# Natural Response of an RL circuit

#### jstrike21

Joined Sep 24, 2009
104
On the first problem in the attached pdf, wouldn't Vo(0-) and Vo(0+) be zero due to the inductor acting as a short?

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#### ELECTRONERD

Joined May 26, 2009
1,147
On the first problem in the attached pdf, wouldn't Vo(0-) and Vo(0+) be zero due to the inductor acting as a short?
In terms of resistance, yes, I would say that you're correct. However, inductors do have a negligible amount of resistance that you can ignore, but that certainly doesn't change the inductance. It's still there.

#### Thav

Joined Oct 13, 2009
82
You can only say an inductor acts as a short to DC current. At t=0 there is a transient event in which case the inductor is most decidedly not a short.

The current in an inductor can not change instantaneously. So at t=0+ the current inductor must be the same as it was at t=0-. Where does that current have to flow to complete the circuit? What can you then tell about the voltage across the inductor?

#### ELECTRONERD

Joined May 26, 2009
1,147
You can only say an inductor acts as a short to DC current. At t=0 there is a transient event in which case the inductor is most decidedly not a short.

The current in an inductor can not change instantaneously. So at t=0+ the current inductor must be the same as it was at t=0-. Where does that current have to flow to complete the circuit? What can you then tell about the voltage across the inductor?
That makes perfect sense.