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G5A05

ELECTRICAL PRINCIPLES · - Reactance; inductance; capacitance; impedance; impedance transformation; resonance

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How does an inductor react to AC?

  1. AAs the frequency of the applied AC increases, the reactance decreases
  2. BAs the amplitude of the applied AC increases, the reactance increases
  3. CAs the amplitude of the applied AC increases, the reactance decreases
  4. DAs the frequency of the applied AC increases, the reactance increases
Why Inductive reactance is XL = 2πfL, so reactance is directly proportional to frequency: double the frequency and you double the opposition. Physically, a faster-changing current produces a larger back-EMF in the coil, which opposes the current more strongly. Reactance depends only on frequency and inductance, not on how large the voltage or current happens to be.
Watch out The choice saying reactance falls as frequency rises describes a capacitor, where XC = 1/(2πfC); the amplitude-based choices are wrong because reactance is independent of signal level in a linear component.
XL = 2πfL: inductors go UP with frequency, capacitors go DOWN. Amplitude never enters the formula.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of G5A

  1. G5A01 What happens when inductive and capacitive reactance are equal in a series LC circuit?
  2. G5A02 What is reactance?
  3. G5A03 Which of the following is opposition to the flow of alternating current in an inductor?
  4. G5A04 Which of the following is opposition to the flow of alternating current in a capacitor?
  5. G5A05 How does an inductor react to AC?
  6. G5A06 How does a capacitor react to AC?
  7. G5A07 What is the term for the inverse of impedance?
  8. G5A08 What is impedance?
  9. G5A09 What unit is used to measure reactance?
  10. G5A10 Which of the following devices can be used for impedance matching at radio frequencies?
  11. G5A11 What letter is used to represent reactance?
  12. G5A12 What occurs in an LC circuit at resonance?
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