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RC circuit question: In vs. Out phase angle 
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#1
Feb1114, 11:57 AM

P: 28

In an RC circuit, the phase angle between the input and output voltages (not current and voltage) seems to be proportional to the amplitude of the output voltage. That is, as the phase angle between input and output goes to plus or minus 90 degrees, the output voltage goes to 0. Why is that?



#2
Feb1114, 03:31 PM

HW Helper
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#3
Feb1114, 04:46 PM

P: 28

Experimentally. I'm not getting it from equations. If you have a high pass filter, and you run the input voltage to a low frequency, the phase angle will go to about 90 degrees between input and output while the output voltage goes to some small amount. I don't know or really care about the exact relation between the two numerically, but it appeared as though that phase angle difference was somehow related to the change in output voltage. I'm really more interested in what physically is going on that both things happen together.



#4
Feb1114, 05:44 PM

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RC circuit question: In vs. Out phase angle
Think of a resonant system that you excite off of resonance. Like a ball on a spring  if you wiggle the end of the spring at a frequency that is not the natural resonant frequency of the ball+spring system, then the ball will often move with a phase shift compared to how you are wiggling the spring. Anyway, here is a typical RC lowpass plot like the behavior you are describing: https://www.library.cmu.edu/ctms/ctm...req/bode1a.gif 


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