# Lecture23 - PHYSICS 231 INTRODUCTORY PHYSICS I Lecture 23...

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PHYSICS 231 INTRODUCTORY PHYSICS I Lecture 23

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Speed of sound in fluid (for solid, replace ) Intensity Intensity Level - dB Spherical Waves Last Lecture -Sound v = B ! = 10 log 10 I I o I = I 0 10 /10 I = P 4 r 2 B " Y I = P A I 0 = 10 " 12 W/m 2
Doppler Effect, Moving Observer Fig 14.8, p. 435 Slide 12 Towards source: Away from source: ƒ' = ƒ v + v o v ! " # \$ % & = ƒ v ! v o v " # \$ % & Fig 14.9, p. 436 Slide 13 v = speed of sound, v O = speed of observer

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Doppler Effect: Source in Motion ! ' = !" v s T = v s v = 1 " v s v ( ) f ' = ' f ' = f v v ! v s " # "
Doppler Effect, Source in Motion Approaching source: Source leaving: f ' = f v v ! v s f ' = f v v + v s

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Example 14.6 An train has a brass band playing a song on a flatcar. As the train approaches the station at 21.4 m/s, a person on the platform hears a trumpet play a note at 3520 Hz. DATA: v sound = 343 m/s a) What is the true frequency of the trumpet? b) What is the wavelength of the sound? c) If the trumpet plays the same note after passing the platform, what frequency would the person on the platform hear? a) 3300 Hz b) 9.74 cm c) 3106 Hz
Fig 14.11, p. 439 Slide 15 Shock Waves (Sonic Booms) When the source velocity exceeds the speed of sound,

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Application: weather radar Both humidity (reflected intensity) and speed of clouds (doppler effect) are measured.

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Doppler Effect: Both Observer and Source Moving Switch appropriate signs if observer or source moves away ƒ' = ƒ v ± v o v ± v s !
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Lecture23 - PHYSICS 231 INTRODUCTORY PHYSICS I Lecture 23...

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