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PHYSICS Mr. BALDWIN WAVES 5-Feb-14

PHYSICS Mr. BALDWIN WAVES 5-Feb-14. AIM: How do you know a fire engine is coming towards you? (What is the Doppler Effect?) DO NOW: Describe what you observe as a siren approached you and when it goes away from you. TURN IN Y our ESSAY on the Doppler Effect

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PHYSICS Mr. BALDWIN WAVES 5-Feb-14

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  1. PHYSICS Mr. BALDWIN WAVES 5-Feb-14 AIM: How do you know a fire engine is coming towards you? (What is the Doppler Effect?) DO NOW: Describe what you observe as a siren approached you and when it goes away from you. TURN IN • Your ESSAY on the Doppler Effect • Completed Worksheets 20.1 & 21.1

  2. Velocity of Sound • How are sound waves produced? • Most sound are produced by vibrating objects, such as a vibrating cone of a loud speaker. • Speed of sound depends on temperature (0C) • CHECK…What is the speed of sound at 200C? • Speed of sound at standard temperature & pressure (STP - 200C & 1atm) vsound = 343 m/s

  3. The Doppler Effect • The apparent change in the observed frequency of a wave between a moving source and observer.

  4. It is applicable to any type of wave. • Austrian physicist Christian Doppler (1803-1853). train sound clip Simulations • physlet animation • http://www.walter-fendt.de/ph14e/dopplereff.htm

  5. Analyze this. • If the observer & source is moving apart, vs is positive • If the observer & source is moving closer, vs is negative • The velocity of sound is about 340 m/s. What are the frequencies observed as a fire engine, with siren blaring at 200Hz and moving at 17 m/s, approaches and then passes you?

  6. DO IT YOURSELF An ambulance is approaching a stationary observer. The siren of the ambulance emits a frequency of 480Hz and the speed of the ambulance is 50km/h(=13.88m/s). What wavelength and frequency will the stationary observer hear when the ambulance is approaching? Assume T=20oC.

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