# Chapter 14 Sound AP Physics B Lecture Notes.

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Chapter 14 Sound AP Physics B Lecture Notes

Sound Sections Producing a Sound Wave Characteristics of Sound Waves The Speed of Sound Spherical and Plane Waves The Doppler Effect Interference of Sound Waves Standing Waves Standing Waves in Air Columns Beats

Producing a Sound Wave

Characteristics of Sound Waves Characteristics of Sound
Loudness: related to intensity of the sound wave Loudness: related to intensity of the sound wave Pitch: related to frequency Pitch: related to frequency Audible range: about 20 Hz to 20,000 Hz Audible range: about 20 Hz to 20,000 Hz Ultrasound: above 20,000 Hz Ultrasound: above 20,000 Hz Infrasound: below 20 Hz Infrasound: below 20 Hz Phy 2054 Lecture Notes 12

Chapter 14 Sound The pitch of a musical note is characterized by the sound’s (A) amplitude (B) frequency (C) wavelength (D) speed

The Speed of Sound Sound can travel through any kind of matter, but not through a vacuum. Sound can travel through any kind of matter, but not through a vacuum. The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids. The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids. The speed depends somewhat on temperature, especially for gases. The speed depends somewhat on temperature, especially for gases.

Chapter 14 Sound Which of the following is a true statement? (A) Sound waves are transverse pressure waves. (B) Sound waves can not travel through a vacuum. (C) Sound waves and light waves travel a the same speed. (D) When the frequency of a sound wave increases its wavelength also increases.

The Speed of Sound Speed of a wave on a string. Speed of sound in a fluid. Speed of sound in a solid. Speed of sound in air is temperature dependent.

Chapter 14 Sound As the temperature of the air increases, the speed of sound through the air (A) increases. (B) decreases. (C) does not change. (D) increases if the atmospheric pressure is high.

Chapter 14 Sound Sound of a frequency f travels through air with a wavelength l. If the frequency of the sound is increased to 2f, its wavelength in air will be

Spherical and Plane Waves
The intensity of sound from a point source diminishes with distance: Phy 2054 Lecture Notes 12

Chapter 14 Sound The intensity of a point source at a distance d from the source is I. The intensity of the sound at a distance 2d from the source?

Chapter 14 Sound The intensity of a sound increases when there is an increase in the sound’s (A) frequency (B) wavelength (C) amplitude (D) speed

The Doppler Effect "I love hearing that lonesome wail of the train whistle as the magnitude of the frequency of the wave changes due to the Doppler effect." Phy 2054 Lecture Notes 12

The Doppler Effect The Doppler Effect for two stationary observers

The Doppler Effect The Doppler effect occurs when a source of sound is moving with respect to an observer. Stationary truck Longer wavelength Lower frequency Shorter wavelength Higher frequency Moving truck Phy 2054 Lecture Notes 12

The Doppler Effect is experienced whenever there is
relative motion between the sound source and an observer. Doppler Effect Phy 2054 Lecture Notes 12

The Doppler Effect Stationary Source Higher Frequency Stationary
Observer Higher Frequency Phy 2054 Lecture Notes 12

The Doppler Effect Stationary Source Lower Frequency Stationary
Observer Lower Frequency Phy 2054 Lecture Notes 12

The Doppler Effect Phy 2054 Lecture Notes 12

Chapter 14 Sound A police car with its siren on departs from a stationary observer. The frequency heard by the observer (A) is higher than the source. (B) is lower than the source. (C) is the same as that of the source. (D) is equal to zero.

The Doppler Effect (problem)
You are standing still. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s a) toward you? b) away from you? Phy 2054 Lecture Notes 12

The Doppler Effect (Problem)
A bat flies toward a wall at a speed of 5.0 m/s. As it flies, the bat emits an ultrasonic sound wave with a frequency of 30.0 kHz. What frequency does the bat hear in the reflected wave? Phy 2054 Lecture Notes 12

Interference of Sound Waves
Sound waves interfere in the same way that other waves do in space.

Sources of Sound: Vibrating Strings and Air Columns
Standing Waves Sources of Sound: Vibrating Strings and Air Columns Musical instruments produce sounds in various ways – vibrating strings vibrating membranes vibrating metal or wood shapes vibrating air columns Musical instruments produce sounds in various ways – vibrating strings vibrating membranes vibrating metal or wood shapes vibrating air columns The vibration may be started by: plucking striking bowing blowing The vibration may be started by: plucking striking bowing blowing The vibrations are transmitted to the air and then to our ears. The vibrations are transmitted to the air and then to our ears. Phy 2054 Lecture Notes 12

Standing Waves The strings on a guitar can be effectively shortened by fingering, raising the fundamental pitch. The strings on a guitar can be effectively shortened by fingering, raising the fundamental pitch. The pitch of a string of a given length can also be altered by using a string of different density. The pitch of a string of a given length can also be altered by using a string of different density. Standing Waves Phy 2054 Lecture Notes 12

First Harmonic - Fundamental
Standing Waves First Harmonic - Fundamental Second Harmonic Third Harmonic Phy 2054 Lecture Notes 12

Chapter 14 Sound The standing wave on a vibrating guitar string produces a sound wave in the air. The two waves have (A) the same wavelength. (B) the same speed. (C) the same frequency. (D) the same amplitude.

Standing Waves in Air Columns
A tube open at both ends has displacement antinodes, at the ends. L First Harmonic - Fundamental Second Harmonic Third Harmonic Phy 2054 Lecture Notes 12

Chapter 14 Sound A pipe open at both ends resonates with a fundamental frequency of 150 Hz. Which one of the following frequencies will not resonate in this pipe (A) 300 Hz (B) 450 Hz (C) 500 Hz (D) 750 Hz

Standing Waves in Air Columns (Problem)
A uniform narrow tube 1.8 m long is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What is the speed of sound in the gas in the tube? Phy 2054 Lecture Notes 12

Standing Waves in Air Columns
A tube closed at one end has a displacement node at the closed end. L First Harmonic - Fundamental Third Harmonic Fifth Harmonic Phy 2054 Lecture Notes 12

Chapter 14 Sound A pipe open at one end and closed at the other end. resonates with a fundamental frequency of 150 Hz. Which one of the following frequencies will not resonate in this pipe (A) 300 Hz (B) 450 Hz (C) 760 Hz (D) 1050 Hz

Standing Waves in Air Columns

Beats Beat Frequency

Chapter 12 Sound The interference of two sound waves can produces a beat frequency if the waves have (A) the same amplitude. (B) slightly different amplitudes. (C) the same frequency. (D) slightly different frequencies.

Chapter 12 Sound Two pure tones are sounded together and a particular beat frequency is heard. If the frequency of one of the tones is decreased slightly, the beat frequency (A) will increases. (B) will decreases. (C) does not change. (D) could either increase or decrease.

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