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E5B09

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 relationship between the AC current through a capacitor and the voltage across a capacitor?

  1. AVoltage and current are in phase
  2. BVoltage and current are 180 degrees out of phase
  3. CVoltage leads current by 90 degrees
  4. DCurrent leads voltage by 90 degrees
Why A capacitor's current depends on the rate of change of voltage: i = C(dv/dt). Current is therefore largest when the voltage is changing fastest (as it crosses zero) and zero when the voltage is at its peak, which puts the current one quarter cycle, or 90 degrees, ahead of the voltage. This is the opposite of an inductor, where the voltage leads the current by 90 degrees.
Watch out The choice saying voltage leads current by 90 degrees describes an inductor, not a capacitor; in phase would describe a pure resistance.
ELI the ICE man: in a Capacitor (C), I comes before E, so current leads voltage.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E5B

  1. E5B01 What is the term for the time required for the capacitor in an RC circuit to be charged to 63.2% of the appli…
  2. E5B02 What letter is commonly used to represent susceptance?
  3. E5B03 How is impedance in polar form converted to an equivalent admittance?
  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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