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Ch. 15 - Wave Motion
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Not the one you use?Change textbook
Chapter 15, Problem 29b

A 572-Hz longitudinal wave in air has a speed of 345 m/s. How much time is required for the phase to change by 90° at a given point in space?

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1
Determine the period of the wave using the formula for the period: T=1f, where f is the frequency of the wave (572 Hz).
Recognize that a phase change of 90° corresponds to one-quarter of a full cycle, as a full cycle corresponds to 360°.
Calculate the time required for a 90° phase change by taking one-quarter of the period: t=T4.
Substitute the value of the period T (calculated in step 1) into the equation from step 3 to find the time for the phase change.
Express the final result in seconds, ensuring the units are consistent throughout the calculation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Wave Speed

Wave speed is the rate at which a wave propagates through a medium. It is determined by the medium's properties and can be calculated using the formula v = fλ, where v is the wave speed, f is the frequency, and λ is the wavelength. In this case, the wave speed is given as 345 m/s.
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Frequency

Frequency is the number of cycles of a wave that pass a given point per unit time, measured in hertz (Hz). For the given wave, the frequency is 572 Hz, indicating that 572 cycles occur every second. This concept is crucial for understanding how quickly the wave oscillates and relates directly to the time it takes for phase changes.
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Phase Change

Phase change in a wave refers to the shift in the wave's position in its cycle, typically measured in degrees or radians. A 90° phase change corresponds to a quarter of a wavelength. To find the time required for this phase change, one can use the relationship between frequency and time, where time is the inverse of frequency, allowing for the calculation of the duration for a specific phase shift.
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