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Inductor maze

  1. Apr 20, 2015 #1
    Imagine simple RL circuit connected to a battery source. Lets 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 dont see these fluctuations?
  2. jcsd
  3. Apr 20, 2015 #2
    By what means do you linearly increase that current? There lies your answer.
  4. Apr 20, 2015 #3
    By lets say some electronic circuit or lets assume that I can turn the knob of the resistor with a linear speed. Still dont get the answer :)
  5. Apr 20, 2015 #4
    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.
  6. Apr 20, 2015 #5
    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
  7. Apr 20, 2015 #6


    Staff: Mentor

    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.
  8. Apr 21, 2015 #7
    By saying that the inductor opposes changes in current. Does it actually stop current from changing?
  9. Apr 21, 2015 #8


    User Avatar

    Staff: Mentor

    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.
  10. Apr 21, 2015 #9
    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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