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Ch 16: Traveling Waves
Chapter 16, Problem 16

What are the sound intensity levels for sound waves of intensity (a) 3.0 x 10⁻⁶ W/m²?

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Identify the formula to calculate the sound intensity level (SIL) in decibels (dB). The formula is: \( SIL = 10 \log_{10} \left(\frac{I}{I_0}\right) \), where \( I \) is the intensity of the sound wave and \( I_0 \) is the reference intensity, typically \( 1.0 \times 10^{-12} \, W/m^2 \).
Substitute the given intensity \( I = 3.0 \times 10^{-6} \, W/m^2 \) into the formula.
Use the reference intensity \( I_0 = 1.0 \times 10^{-12} \, W/m^2 \) in the formula.
Calculate the ratio \( \frac{I}{I_0} \) by dividing the given intensity by the reference intensity.
Compute \( 10 \log_{10} \left(\frac{I}{I_0}\right) \) to find the sound intensity level in decibels (dB).

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Key Concepts

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

Sound Intensity

Sound intensity is defined as the power per unit area carried by a sound wave. It is measured in watts per square meter (W/m²) and quantifies how much sound energy passes through a given area in a specific time. Higher intensity levels correspond to louder sounds, while lower levels indicate quieter sounds.
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Decibel Scale

The decibel (dB) scale is a logarithmic scale used to measure sound intensity levels. It expresses the ratio of a particular sound intensity to a reference intensity, typically the threshold of hearing (1 x 10⁻¹² W/m²). The formula to convert intensity (I) to decibels is L = 10 log10(I/I₀), where I₀ is the reference intensity.
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Threshold of Hearing

The threshold of hearing is the minimum sound intensity level that the average human ear can detect, approximately 1 x 10⁻¹² W/m². This reference point is crucial for calculating sound intensity levels in decibels, as it allows for a standardized comparison of different sound intensities relative to what humans can perceive.
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Related Practice
Textbook Question
FIGURE P16.57 shows a snapshot graph of a wave traveling to the right along a string at 45 m/s. At this instant, what is the velocity of points 1, 2, and 3 on the string?

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The string in FIGURE P16.59 has linear density μ. Find an expression in terms of M, μ, and θ for the speed of waves on the string.

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FIGURE EX16.8 is a picture at t = 0 s of the particles in a medium as a longitudinal wave is passing through. The equilibrium spacing between the particles is 1.0 cm. Draw the snapshot graph D(x, t = 0 s) of this wave at t = 0 s.

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Textbook Question
Show that the displacement D(x,t) = cx² + dt², where c and d are constants, is a solution to the wave equation. Then find an expression in terms of c and d for the wave speed.
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Textbook Question
A sound wave is described by D (y,t) = (0.0200 mm) ✕ sin [(8.96 rad/m)y + (3140 rad/s)t + π/4 rad], where y is in m and t is in s. b. Along which axis is the air oscillating?
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Textbook Question
One cue your hearing system uses to localize a sound (i.e., to tell where a sound is coming from) is the slight difference in the arrival times of the sound at your ears. Your ears are spaced approximately 20 cm apart. Consider a sound source 5.0 m from the center of your head along a line 45° to your right. What is the difference in arrival times? Give your answer in microseconds. Hint: You are looking for the difference between two numbers that are nearly the same. What does this near equality imply about the necessary precision during intermediate stages of the calculation?

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