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## Doppler Effect (Ch. 12 Sec 12 7 p.338 – 342)

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**Demo: Whirling Bell**Change in frequency of the sound from a moving object as the object moves past some observer. Doppler Effect (Ch. 12 Sec 12 7 p.338 – 342) Show Example of waves undergoing Doppler Effect**For a moving source of the sound the equation for the**stationary observed frequency is: Where: f f ‘ = observed frequency f = frequency of the source v f ‘ = v = speed of the sound Doppler Effect v+us us = speed of source + is used when source is moving away from observer - is used when source is moving towards from observer**For a moving observer the frequency of observed stationary**sound source is: Where: f f ‘ = observed frequency f = frequency of the source v+uo f ‘ = v = speed of the sound Doppler Effect v uo = speed of observer + is used when observer is moving towards the source - is used when observer is moving away from source**Example 1**Calculate the range of frequencies of an ambulance siren that holds a frequency of 330 Hz if the ambulance drives past you at 38 m/s if the speed of sound is 340 m/s? f ‘ = f ‘ = f ‘ = f ‘ = 330 Hz 371 Hz 330 Hz x 1.126 f 330 Hz x 0.8995 297 Hz v 340 m/s f ‘ = f ‘ = Doppler Effect v+us 340 +38**Example 2**Calculate the range of frequencies of an stationary ambulance siren that holds a frequency of 330 Hz if you drive by the ambulance at 38 m/s if the speed of sound is 340 m/s? f ‘ = f ‘ = f ‘ = f ‘ = 330 Hz f 293 Hz 330 Hz x 0.888 366 Hz 330 Hz x 1.112 v+uo 340 +38 f ‘ = f ‘ = Doppler Effect 340 v**Example 3**A jet aircraft is travelling at you with a speed of 150 m/s and is emitting a sound of a frequency of 2500 Hz. The speed of sound is 320 m/s at this location. What is the change in the plane’s frequency as it flies past you? f ‘ = f ‘ = f ‘ = Δf ‘ = f ‘ = 2500 Hz 2500 Hz x 0.681 2500 Hz x 1.882 4705 Hz 3000 Hz f 1702 Hz v 320 f ‘ = f ‘ = Doppler Effect v+us 320 +150**Sonic Boom**A special case of the Doppler effect where the object generating the wave is actually moving faster than the wave. This creates a “bow” wave of a super-wave that follows the moving object Doppler Effect Sonic Boom Explanation Video of a Sonic boom in flight.**Do Problems: #49 – 51, 53 – 55 on p. 348 – 349 of**your text book Note: For #55 beat frequency = Δf Doppler Effect**Do Problems from p. 318 - 321**# 38, 51, 52, 54 Doppler Effect The End