18. Waves & Sound

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?]-

Unpolarized light of initial intensity $I_0$ passes through two ideal polarizers. The transmission axis of the first polarizer is vertical, and the second is oriented at an angle $\theta$ with respect to the vertical. What is the intensity $I_2$ of the light after passing through both polarizers?

Which best describes how wave $I$ntensity and $L$oudness are typically related?

Which term describes the height of a sound wave?

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?

(II) What is the ratio of the amplitudes of an earthquake P wave passing through the Earth and detected at two points 15 km and 55 km from the source?

How does increasing the amplitude of a sound wave affect the volume (loudness) of the sound?

Which of the following changes would result in an increase in $I$ (wave intensity)?

Which property of a light wave determines its brightness?

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?

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/m². An intensity of 1.0 W/m² is often used as the 'threshold of pain.' How much closer to the source can you move before the sound intensity reaches this threshold?

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. What is the amplitude of the wave?

A jet plane at takeoff can produce sound of intensity 10.0 W/m² at 30.0 m away. But you prefer the tranquil sound of normal conversation, which is 1.0 μW/m². 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?

What is the ratio of the intensities, of an earthquake P wave passing through the Earth and detected at two points 15 km and 55 km from the source?