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At a certain point, two waves produce pressure variations given by \(\Delta p_{1}=\Delta p_{m} \sin \omega t\) and \(\Delta p_{2}=\Delta p_{m} \sin (\omega t-\phi) .\) At this point, what is the ratio \(\Delta p_{r} / \Delta p_{m},\) where \(\Delta p_{r}\) is the pressure amplitude of the resultant wave, if \(\phi\) is (a) \(0,\) (b) \(\pi / 2,\) (c) \(\pi / 3\), and (d) \(\pi / 4 ?\)

Short Answer

Expert verified
(a) 2, (b) \(\sqrt{2}\), (c) \(\sqrt{3}\), (d) \(\sqrt{2+\sqrt{2}}\).

Step by step solution

01

Understanding the Pressure Waves

We are given two pressure variations: \( \Delta p_{1} = \Delta p_{m} \sin(\omega t) \) and \( \Delta p_{2} = \Delta p_{m} \sin(\omega t - \phi) \). These represent the pressure amplitude of two waves at a certain point in time.
02

Resultant Pressure Amplitude Formula

The resultant pressure amplitude \( \Delta p_{r} \) can be found using the formula for the superposition of two sine waves: \[ \Delta p_{r} = \sqrt{(\Delta p_{1} + \Delta p_{2})^2} = \Delta p_{m} \sqrt{2 + 2\cos(\phi)}. \]
03

Calculating the Ratio for \( \phi = 0 \)

For \( \phi = 0 \), the formula becomes: \[ \Delta p_{r} = \Delta p_{m} \sqrt{2 + 2\cos(0)} = \Delta p_{m} \sqrt{4} = 2\Delta p_{m}. \] The ratio \( \Delta p_{r} / \Delta p_{m} = 2. \)
04

Calculating the Ratio for \( \phi = \pi/2 \)

For \( \phi = \pi/2 \), the formula becomes: \[ \Delta p_{r} = \Delta p_{m} \sqrt{2 + 2\cos(\pi/2)} = \Delta p_{m} \sqrt{2} = \sqrt{2} \Delta p_{m}. \] The ratio \( \Delta p_{r} / \Delta p_{m} = \sqrt{2}. \)
05

Calculating the Ratio for \( \phi = \pi/3 \)

For \( \phi = \pi/3 \), we have \[ \Delta p_{r} = \Delta p_{m} \sqrt{2 + 2\cos(\pi/3)} = \Delta p_{m} \sqrt{3}. \] Thus, the ratio \( \Delta p_{r} / \Delta p_{m} = \sqrt{3}. \)
06

Calculating the Ratio for \( \phi = \pi/4 \)

For \( \phi = \pi/4 \), the formula becomes: \[ \Delta p_{r} = \Delta p_{m} \sqrt{2 + 2\cos(\pi/4)} = \Delta p_{m} \sqrt{2 + \sqrt{2}}. \] Therefore, the ratio \( \Delta p_{r} / \Delta p_{m} = \sqrt{2 + \sqrt{2}}. \)

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Key Concepts

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

pressure amplitude
Pressure amplitude is a crucial concept in understanding wave behavior, particularly when dealing with two interacting waves. In this context, pressure amplitude refers to the maximum change in pressure caused by a wave at a certain point. For a single wave, this is represented by the variable \( \Delta p_m \), which denotes the maximum extent of pressure variations from the mean atmospheric pressure.

When dealing with multiple waves, such as in the exercise, we look at how these individual amplitudes combine to create a resultant wave. Typically, when two waves intersect, their pressure amplitudes can interfere in different ways, which is highly dependent on their phase relationship. This interference can either amplify or diminish the resultant pressure wave. Understanding how to calculate the pressure amplitude of the resultant wave helps predict how physical systems will behave when subject to various wave patterns. This calculation is often explored using formulas derived from fundamental principles of wave superposition.
resultant wave
The concept of a resultant wave is at the heart of wave superposition, which describes how two or more waves interact to form a new wave pattern. In the scenario provided by the original exercise, two sine waves combine to form a single resultant wave with its distinctive pressure amplitude.

To find the pressure amplitude of this resultant wave, we use the formula: \[ \Delta p_{r} = \Delta p_{m} \sqrt{2 + 2\cos(\phi)}. \]This equation takes into account both the individual contributions from each wave and their phase difference \( \phi \). By evaluating the pressure amplitude of the resultant wave, we can better understand how overlapping waves impact systems, such as sound waves in the air or pressure waves in a fluid. These insights are important for many practical applications, including audio engineering, sonar technology, and even medical imaging using ultrasound.
phase difference
Phase difference \(\phi\) is a critical factor in determining how multiple waves interfere with each other. Simply put, it is the difference in the phase angle of two waves as they interact at a single point in space.

Phase difference affects how the waves' pressure amplitudes combine. If the phase difference is zero \((\phi = 0)\), the waves are in phase, and their amplitudes add constructively, maximizing the resultant amplitude. Conversely, if the waves are out of phase by \(\phi = \pi\), they cancel each other out to a degree, potentially resulting in a lower resultant amplitude.

In the exercise, different values of \(\phi\) (such as \(0\), \(\pi/2\), \(\pi/3\), and \(\pi/4\)) show how the resultant wave's amplitude shifts, demonstrating phenomena like constructive and destructive interference. This helps illustrate why understanding phase differences is essential in fields like acoustics, telecommunications, and optics, where managing wave interactions is crucial for system performance.
sine waves
Sine waves are fundamental to the study of waves and oscillations. A sine wave is a mathematical curve that describes a smooth periodic oscillation. In context, pressure variations in the exercise are represented by sinusoidal functions such as \(\Delta p_{1} = \Delta p_{m} \sin(\omega t)\).

Sine waves are essential because they provide a simple yet accurate way to represent periodic phenomena like sound waves, light waves, and electronic signals. They also make it easy to apply mathematical techniques like superposition to analyze wave interactions. Heartbeats, radio waves, and even ocean waves can be modeled as sine waves, making them a versatile tool across different domains.

Understanding how to manipulate and interpret sine waves allows one to predict the outcome of wave interactions, as seen in the resultant amplitude calculations for different phase differences. Their mathematical elegance simplifies complex wave behavior into manageable equations, which can be used to develop technologies and solutions in engineering, physics, and beyond.

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Most popular questions from this chapter

A bat is flitting about in a cave, navigating via ultrasonic bleeps. Assume that the sound emission frequency of the bat is \(39000 \mathrm{~Hz}\). During one fast swoop directly toward a flat wall surface, the bat is moving at 0.025 times the speed of sound in air. What frequency does the bat hear reflected off the wall?

What is the bulk modulus of oxygen if \(32.0 \mathrm{~g}\) of oxygen occupies \(22.4 \mathrm{~L}\) and the speed of sound in the oxygen is \(317 \mathrm{~m} / \mathrm{s} ?\)

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Hot chocolate effect. Tap a metal spoon inside a mug of water and note the frequency \(f_{i}\) you hear. Then add a spoonful of powder (say, chocolate mix or instant coffee) and tap again as you stir the powder. The frequency you hear has a lower value \(f_{s}\) because the tiny air bubbles released by the powder change the water's bulk modulus. As the bubbles reach the water surface and disappear, the frequency gradually shifts back to its initial value. During the effect, the bubbles don't appreciably change the water's density or volume or the sound's wavelength. Rather, they change the value of \(d V / d p-\) that is, the differential change in volume due to the differential change in the pressure caused by the sound wave in the water. If \(f_{s} / f_{i}=0.333,\) what is the ratio \((d V / d p)_{s} /(d V / d p)_{i} ?\)

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