Why Voltage is Lagging the Current in Inductor

Discussion in 'General Electronics Chat' started by amit_telar, Jan 3, 2009.

1. amit_telar Thread Starter New Member

Jan 3, 2009
5
0
Dear All

Why Voltage is Lagging the Current in Inductor? What Factor in Inductor Affects that result in Voltage lagging to Current?

Regards,
Amit

2. silvrstring Active Member

Mar 27, 2008
159
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Amit,

It's the other way around. Voltage lags for capacitors. Current lags for inductors.

The reason is that for a capacitor i = C (dv/dt), and for an inductor v = L (di/dt).

The inductor is initially 'seen' as an open with no current, but the rate of change of current is very high at first. So the initial voltage across the inductor is at its peak when the current starts to get through. As time passes, maximum current is reached and rate of change of current approaches zero. So now the inductor will be like a short with no voltage across it. When the inductor is allowed to 'collapse' its field created by the current, rate of change of current will change quickly again inducing voltage until rate of change of current is zero. It's the opposite of a capacitor.

If you draw this on a graph, you'll see current beginning at the origin. Voltage, however, will already be up because current is changing in the inductor. Therefore, voltage is leading.

3. CanElec Member

Nov 23, 2008
24
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A saying you can use to remember which is which:

ELI ICE

(E)Electromotive force
(L)Inductors
(I)Current

(I)Current
(C)Capacitors
(E)Electromotive Force