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E5B10

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 an inductor and the voltage across an inductor?

  1. AVoltage leads current by 90 degrees
  2. BCurrent leads voltage by 90 degrees
  3. CVoltage and current are 180 degrees out of phase
  4. DVoltage and current are in phase
Why In an inductor the voltage is proportional to the rate of change of current, V = L(di/dt). The current must start changing before any voltage appears in response, so the voltage waveform reaches its peak a quarter cycle ahead of the current peak. That quarter cycle is 90 degrees, so voltage leads current by 90 degrees in a pure inductance.
Watch out The choice saying current leads voltage by 90 degrees describes a capacitor, where the current must flow first to build up the charge that creates the voltage.
ELI the ICE man: in L, E (voltage) leads I; in C, I leads E.
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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