Phase Differences in of voltage in RC and LR circuits

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Discussion Overview

The discussion revolves around the phase differences of voltage in RC (resistor-capacitor) and LR (inductor-resistor) circuits, specifically why the voltage across the resistor leads the voltage across the capacitor by 90° in an RC circuit, while in an LR circuit, the voltage across the resistor lags the voltage across the inductor by 90°. The scope includes conceptual understanding and mathematical reasoning related to alternating current (AC) circuits.

Discussion Character

  • Conceptual clarification
  • Mathematical reasoning
  • Exploratory

Main Points Raised

  • One participant asks for an explanation of the phase differences in RC and LR circuits, noting the specific 90° relationships.
  • Another participant suggests deriving equations for purely resistive, inductive, and capacitive circuits to compare phase differences, referencing the sine and cosine functions' 90° phase difference.
  • A participant expresses difficulty with the mathematical explanation and requests a physical interpretation of the phase differences.
  • One participant indicates they understand the basics of AC and reactance but seeks clarity on why one voltage leads or lags the other.
  • Another participant attempts to explain the relationship in physical terms, stating that in a capacitor, voltage is proportional to the integral of current, while in an inductor, voltage is proportional to the derivative of current.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on how to explain the phase differences, with some favoring mathematical derivations and others seeking physical explanations. The discussion remains unresolved regarding the best approach to clarify these concepts.

Contextual Notes

There are limitations in the discussion regarding the reliance on mathematical equations versus physical interpretations, as well as the assumptions made about participants' backgrounds in AC circuit theory.

Nadun
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Hey guys can someone please give me a good explanation on why in an RC circuit the resistor voltage is leading the capacitor voltage by 90°. While in an LC circuit the resistor voltage is lagging the inductor voltage by 90°.
Thanks
 
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You are talking about an AC circuit where the voltage is given by the equation V= V0sinωt. (ω= Angular frequency). Represent the current in similar terms and derive respective equations for a purely resistive, purely inductive and purely capacitive circuits. Then compare the phase difference.

Hint: CosΘ and SinΘ has a phase difference of 90 degrees.
 
hmm do you think you could explain it to me in physical terms, cos mathematically seems really confusing
 
Do you want me to explain you the concept behind alternating circuits?
 
I understand the basics of AC, and the concept of reactance, and what a capacitor does and what an inductor does to AC current i just don't get why one leads the other
 
Hhhhmmm...I am not sure I can leave math out of the question and explain in pure english...

The way I see it, in a capacitor, voltage is directly proportional to charge and charge is the accumulation (integral) of current; so, voltage is proportional to the integral of current.

In an inductor, voltage is produce only when the current changes, i.e., voltage is proportional to the derivative of the current.

Without bringing explicit equations into the mix...does this help?
 

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