# Does a wire in a closed circuit induce a voltage on itself?

1. Apr 6, 2014

### rail2k

According to Faraday's Law a changing magnetic field induces an electric field, an example of this is if you have a wire close enough to another wire with current flowing through it the first wire will also have current run through it because of the induced electric field by the second wire.

As current runs through a wire in a closed circuit a magnetic field is created around the wire, so doesn't that mean that that same magnetic field will induce an electric field which will create more current in the wire? If it does, then is the new current opposing the original current or adding to it?

2. Apr 6, 2014

### nasu

Only when the magnetic field is changing in time (increasing or decreasing).
It may oppose or add. See "inductance" and "Lenz's law".

3. Apr 7, 2014

### rail2k

But in the real world when current runs through a closed circuit doesn't the magnetic field constantly change due to a never steady current, just by extremely small amounts?

And in a perfect circuit, if the circuit is initially open but then you close it won't the magnetic field increase as current first travels through the circuit (extremely fast of course)?

If either of those are right, wouldn't the changing magnetic field induce a current to oppose or add to the original current?

EDIT: If you were using an AC power source, wouldn't the current and the magnetic field constantly be oscillating? So then this would constantly induce current, right?

Last edited: Apr 7, 2014
4. Apr 7, 2014

### nasu

In a DC circuit you will have this effect when you turn ON or OFF the power.
In an AC circuit you will have this induced emf whose effect is described by the "inductive reactance". Look up these terms for more information.