AC inductor circuits

Thread Starter


Joined Feb 29, 2012
I'm a little confused about how AC inductance circuits work. It's a great article, but I have a question.

If the only component in the circuit above is the inductor, then it has to drop all of the voltage provided by the AC source, right? So, if the voltage it drops is an indirect result due to the change in current, well then how could it drop a voltage that isn't whatever the source is applying?

I was wondering if the voltage of the conductor forced the current to change the current in a way that would create this:

Anyway, any assistance would be appreciated.


Joined Mar 14, 2008
But the inductor does drop whatever voltage the source is supplying. Why do you think it doesn't?

Think about how an inductor responds to a voltage. Any voltage across an inductor will cause the inductor current to keep increasing according to di = (V*dt)/L. Thus as long as the AC voltage across the inductor is positive, the current will keep increasing in a positive direction until the voltage reaches 0V. At that point the inductor current is at its positive peak value.

Now the voltage starts to go negative. This now starts slowing the inductor current until eventually it becomes zero (at the negative voltage peak) and then starts to go negative. Again the current will keep increasing (now in a negative direction) until the voltage is back to 0V at which point the inductor current is now at its negative peak value.

From this you can see how the inductive current lags the inductor voltage by 90 degrees.