# Magnetic field lines in a current carrying circular loop

1. May 30, 2012

### 55sparsh

I wanted to ask that do each point of the current-carrying circular loop would create a magnetic field and hence the magnetic field lines? And if yes wouldn't the field lines produced by each point of the loop would intersect each other? I read somewhere that magnetic field lines never intersect, so magnetic field lines in a circular loop is an exception?

Thank You.

2. May 30, 2012

### Simon Bridge

No - no exception needed.

The points in the space inside the loop to not in any way act as sources for the field lines. The line are wholly imaginary and are representative only of the magnetic field that is generated by the current. There are finite lines through the loop... sort-of related to the field strength: when you see lots of lines close together you have a strong magnetic field.

But you've seen the diagrams - have you ever seen a diagram where the field lines cross?

For completeness:
The points of the loop, do not source field lines either - the magnetic field curls around the wire and does not pass through it.

3. May 30, 2012

### 55sparsh

But now i just wanted to ask whether each point on the Wire (through which current is passing) have their own independent magnetic fields? and if yes then the magnetic field lines produced by each point on the wire intersect each other?

Thank You.

4. May 30, 2012

### ZapperZ

Staff Emeritus
5. May 30, 2012

### 55sparsh

Thanx zz..

But sorry man I am just a 10th grade student, and seriously i am unable to understand this biot-savart law properly....any alternate explanations?? i was just asking that if the current is flowing through a circular loop current carrying wire, would there would be a single magnetic field produced by the whole wire or each point (or each line segment as u say in biot-savart law) will produce its own magnetic field (and hence the magnetic field lines)?

Thank You.

6. May 30, 2012

### shreyakmath

There is no sense of taking each point in the loop as a source of the magnetic field lines. You do can calculate the field for a differential line segment i.e a part of the loop using Biot-savart law.
In simple terms, force fields(electric or magnetic) around any conductor are always the field generated by the system of points constituting the conductor. The main reason is because it isnt feasible to calculate current through each point of the loop and thereby magnetic field due to that point when representing total magnetic field around a current carrying conductor.

7. May 30, 2012

### ZapperZ

Staff Emeritus
Next time, indicate the level that you can understand IN THE VERY BEGINNING. If not, you'll simply annoy people who put in effort to present a response, and it is all for nothing!

Zz.

8. May 30, 2012

### 55sparsh

Thanks shreya

Nd i am very very very sorry zz... i really am
I respect my ur efforts put in the answer...
Its all my fault...
I m sry
Didnt want 2 annoy u

9. May 30, 2012

### 55sparsh

Nd shreyakmath

i noe dat calculating magnetic field from each point of conductor is not feasible

but is it true dat in practicality, every point of conductor produces an individual magnetic field??

10. May 30, 2012

### tiny-tim

welcome to pf!

hi 55sparsh! welcome to pf!
yes to both, but …
… it's horribly complicated, and it really wouldn't help to understand the field

11. May 30, 2012

### Simon Bridge

I'll have a bit of a go:

A small bit of a wire that current passes through has it's own B field looping around it - just one loop. The extra lengths of wire give more loops and, since they cannot cross each other, they are forced to line up around the wire loop like you see in the diagrams.

The lines kind-of repel each other.

12. May 30, 2012

### shreyakmath

yes, each point does produce a magnetic field actually, a field is induced at each point due to a current element dl.
But when studying the effects on conductor, the individual fields aren't considered due to the nature of magnetic field to add up.

13. May 31, 2012

### 55sparsh

Thank You tiny-tim, shreyakmath, ZapperZ and simon bridge for those wonderful answers, these really helped me alot, I couldn't these things on the Net and the books I had.

So Simon Bridge, do the fields just add up or kind-of repel each other??

And shreyakmath, do you mean that because the magnetic fields just add up, the patterns becomes like the one shown in most of the diagrams

Last edited: May 31, 2012
14. May 31, 2012

### Simon Bridge

The same applies to each bit of a straight wire carrying a current.
The fields add up, the field lines repel each other. Remember that the lines are just a handy visualization with no physical presence. As a result we usually end up calculating the fields then drawing the lines to illustrate them.

15. May 31, 2012

### 55sparsh

So Simon Bridge do you mean that actually the fields would repel, but their magnitude would add up?

16. May 31, 2012

### Simon Bridge

No - fields add up by the superposition principle. These are vector fields so you add the vectors not the magnitudes.
When you want to draw the field lines, adjacent lines act is if they repel each other.
The lines are not the field - they are a representation of the field.

You have seen diagrams right?

17. May 31, 2012

### 55sparsh

Yups Simon I have seen those...

at every point of a current-carrying circular loop, the concentric circles representing the magnetic field around it would become larger and larger as we move away from the wire. By the time we reach at the centre of the circular loop, the arcs of these big circles would appear as straight lines. Every point on the wire carrying current would give rise to the magnetic field appearing as straight lines at the center of the loop.

Now if the field lines would repel how would they reach to the centre and appear like straight lines?

And in this diagram I think the magnetic fields are depicted of only 2 points...isn't it??

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18. May 31, 2012

### Simon Bridge

It is because they repel - if they didn't you wouldn't get the line bunching up like that.

Diagrams usually show a 2D cross-section of the field-lines because, you know, paper is 2D. The situation in your diagram has a lot of rotational symmetry so it is much the same for any similar slice through the loop.

But remember - these lines are not real - they are just representative - so we don't have to get anal about it. If you think of the lines as the way a compass needle will align at the location, then a compass needle anywhere on the central line will point along that line - which is all it means.

Last edited: May 31, 2012
19. May 31, 2012

### 55sparsh

So you mean because the lines repel they result in forming a straight line shown in the diagrams?

20. May 31, 2012

### Simon Bridge

You are not paying attention - what did I say the lines represent?