Lesson 18-Timed MCAT Practice Passage on the Doppler Effect

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wh816
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Joined: Sun Nov 04, 2018 10:40 am

Lesson 18-Timed MCAT Practice Passage on the Doppler Effect

Post by wh816 » Tue Feb 12, 2019 10:31 am

I am having trouble understanding how we were able to obtain the information about whether the vehicle is approaching or is moving away and the change in frequency indicating return frequency is more or less than the emitted frequency from the graph.

Thanks
NS_Tutor_Will
Posts: 529
Joined: Fri May 25, 2018 9:15 am

Re: Lesson 18-Timed MCAT Practice Passage on the Doppler Effect

Post by NS_Tutor_Will » Wed Feb 13, 2019 8:08 am

Thanks for the question!

The basic concept here is that the frequency change will allow us to determine the direction (relative to us) that the car is moving. If the frequency change is negative, that indicates that the vehicle (or object of interest) is moving away from us. If the frequency change is positive, that indicates that the vehicle is moving toward us.

On the graph itself, a positive velocity indicates that the car is moving away from us (and as a result the frequency changes are negative). A negative velocity indicates that the car is moving toward us (which results in a positive frequency change).

While this may be noted specifically on a graph, we can also determine which direction is which based on the frequency shifts.

I hope this helps!
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