Chapter 3: Problem 11
Sketch the graph of the harmonic wave \(\phi(x, t)=\sin 2 \pi(x-t)\) as a function of \(x(-1 \leq x \leq 2)\) for values of time \(t\), (i) \(t=0\), (ii) \(t=1 / 4\), (iii) \(t=1 / 2\).
Short Answer
Expert verified
Plot the sine wave for each given \( t \) value, adjusting position and shape accordingly.
Step by step solution
01
Understand the Wave Function
The given wave function is \( \phi(x, t) = \sin 2\pi(x-t) \). It's important to identify that this function represents a wave traveling along the x-axis, where \( x \) is the position and \( t \) is the time. The argument of the sine function, \( 2\pi(x - t) \), indicates a wave with a period of 1.
02
Plot for t=0
Substitute \( t = 0 \) into the wave function: \( \phi(x, 0) = \sin 2\pi x \). This is a standard sine wave with a wavelength of 1, which means it completes one full cycle over the interval from 0 to 1. Plot this wave for \( x \) from -1 to 2, considering one full cycle over every interval of length 1.
03
Plot for t=1/4
Substitute \( t = 1/4 \) into the wave function: \( \phi(x, 1/4) = \sin 2\pi(x - 1/4) = \sin (2\pi x - \pi/2) \). This represents the original wave shifted to the right by 1/4 of its cycle. Adjust the plot of \( \sin 2\pi x \) to start at \( x = 1/4 \) and end at \( x = 1.25 \) over one complete cycle.
04
Plot for t=1/2
Substitute \( t = 1/2 \) into the wave function: \( \phi(x, 1/2) = \sin 2\pi(x - 1/2) = \sin (2\pi x - \pi) \). This corresponds to the wave being shifted to the right by 1/2 of its cycle or a half-wavelength. Effectively, this is the same as reflecting the wave: \( \phi(x, 1/2) = -\sin 2\pi x \), resulting in an inverted wave with peaks where there were troughs.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Wave Function
Understanding the concept of a wave function is key to analyzing harmonic waves. A wave function, such as \[ \phi(x, t) = \sin 2\pi(x-t) \]especially in the context of harmonic waves, is a mathematical description that tells us the displacement of the wave at any given point in space and time. Here,
- \(x\): represents the position along the wave's path.
- \(t\): represents the time, showing how the wave evolves over time.
- \(\sin\): indicates the type of wave, which in this case is sinusoidal or a sine wave.
Sine Wave
A sine wave is one of the most fundamental types of waveforms. It is characterized by its smooth, repetitive oscillation. The wave function given \\( \phi(x, t) = \sin 2\pi(x-t) \) is an example of a sine wave, which naturally occurs in various physical phenomena such as sound waves, light waves, and water waves.
- Properties: Sine waves have a distinct wave pattern, where they begin at zero, rise to a peak, descend through zero to a trough, and then return to zero, completing one full cycle.
- Cycle: A single cycle refers to the wave moving through one complete oscillation, standardly defined from 0 to 2\(\pi\) for the sine function, before repeating again.
- Amplitude: The maximum height reached by the wave from its central axis. For the function \( \sin 2\pi(x-t) \), the amplitude is 1, indicating the wave's peaks occur at \(\pm 1\).
Wave Period
The wave period is a critical concept when analyzing periodic waves, like the sine waves described by our wave function \[ \phi(x, t) = \sin 2\pi(x-t) \].The period of a wave is the distance over which the wave's shape repeats, and it is inversely related to frequency.
- Definition: It can be seen as the horizontal length required to complete one full wave cycle.
- Calculation: For our function, since the argument is \(2\pi(x-t)\), the wave completes one cycle for every unit interval of \(x\), giving a period of 1.
- Implication: A period of 1 means that as \(x\) advances from 0 to 1, the wave transitions through its complete pattern from crest to trough and back to crest.
Wave Shift
Wave shift is an essential concept for understanding changes in a wave's position over time. It describes how a wave can move horizontally along its axis. In the context of the wave function \[ \phi(x, t)=\sin 2\pi(x-t) \], various shifts occur as the time \(t\) changes.
- General Definition: A phase shift occurs when the graph of the sine wave slides left or right by a certain amount, without altering its shape.
- Example at \(t=1/4\): Substituting \(t=1/4\) results in a wave function \(\phi(x, 1/4) = \sin (2\pi x - \pi/2)\), showing a shift to the right by 1/4 of the cycle, equivalent to \(\pi/2\) in the sine function's phase.
- Example at \(t=1/2\): For \(t=1/2\), the function becomes \(\phi(x, 1/2) = -\sin 2\pi x\), indicating a half-cycle shift or phase shift, which mirrors the wave across the x-axis.