Inductors have duality, right? In an LC circuit, when the capacitor still has charge, it is a passive component, right? It is consuming current, where charge is entering the positive ‘terminal’ of an inductor.
However, when the capacitor charge is depleted, an inductor behaves as a power source.
V = L(di/dt) and V = -L(di/dt)
is the negative one only used when considering Kirchoff’s loop law, and the current entering the inductor from a discharging capacitor? But when calculating the voltage across an inductor, it is the + variant? I am confused as to when to consider + and –
I am really confused.
In: 1
I think you are relying a little too much on the equations trying to figure this out without really thinking about what an inductor does.
An inductor resists change in current. It does this by using its energy stored in its magnetic field to create a voltage trying to restore some of the old current going through it. If the current from A to B across the inductor starts dropping, it will create a positive voltage from A to B to try to restore some of that current. If the current across A to B starts increasing, it will create a negative voltage to resist this increased current. If the current from A to B is negative and dropping (aka increasing in the negative direction), there will be a positive voltage to resist this.
The equation itself shows all of this, V = -L(di/dt) is the one correct equation for inductance. di/dt denotes a change in current, the L denotes the strength of the inductor, and the negative shows that it resists this change, it will always spawn a voltage opposite of what the current is trying to increase or decrease.
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