# Direction of Magnetic field

#### electronicsman

##### Full Member level 5
I am trying to understand the basics of magnetic field, if I know this answer i have one more clarification to ask

Based on the magnetic field is my representation of North and South pole correct. The magnetic field originates at North pole and ends at South pole?

#### Akanimo

Hi,

How do you mean originate...and end...? The field direction does not imply movement of the field. It implies the existence of a static field that has the potential to cause influence on a magnetically polarized body in a predefined way. The direction of the field is just an arbitrary reference, just like we have +ve and -ve for electric field.

#### electronicsman

##### Full Member level 5
I come to the actual problem i want to understand

I am representing a stator with 3 winding's 120 degrees, I am trying to simulating rotating magnetic field. Now in a rotating magnetic field the net magnetic field Bs will be rotating, Similarly in the document there is North and South pole also rotating. So, I assume the magnetic field Bs can also be interpreted as North and South Pole. Am i correct? And one particular instant as shown in the diagram the Bs is pointing to right, so i assume the North and South pole are originating at one end and ending at the other end. I am not sure if it is just representation or it is the actual situation. Please correct me.

#### KlausST

##### Super Moderator
Staff member
hi,

unless you want to do some position control, then it makes no difference. the voltage will be positive and negative - in best case - according a sine shape.

But I see a little mistake in your picture.
a, c´, b, a´, c, b´ .. is correct. But the marking on <a> should be a dot and tthe marking at <a´> should be an X .. to get equal 120° aligned sine waveform.

Klaus

#### electronicsman

##### Full Member level 5
hi,

unless you want to do some position control, then it makes no difference. the voltage will be positive and negative - in best case - according a sine shape.
Klaus
But I am doing position control, can you please explain what i have asked.

But I see a little mistake in your picture.
a, c´, b, a´, c, b´ .. is correct. But the marking on <a> should be a dot and tthe marking at <a´> should be an X .. to get equal 120° aligned sine waveform.
Klaus
I have referred another website and the original document the representations are correct only. It is only current at a particular instant, not sure what is wrong. Please help.

#### c_mitra

Based on the magnetic field is my representation of North and South pole correct. The magnetic field originates at North pole and ends at South pole?
Right.

The magnetic field is a vector field.

You place a test unit north pole at a given position position and the direction and magnitude of the force experienced by this test pole defines the magnetic field at that point.

The magnetic lines of forces are continuous; that means they travel from the south pole to the north pole within the magnetic material (this is an important difference from the electric lines of forces).

##### Super Moderator
Staff member
Magnetism arises from electron spin. There's one direction of spin, and there's the opposite direction. The field (or flux) doesn't originate from a particular place.
Nor does an electron spin 'north' and another 'south'.

A north pole is never separate from a south pole.

We call it north and south because a compass points north with the blue end of the needle even though in reality that end is magnetized to be a south pole. I don't know about you but it's become so I have trouble getting my mind around it.

#### electronicsman

##### Full Member level 5

I understand it is very tough for me to put across my questions, but this is what i am expecting, if see the bar magnet there is North and south pole and the field lines start from N and end at S. Similarly in the initial diagrams i wanted to know if they can be represented as N and the S poles based on the Magnetic field. Most of the time I am not sure if the question I ask makes sense or not.

#### c_mitra

Magnetism arises from electron spin.
Is not accurate; magnetism arises due to flow of charge or current. But yes, ferromagnetism, para and dia-magnetism are all intimately connected with the electron spin. Nuclear magnetism is primarily due to nuclear spin.

if see the bar magnet there is North and south pole and the field lines start from N and end at S
The diagram is wrong because it does not show the lines of forces within the magnet. Magnetic lines of forces are closed and continuous. You may please look up any standard book and see the drawings of the lines of forces for a solenoid.

Electric lines of forces always terminate on an equipotential surface: the lines of forces cannot cross the equipotential surface.

#### electronicsman

##### Full Member level 5
But I see a little mistake in your picture.
a, c´, b, a´, c, b´ .. is correct. But the marking on <a> should be a dot and tthe marking at <a´> should be an X .. to get equal 120° aligned sine waveform.
Klaus
Now i understand why you said this as per the below waveform

One of the currents is always in the negative direction and the other two positive to get a 120 Deg waveform. Hence one of them should be "." and other two "x"

#### venn_ng

##### Member level 5
I am trying to understand the basics of magnetic field, if I know this answer i have one more clarification to ask
View attachment 164352

Based on the magnetic field is my representation of North and South pole correct. The magnetic field originates at North pole and ends at South pole?
Magnetic field always has a loop. This comes from maxwell's equation V.B =0. (V is the gradient operator) This equation says that divergence of magnetic field is 0.

This means, there is always a loop. I think in this case, it goes through the south pole and returns back to the north pole again

#### Easy peasy

on a compass, the N part is North seeking ( i.e. actually a South pole ) and the the S part is south seeking, i.e. a North pole