Chapter 11: Problem 92
A sine wave has an amplitude \(A\) and wavelength \(\lambda\) The ratio of particle velocity and the wave velocity is \((2 \pi A=\lambda)\) (a) \(\leq 1\) (b) \(=1\) (c) \(\geq 1\) (d) None of these
Short Answer
Expert verified
The ratio of particle velocity to wave velocity is 1 when \(2\pi A = \lambda\).
Step by step solution
01
Understanding the Given Data
We are provided with a sine wave characterized by an amplitude, \(A\), and a wavelength, \(\lambda\). We need to evaluate the ratio of the particle velocity to wave velocity specifically when \(2\pi A = \lambda\).
02
Defining Particle and Wave Velocities
The particle velocity \(v_p\) is the derivative of the displacement with respect to time. For a sine wave given by \(y = A \sin(kx - \omega t)\), where \(k = \frac{2\pi}{\lambda}\) and \(\omega\) is the angular frequency. The wave velocity \(v_w\) is given by \(v_w = \frac{\omega}{k} = \frac{\omega \lambda}{2\pi}\).
03
Calculating Particle Velocity
The particle velocity \(v_p\) is the time derivative of the displacement function. Differentiate \(y = A \sin(kx - \omega t)\) with respect to \(t\), which yields \( v_p = -A \omega \cos(kx - \omega t) \). The maximum particle velocity occurs when \( \cos(kx - \omega t) = \pm 1 \), giving \( |v_p|_{max} = A \omega \).
04
Substituting Given Relation
From the provided condition \(2\pi A = \lambda\), substitute this into the expression for wave velocity: \( v_w = \frac{\omega \lambda}{2\pi} = \frac{\omega \cdot 2\pi A}{2\pi} = \omega A \). Thus, \(v_w = A \omega\).
05
Evaluating the Ratio
Substitute \(v_p = A \omega \) and \(v_w = A \omega \) into the ratio: \( \text{Ratio} = \frac{v_p}{v_w} = \frac{A \omega}{A \omega} = 1 \).
06
Choosing the Correct Answer
Seeing that the ratio simplified to 1, the correct answer choice is (b) \(=1\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Particle Velocity
When discussing wave motion, it's important to understand particle velocity. This is a measure of how quickly a particular point, or particle, on the wave moves as the wave passes through it. For a sine wave, the equation of motion can be written as
- \(y = A \sin(kx - \omega t)\)
- \(v_p = -A \omega \cos(kx - \omega t)\)
Wave Velocity
Wave velocity, often represented as \(v_w\), indicates how quickly the wave propagates through the medium. For a sine wave, the formula connects the wavelength \(\lambda\) and angular frequency \(\omega\):
- \(v_w = \frac{\omega}{k} = \frac{\omega \lambda}{2\pi}\)
Sine Wave
The sine wave is a fundamental concept in understanding wave motion. It refers to a smooth periodic oscillation that is often used to model waves. This is represented mathematically as:
- \(y = A \sin(kx - \omega t)\)
Wavelength
Wavelength, denoted as \(\lambda\), is an essential property of waves. It is the distance between successive crests, troughs, or identical points in consecutive cycles of a wave. In a sine wave, the wavelength determines how 'stretched' the wave appears:
- A higher wavelength means a broader wave, while a smaller wavelength means a more compressed wave.
- \(\text{Wave Speed} = \text{Frequency} \times \text{Wavelength}\)
Amplitude
Amplitude is a measure of the wave's energy and determines the height of the wave. For a sine wave, amplitude \(A\) indicates the maximum extent of a wave’s oscillation from its resting position. It measures how 'loud' a sound wave is or how 'bright' a light wave appears:
- Greater amplitude indicates more energy in the wave.
- It is symmetrically distributed on both sides of the central axis of the wave.