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Unformatted text preview: The Physics of Light & Sound Introduction The Doppler effect (or Doppler shift) is the change in frequency of a wave for an observer moving relative to the source of the waves. It is commonly heard when a vehicle sounding a siren approaches, passes and recedes from an observer. The received frequency is increased (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is decreased during the recession.In this experiment you will measure the difference in frequency between a source moving towards and away from you and use the Doppler relationship to determine its velocity. You will also calculate the actual velocity of the source’s motion to compare with your result. Formulae The Doppler relation is given by: Δ λ λ = v c (1) where λ is the wavelength if the source were stationary, Δλ is the difference between the stationary source wavelength and the wavelength observed will moving, v is the speed of the source and c is the wave speed. Wavelength, frequency, and wave speed are related by λ f = c (2) Equipment/Materials: • Fexible hollow tube • computer • PASCO software • meter stick • microphone Summer 2011 1 Lab 09 L AB 09: T HE D OPPLER E FFECT G ENERAL S CIENCE 121 S UMMER 2011 The Doppler Effect Experimental Procedure 1. Prepare the computer for data collection by opening Exp 22 from the intro PhysicsLab folder. The display will include both a graph and an FFT window. The horizontal axis of the graph has time scaled from 0 to 5 s and the vertical axis corresponds to the variation in air pressure; the units are arbitrary. The FFT display has frequency on the horizontal axis scaled from 0 to 2000 Hz.are arbitrary....
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- Spring '08