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Voltage-Current lead/lag

by brendan_foo
Tags: lead or lag, voltagecurrent
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Nov11-04, 07:39 AM
P: 68
Hi there... I know that in an inductor, its voltage will lead the current by 90 degrees and for a capacitor it wil lag the current by 90 degrees. I have seen the mathematical derivation for this too , but I can't get my head around what is actually physically happening here.

Why is the reactance of a capacitor less at greater frequencies? Whats happening with relation to the charges on the plates etc.. please someone help me, what is 'physically going on', as the mathematical derivation simply isn't enough for my curiousity...

Thanks all
Brendan ;)
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Nov11-04, 11:36 AM
P: 123
You can think of it like in an inductor the voltage (pressure) must come first to overcome the inertia of the electrons in the wire; in a capacitor the current must first pile up electorns on the plates for voltage to develop across them.

Reactance in a capacitor is less at higher frequencies because it is the change in current flow that is felt and higher frequencies mean faster change.
Nov15-04, 12:20 AM
P: 183
Quote Quote by brendan_foo
...Why is the reactance of a capacitor less at greater frequencies?...
The dielectric is an insulator, so the outer-shell electrons are bound to their atoms. They can't jump from one atom to another, as is the case with a conductor. So the current that flows in the dialectric is due to the electrons vibrating back and forth. They encounter less oposition if they vibrate over a short distance, than a long one, which is the case of a high frequency compared to a low one.

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