Why I*ε Cannot be Used to Calculate Power

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Homework Help Overview

The discussion revolves around the calculation of power in electrical circuits, specifically questioning the validity of using the product of current (I) and electromotive force (ε) in this context. The subject area includes concepts related to LC circuits and energy storage in inductors and capacitors.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the conditions under which power can be calculated in pure LC circuits, questioning the role of resistance in energy absorption and dissipation. There is an inquiry into the differences between energy storage in inductors and capacitors versus energy dissipation in resistors.

Discussion Status

Some participants have confirmed understanding of the concepts discussed, indicating a productive exchange of ideas. However, the discussion remains open with further exploration of the implications of energy storage versus dissipation.

Contextual Notes

Participants are considering the implications of circuit components being purely inductive or capacitive, with an emphasis on the absence of resistance in these scenarios. This raises questions about the assumptions underlying power calculations in such circuits.

hidemi
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Homework Statement
In a series RLC circuit the rms value of the generator emf is ε and the rms value of the current is i. The current lags the emf by Φ, The average power suppplied by the generator is given by:

A. (iε/2) cos Φ
B. iε
C. i^2/Z
D.( i^2)Z
E. (i^2)R

ans: E
Relevant Equations
P = IV = I^2R = V^2/R
Why can't we calculate use I*ε to obtain the power?
 
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If it is a pure LC circuit (R=0) (or pure L or pure C) there will be no energy/power absorbed.
 
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Keith_McClary said:
If it is a pure LC circuit (R=0) (or pure L or pure C) there will be no energy/power absorbed.
I think I got what you mean, but I would like to double check.
Is it because inductor and capacitor both can store energy while resistance only dissipates energy, and thus resistance is the only electric accessory that can generate power?
 
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Keith_McClary said:
@hidemi Right.
Thank you for confirming!
 

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