Power consumption in LCR circuit

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Discussion Overview

The discussion revolves around power consumption in an LCR circuit with a variable frequency AC supply. Participants explore the relationship between frequency, impedance, reactance, and power consumption, particularly at resonance and other frequencies.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that at resonance, the impedance equals resistance, leading to power consumption being purely resistive, and questions if this holds true for other frequencies.
  • Another participant states that reactances do not consume power, as they store and release energy, with power being consumed only by resistive loads. They note that at resonance, the power factor is unity, indicating that all input power is consumed by the resistor.
  • A different viewpoint highlights that reactances can influence the power dissipated by resistive elements, suggesting that LC combinations can affect load matching and power dissipation without consuming power themselves.
  • Another participant mentions that varying frequency impacts impedance, which in turn affects the current through the resistor, indicating that reactances play a role in the power absorbed by the resistor, despite not consuming power directly.

Areas of Agreement / Disagreement

Participants express differing views on the role of reactance in power consumption, with some emphasizing that reactances do not consume power while others argue that they influence the power dissipated by resistive elements. The discussion remains unresolved regarding the extent of reactance's impact on power consumption.

Contextual Notes

Participants reference concepts such as resonance, power factor, and the Maximum Power Theorem, but do not clarify the assumptions or definitions underlying these terms. The discussion does not resolve the mathematical implications of varying frequency on power consumption.

Dexter Neutron
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If we have a variable frequency AC supply in LCR circuit and when the frequency equals natural frequency the impedence is equal to resistance and the power consumption is purely that of resistive load circuit.
Is this true even for other frequencies i.e. do reactance participates in power consumption or not.
 
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Reactances do not consume power. They store the energy and release it back to the source in a cycle. Power is consumed only by the resistive loads. In case of resonance, power factor of the circuit is unity, meaning the reactive power is 0. So, whatever power is input, all of it is consumed in the resistor.
 
It's worth while pointing out that the reactances in a circuit can affect the amount of power dissipated by the resistive elements. The LC combination can match or mismatch the load R (Edit: transform it) and the source, despite not dissipating any power themselves. For instance, the low power dissipated by a high resistance from a low voltage AC supply can be increased as much as you like by LC matching. The only limit is when you hit the Maximum Power Theorem condition, where the source resistance is the same as the transformed load resistance.
 
Last edited:
Worth mentioning that varying the frequency will impact the impedance which varies the current passing through R. Therefore, the reactances play a role in the power absorbed by R, although L & C do not consume power.
 

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