p2f10_lec09_beatsand doppler_exam2_review

p2f10_lec09_beatsand doppler_exam2_review - Audio Beats...

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Unformatted text preview: Audio Beats Audio Doppler effect Exam 2 Review Physics 1200 Lecture 09 F2010 Demonstration equipment Doppler spinner Mobile card dual function generator and oscilloscope Audio amp and speakers Falstad ripple tank applet iClicker Question 9.01a Two sound sources are played simultaneously. One of them has a frequency of 440 Hz. The other has a frequency of 441 Hz. Which of the following is closest to your perception of the resulting sound? A) You hear nothing - the difference between the sources is too small to hear anything. B) You hear a steady tone at about 440.5 Hz. C) You hear a tone at 440.5 Hz that varies in intensity at 0.5 Hz. D) You hear a tone at 440.5 Hz that varies in intensity at 1 Hz. E) You hear a tone at 881 Hz. What we perceive: Beats View the signal and hear the sound using a Rensselaer Mobile Card. iClicker Question 9.01b Two sound sources are played simultaneously. One of them has a frequency of 440 Hz. The other has a frequency of 441 Hz. Which of the following is closest to your perception of the resulting sound? A) You hear nothing - the difference between the sources is too small to hear anything. B) You hear a steady tone at about 440.5 Hz. C) You hear a tone at 440.5 Hz that varies in intensity at 0.5 Hz. D) You hear a tone at 440.5 Hz that varies in intensity at 1 Hz. E) You hear a tone at 881 Hz. Beats Previously we considered two interfering waves with the same ϖ . Now consider two different frequencies. When waves of two slightly different frequencies arrive at a point, a detector (ear?) at that point is subjected to two different sinusoidal signals. The superposition of those two signals produces “beats”. Beat frequency – the math ( 29 ( 29 1 2 1 2 2 1 cos( ) cos( ) 1 1 2 cos cos 2 2 m m m s s t s t s t t ϖ ϖ ϖ ϖ ϖ ϖ = + =- × + ( 29 2 cos ' cos m s t t ϖ ω = × ( 29 ( 29 1 2 1 2 1 1 ' 2 2 , ϖ ϖ ϖ ω ϖ ϖ =- = + So you hear both the difference and the average frequency at the same time. What we perceive-2-1 1 2 50 100 150 200 250 Time (sec) amplitude (m) T beat T 1 2 cos ' 1-1 2 ' . We hear a tone at the average frequency whose amplitude varies. The amplitude reaches a maximum whenever is or , so the perceived beat frequency is t ϖ ϖ ϖ ϖ + =- Doppler (frequency) shift A wave front emitted from a point source moves symmetrically away from the source in a spherical pattern. (r=ct) If the source moves, then the center of sequential spheres moves. See Falstad ripple tank demo iClicker question 9.02 A B C Three stationary observers A, B, C are listening to a moving source. Which observer hears the highest pitch? A) A B)B C)C D) They are all the same. iClicker question 9.03 A B C Three observers A, B, C are listening to a moving source. Which observer measures the greatest wave speed ?...
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This note was uploaded on 10/17/2011 for the course PHYS 1010 taught by Professor Schroeder during the Spring '07 term at Rensselaer Polytechnic Institute.

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p2f10_lec09_beatsand doppler_exam2_review - Audio Beats...

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