplitude is the magnitude of the resultant phasor:\[\text{Amplitude} = \sqrt{(-14.562)^2 + (0)^2} = \sqrt{211.973} = 14.562\, \text{nm}\]

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Key Concepts

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

wave interference
Wave interference occurs when two or more waves overlap, causing their effects to either strengthen or weaken each other. This phenomenon can lead to either constructive or destructive interference. In constructive interference, the waves align such that their amplitudes add up, creating a wave of greater amplitude.
Destructive interference, on the other hand, occurs when the waves are out of phase, resulting in a reduction in overall amplitude as they cancel each other out.

These interactions are not limited to sound waves but apply to all types of waves, including light and water waves. Understanding wave interference is crucial in a range of scientific and engineering fields, as it affects how waves propagate and interact in various mediums.
sound wave superposition
Superposition is a fundamental principle of waves, which states that when two or more waves meet, their overlapping effect is the sum of the individual wave effects. For sound waves, this principle is essential to understand phenomena like beats and noise cancellation.

Sound wave superposition is particularly interesting because it allows for the interference patterns that we can observe or measure. It's this principle that explains why we sometimes hear louder sounds at certain points and softer sounds at others when standing between two speakers playing the same tone.

When analyzing wave problems, it's essential to apply the superposition principle to predict how multiple sound waves will interact, whether it's for music production or designing room acoustics.
resultant wave amplitude
The resultant wave amplitude is the amplitude of a single wave that forms when multiple waves interfere with each other. It's found by combining the amplitudes and phases of individual waves. The process involves calculating the algebraic sum of the waves using phasor mathematics, which simplifies the addition of sine waves.

The resultant amplitude can tell us about the strength and intensity of the combined wave. In engineering, understanding the resultant amplitude is crucial for designing systems where wave interactions occur, such as sonar and acoustic engineering.

Mathematically, if you have the complex representations of waves, you can sum all real components and imaginary components separately and then use the Pythagorean theorem to get the resultant amplitude.
phasor diagram
A phasor diagram is a graphical representation used in phasor algebra to simplify the addition of wave forms, particularly sinusoidal waveforms with different phases.

In a phasor diagram, each wave is represented as a vector (or phasor) in the complex plane. The length of the vector represents the amplitude of the wave, while the angle corresponds to the wave's phase. By visually summing these vectors, you can easily determine the resultant wave's amplitude and phase.
  • Phasors are incredibly helpful because they convert complex mathematical problems into simple geometric exercises.
  • They are particularly used in electronics and telecommunications to analyze alternating current circuits.
Using phasor diagrams, students can better grasp how waves combine and affect each other, which is invaluable for solving problems related to wave superposition and interference.

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Most popular questions from this chapter

Two trains are traveling toward each other at \(30.5 \mathrm{~m} / \mathrm{s}\) relative to the ground. One train is blowing a whistle at \(500 \mathrm{~Hz}\). (a) What frequency is heard on the other train in still air? (b) What frequency is heard on the other train if the wind is blowing at \(30.5 \mathrm{~m} / \mathrm{s}\) toward the whistle and away from the listener? (c) What frequency is heard if the wind direction is reversed?

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