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E5B08

ELECTRICAL PRINCIPLES · Time constants and phase relationships: RL and RC time constants; phase angle in reactive circuits and components; admittance and susceptance

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What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 300 ohms, R is 100 ohms, and XL is 100 ohms?

  1. A63 degrees with the voltage lagging the current
  2. B63 degrees with the voltage leading the current
  3. C27 degrees with the voltage leading the current
  4. D27 degrees with the voltage lagging the current
Why In a series RLC circuit the reactances subtract: X = XL - XC = 100 - 300 = -200 ohms, so the net reactance is capacitive. The phase angle is arctan(X/R) = arctan(-200/100) = arctan(-2) = -63 degrees. A capacitive circuit makes current lead the voltage, which is the same thing as saying the voltage lags the current.
Watch out The choice with voltage leading by 63 degrees has the right magnitude but the wrong sense; that would be an inductive circuit where XL exceeds XC. The 27 degree answers come from taking arctan(R/X) instead of arctan(X/R).
ELI the ICE man: in ICE (capacitive), I comes before E, so current leads and voltage lags. tan(angle) = (XL-XC)/R.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
← E5B07 All of E5B E5B09 →

The rest of E5B

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  4. E5B04 What is the time constant of a circuit having two 220-microfarad capacitors and two 1-megohm resistors, all i…
  5. E5B05 What is the effect on the magnitude of pure reactance when it is converted to susceptance?
  6. E5B06 What is susceptance?
  7. E5B07 What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 500 …
  8. E5B08 What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 300 …
  9. E5B09 What is the relationship between the AC current through a capacitor and the voltage across a capacitor?
  10. E5B10 What is the relationship between the AC current through an inductor and the voltage across an inductor?
  11. E5B11 What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 25 o…
  12. E5B12 What is admittance?
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