Here's a problem which I'm having trouble trying to resolve:
Consider a simple RC series circuit - a high pass filter. If I observe
the output signal across the resistor, and compare it to the input signal,
then the phase difference is given by tan(phi) = 1/wCR, which varies from
+pi/2 to 0 as frquency increases. I have no problem with that.
Now let's put an inductor in the circuit, between C and R. The text books
tell me that the phase difference is now tan(phi)=(XL-XC)/R. Obviously
the phase angle is zero at resonance, but this formula seems to tell me that
if the reactance of C is bigger than the reactance of L, then the sign of
phi is *negative*, apparently contradicting my previous paragraph.
Please will somebody help me resolve this apparent contradiction. I tried
deducing the phase myself from the ratio of the imaginary and real parts
of Z, and I got tan(phi)=-(XL-XC)/R, which would seem to satisfy my
observations, but I need to be convinced that this is not just wishful
thinking on my part!
Chris
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| Christopher Deacon | (709) 737-7631 |
| Dept of Physics and Physical| cdeacon@kelvin.physics.mun.ca !
| Oceanography | |
| Memorial University of Nfld | http://www.physics.mun.ca/~cdeacon |
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