Question

What is the response of inductor to DC?

Answer 1

When a direct current (DC) is applied to an inductor, its response can be understood in terms of how the inductor reacts to changes in current:

1. At the Instant DC is Applied:
   

   - Initially, when the DC is first applied, the inductor resists any sudden change in current because of its property called inductive reactance. This means, at the moment the DC voltage is applied, the current through the inductor will start from zero and gradually increase.
   - This initial opposition to the current change is caused by the self-induced voltage (also called back EMF), which is the voltage the inductor generates in the opposite direction to oppose the change in current.

1. After a Long Time (Steady State):
   

   - Once the current has increased and the circuit reaches a steady state, the inductor behaves like a short circuit. In other words, the inductor has zero resistance to DC in steady state. The back EMF disappears because the current is no longer changing. At this point, the inductor just allows the DC current to pass through it with no resistance.

In summary:

1. During the transient period (when DC is first applied), the inductor opposes the change in current.
   

1. After a long time (in steady state), the inductor acts like a simple wire, and there is no opposition to the DC current.
   

So, for DC, the inductor initially resists changes in current, but eventually, it offers no resistance once the current becomes constant.