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AAMC qpack passage 3 q.16
Sukham_5277
#1 Posted : Monday, July 27, 2020 5:41:08 PM
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Hi,
Is the logic to solve this question: when speed of the wave is closer to the speed of source there is a greater doppler effect (change in frequency)

Thanks.
INSTR_Radhika_42
#2 Posted : Tuesday, August 04, 2020 2:03:52 PM
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Hi Sukham,

Would you be able to write out or paste a screenshot of the question here? I'll be able to answer the question better this way.

Thanks!
Sukham_5277
#3 Posted : Tuesday, August 04, 2020 3:02:59 PM
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The question is:
Why are the percentages of the change in frequency and wavelength much greater when sound waves are used instead of radio waves in these experiments?

Sound waves travel more slowly.
Sound waves have a much higher frequency.
Sound waves have a much shorter wavelength.
Interference in the atmosphere affects sound waves much more.
INSTR_Radhika_42
#4 Posted : Friday, August 07, 2020 6:18:18 PM
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Hi Sukham,


Thank you for getting back with the question.

Ok so let's recap some knowledge here:
- Radio waves are part of the EM spectrum and therefore, they travel at the speed of light (as all types of waves in the EM spectrum) *Tip: you should know the order of the entire EM spectrum!*
- Sound waves are not part of the EM spectrum and travel SIGNIFICANTLY slower than EM waves
- Therefore, the velocity of radio waves is much greater than the velocity of sound waves.

Now, let's use POE:
- Eliminate B and C; frequency is inversely proportional to wavelength since v = f(lambda) and you can't have two correct answers!
- Recall the Doppler Equation: (change in f)/(initial f) = (velocity of wave in that medium)/(speed of light) --> here's a link: http://astronomyonline.o...cience/DopplerShift.asp
- Essentially, what the equation says is that the change in frequency is inversely proprtional to the speed of the wave in that medium. The velocity of sound is much smaller than that of EMR, so for the same relative velocity the frequency and wavelength shifts are much greater for sound than for radio waves.

Hope this helps! Let me know if you have follow up questions :)
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