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Physics 111.6 Section 01 Lecture 39

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Physics 111.6 Section 01 Lecture 39

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    1. Physics 111.6 Section 01 Lecture 39 The Doppler Effect Applications of sound Linear Superposition of waves

    2. The Doppler Effect The change in frequency (pitch) detected by an observer because the sound source and the observer have different velocities with respect to the medium of sound propagation

    3. Doppler effect movies http://www.wfu.edu/Academic-departments/Physics/demolabs/demos/3/3b/3B40xx.html

    4. Moving Source, Stationary Observer What causes the note heard by a stationary observer from a moving source to vary in pitch? High pitch when approaching (high frequency, short wavelength) Low pitch when receding (low frequency, long wavelength)

    7. A Doppler Effect animation http://www.sciencejoywagon.com/physicszone/lesson/otherpub/wfendt/dopplerengl.htm

    8. Moving observer, stationary source Figure 16.30

    9. Now if the source (the truck) moves forward with speed vs

    14. For the source moving away from the stationary observer The analysis is the same except that the basic relationship between ? and ? is now

    16. Example 10 Train approaching a crossing at 44.7 m/s Sounds a warning horn at 415 Hz Speed of sound is 343 m/s What are the frequencies and wavelengths an observer standing at the crossing hears as the train approaches and recedes?

    19. Moving observer, stationary source The moving observer getting closer to the source encounters an extra number of condensations

    23. Difference in the two cases Source moves, observer stationary The wavelength ? changes, leading to a change in frequency Observer moves, source stationary Observer intercepts a different number of wave condensations per second giving rise to a different frequency The wavelength does not change in this case

    24. General case observer and source moving

    26. Police Radar

    27. Doppler flow meter For determining the blood flow rate in blood vessels near to the skin

    28. Ultrasonic imaging Most often used for prenatal monitoring

    29. Ultrasound in surgery Cavitron ultrasonic surgical aspirator Brain surgery Liver disease Ovarian cancers/cysts

    31. Chapter 17 So far we have considered a single wave occupying a space Suppose we have two waves occupying the same space at the same time What does the waveform look like? How do we treat it mathematically?

    32. Linear Superposition When two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves

    33. Linear superposition Applies to all types of waves Electromagnetic radiation Sound Water waves

    34. Interference Interference effects come about from the addition of two waves with the same frequency It may be either Constructive interference or Destructive interference

    35. Constructive interference If the waves which are being added together have the peaks and troughs aligned they are said to be in Phase Waves which are in phase show constructive interference

    36. Destructive interference When the two waves being added together have the peaks on one wave exactly aligned with the troughs on the other, they are said to be Out of Phase. The two waves show Destructive interference and the net amplitude is zero

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