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18. Waves & Sound

Wave Intensity

18. Waves & Sound

Wave Intensity

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The Inverse-Square Law for Intensity

The Inverse-Square Law for Intensity

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Multiple Choice

A sound source radiates sound waves in all directions. At a distance of 4 m from the source, you measure the wave intensity to be 0.06 W/m². How much sound energy does the source emit in 1 hour if the power output is constant?

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Multiple Choice

You measure the intensity from a sound source to be 0.3 W/m² at a distance of 3.4 m. What will the intensity be if you walk closer to the source, to a distance of 2.5 m?

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Textbook Question

(I) Two earthquake waves of the same frequency travel through the same portion of the Earth, but one is carrying 3.5 times the energy. What is the ratio of the amplitudes of the two waves?

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Textbook Question

(II) What is the ratio of

(a) the intensities, of an earthquake P wave passing through the Earth and detected at two points 15 km and 55 km from the source?

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Textbook Question

(II) What is the ratio of

(b) the amplitudes, of an earthquake P wave passing through the Earth and detected at two points 15 km and 55 km from the source?

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Textbook Question

A bug on the surface of a pond is observed to move up and down a total vertical distance of 0.10 m, lowest to highest point, as a wave passes. (a) What is the amplitude of the wave?

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Textbook Question

A bug on the surface of a pond is observed to move up and down a total vertical distance of 0.10 m, lowest to highest point, as a wave passes. (b) If the amplitude increases to 0.15 m, by what factor does the bug’s maximum kinetic energy change?

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Textbook Question

An earthquake-produced surface wave can be approximated by a sinusoidal transverse wave. Assuming a frequency of 0.60 Hz (typical of earthquakes, which actually include a mixture of frequencies), what amplitude is needed so that objects begin to leave contact with the ground? [Hint: Set the acceleration a > g. Why?]-

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Textbook Question

Energy Output. By measurement you determine that sound waves are spreading out equally in all directions from a point source and that the intensity is 0.026 W/m^2 at a distance of 4.3 m from the source. (b) How much sound energy does the source emit in one hour if its power output remains constant?

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Textbook Question

Energy Output. By measurement you determine that sound waves are spreading out equally in all directions from a point source and that the intensity is 0.026 W/m^2 at a distance of 4.3 m from the source. (a) What is the intensity at a distance of 3.1 m from the source?

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Textbook Question

Threshold of Pain. You are investigating the report of a UFO landing in an isolated portion of New Mexico, and you encounter a strange object that is radiating sound waves uniformly in all directions. Assume that the sound comes from a point source and that you can ignore reflections. You are slowly walking toward the source. When you are 7.5 m from it, you measure its intensity to be 0.11 W/m^2. An intensity of 1.0 W/m^2 is often used as the 'threshold of pain.' How much closer to the source can you move before the sound intensity reaches this threshold?

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Textbook Question

A jet plane at takeoff can produce sound of intensity 10.0 W/m^2 at 30.0 m away. But you prefer the tranquil sound of normal conversation, which is 1.0 μW/m^2. Assume that the plane behaves like a point source of sound. (a) What is the closest dis-tance you should live from the airport runway to preserve your peace of mind? (b) What intensity from the jet does your friend experience if she lives twice as far from the runway as you do? (c) What power of sound does the jet produce at takeoff?

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Textbook Question

At a distance of 7.00x10^12 m from a star, the intensity of the radiation from the star is 15.4 W/m^2. Assuming that the star radiates uniformly in all directions, what is the total power output of the star?

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Textbook Question

The intensity of electromagnetic waves from the sun is 1.4 kW/m² just above the earth's atmosphere. Eighty percent of this reaches the surface at noon on a clear summer day. Suppose you think of your back as a 30 cm x 50 cm rectangle. How many joules of solar energy fall on your back as you work on your tan for 1.0 h?

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Textbook Question

LASIK eye surgery uses pulses of laser light to shave off tissue from the cornea, reshaping it. A typical LASIK laser emits a 1.0-mm-diameter laser beam with a wavelength of 193 nm. Each laser pulse lasts 15 ns and contains 1.0 mJ of light energy. b. During the very brief time of the pulse, what is the intensity of the light wave?

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Textbook Question

Which of the following statements is explained best using the Chargaff's rule?

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Textbook Question

A concert loudspeaker suspended high above the ground emits 35 W of sound power. A small microphone with a 1.0 cm² area is 50 m from the speaker. a. What is the sound intensity at the position of the microphone?

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Textbook Question

A sound source is located somewhere along the x-axis. Experiments show that the same wave front simultaneously reaches listeners at x = ─7.0 m and x = ＋3.0 m. a. What is the x-coordinate of the source?

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