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## Main Question or Discussion Point

Hi, i was wondering why is it that for an inductor the current lags voltage and for capacitor the current leads voltage? Thank You.

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Hi, i was wondering why is it that for an inductor the current lags voltage and for capacitor the current leads voltage? Thank You.

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I'll add the best way to remember what occurs in each device is our good old pal: ELI the ICE man.

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The capacitor is the counterpart of the inductor. Its stored energy is proportional to the square of the voltage. In a cap, current may change abruptly, whereas voltage must change gradually. Work needs to be done to change its voltage, but not its current. In a real cap, there is always some inductance, so that some work is done changing the current.

Off the top of my head, that is a brief overview. More detail can be added, but that is the basic reason.

mheslep

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Mathematically, you can see lag and lead (phase difference) from:

[tex]

L\frac{di}{dt}= v

[/tex]

[tex]

C\frac{dv}{dt}= i

[/tex]

so that if the current i(t) through an inductor with inductance L is sin(t), then the voltage v(t) across the inductor is cos(t).

Asfor a*physical* why, look to the energy uptake and release by the magnetic field of the conductor and similarly with the electric field in the capacitor.

[tex]

L\frac{di}{dt}= v

[/tex]

[tex]

C\frac{dv}{dt}= i

[/tex]

so that if the current i(t) through an inductor with inductance L is sin(t), then the voltage v(t) across the inductor is cos(t).

Asfor a

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