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Phys 101 learning object lo7 8 beats

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Physics 101   lo8 (week 10)
Physics 101 lo8 (week 10)
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Phys 101 learning object lo7 8 beats

  1. 1. Physics 101 LO7/8 Vivian Tsang 14153143
  2. 2.  Two waves with slightly different frequencies will combine at some point so that their crests or troughs coincide  When this happens, a maximum sound is heard because the displacement is at its maximum  When the waves go out of phase, the amplitude of the resultant waves decreases  When this happens, a minimum sound is heard because the displacement is at zero  Beats are the periodic variation of sound levels that occur when two waves of slightly different frequencies interfere
  3. 3. D1(0, t)=sin(10pit) D2(0, t)=sin(12pit) D(0, t)=sin(10pit)+sin(12pit)
  4. 4.  The number of times the sound level is at its maximum in one second  Beat Frequency=the difference between the two frequencies fbeat=I f1-f2 I
  5. 5.  The human ear can only differentiate between a beat frequency of 10 beats per second  fbeat=I f1-f2 I < 10  After this level, the two waves go periodically in and out of phase and our ears are not sensitive enough to detect the differences
  6. 6.  Two tuning forks of frequencies 200Hz and 204 Hz are struck so that they simultaneously produce sound waves  What is the beat frequency ?
  7. 7. fbeat=I f1-f2 I  Let f1= 200Hz  Let f2= 204Hz  fbeat=I 200-204 I  fbeat=I -4 I  fbeat= 4Hz
  8. 8.  A cellist is tuning the middle C (262 Hz) string on his cello by listening for beats when this note is played with a tuning fork at the frequency desired. He hears 5 beats per second and notices that when he decreases the tension in the string slightly, the beat frequency degreases. What was the frequency of the out of tune string?
  9. 9.  A) 253Hz  B) 224Hz  C) 267Hz  D) 273Hz  E) 257Hz
  10. 10.  C) 267Hz  Reason:  The beat frequency is found to be 5Hz  This is because the cellist hears 5 beats per second when he tunes his instrument  According to fbeat=I f1-f2 I, the cello must be 5Hz off from the middle C frequency of 262Hz  When he decreases the tension, the beat frequency decreases which means that the instrument is getting more in-tune (less beats heard)
  11. 11.  Therefore, because we know that decreasing string tension also decreases the frequency of the string’s oscillation, we can deduct that the original frequency of the string must be higher by 5 Hz compared to middle C

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