DC Circuits: Why Is Voltage Across Inductor 0 at Steady State?

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Discussion Overview

The discussion revolves around the behavior of an inductor in a DC circuit at steady state, specifically addressing why the voltage across the inductor is zero under these conditions. The scope includes theoretical explanations and applications of Ohm's law and inductor voltage equations.

Discussion Character

  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that at DC steady state, the inductor behaves like a short circuit, leading to a voltage of zero across it.
  • Others reference Ohm's law, suggesting that if resistance is zero (as in a short), then the voltage must also be zero.
  • A participant mentions the relationship V=L(di/dt) and notes that at steady state, the rate of change of current (di/dt) is zero, resulting in zero voltage across the inductor.

Areas of Agreement / Disagreement

Participants generally agree that the voltage across the inductor is zero at steady state, but they present different reasoning and formulations to explain this phenomenon.

Contextual Notes

Some assumptions regarding the ideal behavior of the inductor and the definitions of steady state may not be explicitly stated, which could affect the interpretation of the discussion.

dleccord
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if the inductor is at dc steady state, the inductor would act like a short.

in this case, why would the voltage across the inductor be zero?

thanks in advance.
 
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According to Ohm's law E=IR if R=0 (a short) then E is also 0.
 
dleccord said:
if the inductor is at dc steady state, the inductor would act like a short.

in this case, why would the voltage across the inductor be zero?

thanks in advance.

A perfect electrical short means there is no electrical resistance. If there is no electrical resistance then there can be no voltage across the short. E=IR or Voltage=Amps times Resistance. As you can see as the resistance decreases so does the voltage.
 
wow thanks, i can't believe i didnt look at ohm's law's simplest.

i was looking for V=Ldi/dt, trying to figure that out but confused myself.

thanks ruko.
 
At t=\infty, the current through the inductor is maximum (for "charging" phase) or minimum (for "discharging" phase) and is no longer changing. Therefore, di/dt=0 amps/sec, so the voltage drop across the inductor is V= L(di/dt) = 0 volts.
 

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