# Magnetic effect of electric current

1. Oct 10, 2015

### Karan Punjabi

I'm confused that what is the main difference between the magnetic field produced by electric current and the magnetic field produced by a real bar magnet? As per my knowledge the magnetic field of Current does not have any poles. Then how a solenoid and a bar magnet's magnetic field be similar?

I'm in FYJC Science

2. Oct 10, 2015

### davenn

Hi there Karan

welcome to PF

really ? ... did you know ( as far as has been so far discovered) that magnetic monopoles don't exist ?
therefore a N and S pole will exist is all magnetic fields

here's a link to typical solenoids ....

http://www.bing.com/images/search?q=magnetic+field+of+a+solenoid&FORM=HDRSC2

they all seem to have N and S poles to me

cheers
Dave

3. Oct 10, 2015

### Karan Punjabi

Yes I know but i wanna say in a straight current carrying conductor whatever may be the direction of the current the magnetic field are circular non ending have a certain circular direction.ri8? Then hiw the field lines have poles?

4. Oct 10, 2015

### Staff: Mentor

The field around a long straight wire does not have any poles.

5. Oct 10, 2015

Staff Emeritus
Dale's right. And neither does the field in a magnet. Here's a picture from the University of Delaware.

6. Oct 10, 2015

### cnh1995

Here's what I think..A current carrying solenoid is magnetically same as a bar magnet. But the magnetic field of a straight wire is circular around itself. When we say 'current carrying conductor', there must be one more conductor to provide closed path. This conductor will have current in the opposite direction. So practically its a current carrying loop or a one-turn solenoid. So it will look like the picture above in vanadium 50's reply. The circular field of wire is the field around the length of rectangular magnet in the above diagram.

7. Oct 10, 2015

### Karan Punjabi

I got u everyone. But let me consider a straight current carrying conductor.If current is flowing in upward direction and and we take a point anywhere like on the left side of conductor then at that point the magnetic field will be in upward direction then if i keep a magnetic needle there at that point then how and why the magnetic field of electric current will react to that magnetic needle. Basically I'm talking about the thing related to Biot savart law. If I understood this then i will be able to propose my question perfectly to you guys

8. Oct 10, 2015

### sophiecentaur

A straight wire is only an artificial construct. You always need a loop, however big, to get a current flowing in the wire and a loop will exhibit magnetic poles.

9. Oct 10, 2015

### Karan Punjabi

Can't i consider a Rectangular circuit?

10. Oct 10, 2015

### sophiecentaur

A rectangular loop is still a loop.

11. Oct 10, 2015

### Karan Punjabi

Ohk but still i want to know that at a specific point i kept magnetic needle and the loop is very much long then what will happen ?

12. Oct 10, 2015

### Staff: Mentor

The needle will point tangent to a circle around the wire.

13. Oct 10, 2015

### Karan Punjabi

Can i get the reason?

14. Oct 10, 2015

### Staff: Mentor

15. Oct 10, 2015

### Karan Punjabi

16. Oct 10, 2015

### davenn

yes, its a circular field :)

D

17. Oct 11, 2015

### Karan Punjabi

Guys I understood that in a straight conductor if we will select any point then the magnetic needle will be tangential to that field but i want to know that how two poles are formed when current is passed from n turns of circular coil... Plz explain a little bit in detail

18. Oct 11, 2015

### Staff: Mentor

19. Oct 11, 2015

### Karan Punjabi

20. Oct 11, 2015

### Karan Punjabi

So how to relate these with poles?

21. Oct 11, 2015

### Staff: Mentor

Poles are not really that important. They are just a place where the field lines get close together.

If you want to get very technical then poles are the individual terms in a multipole expansion, usually in terms of spherical harmonics. But for magnets it is easier to think of them just as places where the field lines get close.

22. Oct 11, 2015

### Karan Punjabi

A
At this stage i don't think so i don't should go that technical coz i don't have that much of knowledge to co-operate with but my same doubt comes again that if the magnetic needle is pointing in a tangential direction due to magnetic field of current then how in solenoid either north or south pole gets attracted ?

23. Oct 11, 2015

### Staff: Mentor

In each case the needle just aligns in the direction of the field because that is the direction whee the torque is zero.

24. Oct 12, 2015

### Karan Punjabi

ohk got u

25. Oct 12, 2015

### sophiecentaur

If you look at the way a compass needle points when it is alongside a bar magnet, you will notice that it doesn't actually point at the poles. It lays along the field lines, parallel with the magnet. A magnetic pole is not something that can be described in any terms other than where the lines tend to concentrate. It is quite possible to magnetise a piece of steel that has several 'N' and 'S' poles (i.e. stronger regions of field on the surface).