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A sinusoidal sound wave is described by the displacement wave function $$ s(x, t)=(2.00 \mu \mathrm{m}) \cos \left[\left(15.7 \mathrm{m}^{-1}\right) x-\left(858 \mathrm{s}^{-1}\right) t\right] $$ (a) Find the amplitude, wavelength, and speed of this wave. (b) Determine the instantaneous displacement from equilibrium of the elements of air at the position \(x=0.0500 \mathrm{m}\) at \(t=3.00 \mathrm{ms}\) . (c) Determine the maximum speed of the element's oscillatory motion.

Short Answer

Expert verified
The amplitude is 2.00 micrometers, the wavelength is \( \frac{2\pi}{15.7} \) meters, and the speed is \( \frac{2\pi}{15.7} \) times \( \frac{858}{2\pi} \) meters per second. The instantaneous displacement at x=0.0500 m and t=3.00 ms is \( s(0.0500, 0.00300) \). The maximum speed is the amplitude times the angular frequency.

Step by step solution

01

Identify the Amplitude

To find the amplitude of the wave, look at the coefficient in front of the cosine function in the wave function. This coefficient represents the maximal displacement from the equilibrium position and is given directly by the wave function as the amplitude.
02

Find the Wavelength

The wavelength can be determined from the wave number, which is the coefficient of x inside the cosine function. The wave number k is related to the wavelength lambda by the equation \( k = \frac{2\pi}{\lambda} \). Solving for the wavelength \( \lambda \), we get \( \lambda = \frac{2\pi}{k} \).
03

Calculate the Speed of the Wave

The speed of the wave can be found by using the relationship between wave speed v, wavelength \( \lambda \), and frequency f, which is \( v = \lambda f \). From the given information, we can deduce the angular frequency \( \omega = 858 \, \mathrm{s}^{-1} \) which is related to the frequency by \( f = \frac{\omega}{2\pi} \). Then we can calculate the speed of the wave.
04

Determine Instantaneous Displacement

To find the instantaneous displacement at a specific position x and time t, we plug these values into the wave function \( s(x, t) \) to get the specific displacement from equilibrium for the elements of air.
05

Find the Maximum Speed of Oscillatory Motion

The maximum speed of the oscillatory motion happens when the cosine function in the velocity equation, which is the derivative of the displacement function, equals 1 or -1. We calculate the derivative of the displacement to get the velocity, and then find the maximum.

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Key Concepts

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

Wave Amplitude
Wave amplitude is a crucial concept in understanding sinusoidal sound waves. It represents the maximum displacement of particles from their equilibrium position as the wave passes. In the context of our exercise, the amplitude is given directly by the coefficient in front of the cosine function in the displacement wave equation, which is \(2.00 \mu m\). This value indicates the peak height of the wave鈥攖he higher the amplitude, the louder the sound we perceive. Understanding amplitude is essential for analyzing sound waves, as it affects the energy carried by the wave and, consequently, its intensity.

Wavelength Calculation
The wavelength (\(\lambda\)) of a wave is the distance between two successive points that are in phase, such as two consecutive crests or troughs. In the provided exercise, the wavelength is calculated by using the wave number (\(k\)), which is given as \(15.7 \mathrm{m}^{-1}\). Using the relationship \(k = \frac{2\pi}{\lambda}\), we isolate \(\lambda\) to find \(\lambda = \frac{2\pi}{k}\). This formula is invaluable for understanding the spatial characteristic of sound waves and determines how they interact with objects and environments.

Wavelength and Wave Number

Remember that the wave number is inversely proportional to the wavelength鈥攖he larger the wave number, the smaller the wavelength. Wavelength affects the pitch of the sound, with shorter wavelengths corresponding to higher pitches.
Wave Speed
Wave speed is indicative of how fast the wave travels through the medium. In sound waves, this speed depends on the medium's properties and the wave's frequency and wavelength. Using the relationship \(v = \lambda f\), where \(v\) is the speed of the wave, and \(f\) is the frequency, we can determine the wave's speed. For our exercise, the angular frequency given allows us to calculate the frequency with \(f = \frac{\omega}{2\pi}\), and hence the wave speed. Knowing the speed of sound in different media is critical for applications ranging from medical ultrasound to architectural acoustics.

Instantaneous Displacement
Instantaneous displacement refers to the specific position of a particle at an exact moment in time as the wave passes through it. For a sinusoidal wave, this displacement varies over time and position. In the exercise, substituting given values of \(x\) and \(t\) into the wave function \(s(x, t)\) yields the instantaneous displacement. This concept is vital in understanding how particles in the medium move as the wave propagates. It's a snapshot of the wave's impact on the particle at any given instance.

Oscillatory Motion Speed
The maximum speed of oscillatory motion for elements within a wave occurs when the particle's velocity is at its peak. It happens when the derivative of the displacement function with respect to time, which gives us velocity, equals its maximum value. In practice, this is when the cosine part of the velocity equation is either 1 or -1 (depending on the direction of motion). Finding this value provides insight into the dynamic behavior of particles in the medium as they respond to the wave's energy, which is especially important in analyzing vibrational motion.

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