Series resonance condition — at series resonance, are the inductive and capacitive reactances never equal?
-
ATrue
-
BFalse
-
CTrue only for very low Q
-
DTrue only in parallel resonance
-
EFalse only for ideal components
Answer
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