# Is the magnetic induction line closed

1. Oct 30, 2008

### jomoonrain

It is said that every magnetic induction line is closed.but recently I happended to find one which isn't.
Consider the magnetic field generated by a ring form circuit, the magnetic induction line which I have found is not closed is the one that go through the center of the circuit,which is normal to the circuit plane.

Am I right? If not, then how to explain it?

2. Oct 31, 2008

### CompuChip

If you want to see it that way, it is closed in infinity (something like this with a going to infinity-- never mind the i in there).

What is meant by "magnetic field lines are closed" is that no magnetic field lines can start or end anywhere in space or on a material. Therefore, if they are finite, they have to be closed loops. If they extend to infinity on both sides, they automatically do not begin or terminate anywhere.

Another example would be the field lines along the axis of an ordinary bar magnet (image).

3. Oct 31, 2008

### jomoonrain

thank you very much.i've got it.