Series resonance condition — at series resonance, are the inductive and capacitive reactances never equal?

Difficulty: Easy

Correct Answer: False

Explanation:


Introduction / Context:
Resonance in a series RLC circuit is defined by the balance between inductive and capacitive reactances. This balance governs impedance magnitude and phase, and it sets the peak current condition for a given source voltage.


Given Data / Assumptions:

  • Series RLC under sinusoidal steady state.
  • XL = omega * L, XC = 1 / (omega * C).
  • Resonant frequency denoted as omega0.


Concept / Approach:

By definition of series resonance, XL equals XC in magnitude at omega0. The imaginary parts cancel, leaving net impedance Z = R (minimum magnitude). This is the basis for current maximization and purely resistive phase at resonance.


Step-by-Step Solution:

Set condition for resonance: XL = XC.This gives omega0 * L = 1 / (omega0 * C).Solve for frequency: omega0 = 1 / sqrt(L * C).At omega0, Z = R + j(XL − XC) = R, confirming equality and cancellation of reactances.


Verification / Alternative check:

Measured current peaks at resonance and the phase angle between source voltage and current is zero, both confirming that reactive terms are equal and opposite.


Why Other Options Are Wrong:

  • Claims that equality never occurs contradict the definition of series resonance.
  • Parallel resonance is a different topology; the equality condition discussed here is for series resonance.
  • Non-ideal losses do not alter the equality condition; they only broaden the resonance and reduce current magnitude.


Common Pitfalls:

Confusing equality of reactances with equality of impedances. The magnitudes of reactances are equal at resonance; the net impedance is resistive, not zero.


Final Answer:

False

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