Understanding Inductor Behavior in a Changing RL Circuit

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Discussion Overview

The discussion revolves around the behavior of an inductor in an RL circuit when the resistance is decreased linearly over time. Participants explore how this change in resistance affects the current and the voltage across the inductor, questioning the relationship between these variables and the nature of the inductor's opposition to changes in current.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that decreasing the resistor value linearly will cause the current to increase linearly, raising questions about how the voltage across the inductor interacts with this change.
  • Another participant challenges the assumption that the current will rise linearly, noting that the inductor will resist changes in current, leading to a delayed response.
  • A different participant proposes that the rate of change in resistance relative to the time constant of the RL circuit may influence the current's behavior.
  • There is a discussion about whether the inductor can stop the current from changing, with some clarifying that it only limits the rate of change.
  • One participant mentions that when resistance is sharply changed, the current will asymptotically approach a final value, indicating a time-dependent response.

Areas of Agreement / Disagreement

Participants express differing views on how the current behaves in response to changes in resistance, with no consensus reached on whether the current can increase linearly or how the inductor's opposition affects this process.

Contextual Notes

Participants highlight the importance of the time constant of the RL circuit and the speed of resistance change, indicating that these factors may not have been fully explored or defined in the discussion.

Slava
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Imagine simple RL circuit connected to a battery source. Let's assume that we are decreasing the resistor value linearly in a constant steady rate. This will make the current being increased linearly. Thus the current will be increasing in an inductor and it will cause a voltage to build up across the inductor which will oppose a further change in current. But will this voltage across the inductor decrease the current in a circuit? Why the current will still be inreasing in the same constant steady rate while the resulting voltage in a circuit has been changed.

Why the voltage which builds up doesn't change the current? Or may be it actually changes the current which changes the voltage again and so on and we don't see these fluctuations?
 
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By what means do you linearly increase that current? There lies your answer.
 
By let's say some electronic circuit or let's assume that I can turn the knob of the resistor with a linear speed. Still don't get the answer :)
 
Sorry, I actually misread your initial post.

What makes you think the current will rise linearly alongside the lowering of the resistor? As you correctly point out, the coil will resist the change in current through a voltage at its terminals. So, the current will have a delayed response to the change in the resistor.
 
Could you please clarify on this please. What do you mean by saying the current will have a delayed response? I see that I am missing something
 
Interesting question. I have never worked this kind of problem before. I would have to run the numbers to know, but I suspect it would depend on how quickly you changed the resistance compared to the time constant of the RL circuit.
 
By saying that the inductor opposes changes in current. Does it actually stop current from changing?
 
Slava said:
By saying that the inductor opposes changes in current. Does it actually stop current from changing?

No. It merely reduces how fast the current can change. With 0 inductance the current could change at any rate. But a real circuit always has non-zero inductance and there is a limit to how fast the current can change.
 
It's simplest to explain with when you sharply change the resistance. The current will asymptotically approach the final value as dictated by the resistor. But it will take some time for it to reach that value.
 

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