Magnetic effect of electric current

[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

 

[davenn]

Hi there Karan

welcome to PF

As per my knowledge the magnetic field of Current does not have any poles.

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

Then how a solenoid and a bar magnet's magnetic field be similar?

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

 

[Karan Punjabi]

Yes I know but i want to 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?

 

[Dale]

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

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

 

[Vanadium 50]

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

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

 

[cnh1995]

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

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.

 

[Karan Punjabi]

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.

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

 

[sophiecentaur]

But let me consider a straight current carrying conductor.If current is flowing in upward direction

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.

 

[Karan Punjabi]

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.

Can't i consider a Rectangular circuit?

 

[sophiecentaur]

A rectangular loop is still a loop.

 

[Karan Punjabi]

A rectangular loop is still a loop.

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 ?

 

[Dale]

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

 

[Karan Punjabi]

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

Can i get the reason?

 

[Dale]

You can consider the needle to be a magnetic moment.

https://en.m.wikipedia.org/wiki/Magnetic_moment

So that is the orientation with no torque.

 

[Karan Punjabi]

You can consider the needle to be a magnetic moment.

https://en.m.wikipedia.org/wiki/Magnetic_moment

So that is the orientation with no torque.

Seems to me that I have a limited knowledge till now

 

[davenn]

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

yes, its a circular field :)D

 

[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

 

[Dale]

I would probably start here

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html

 

[Karan Punjabi]

I would probably start here

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html

Ohk i understood everything given in the link

 

[Karan Punjabi]

So how to relate these with poles?

 

[Dale]

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.

 

[Karan Punjabi]

A

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.

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 ?

 

[Dale]

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

 

[Karan Punjabi]

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

ohk got u

 

[sophiecentaur]

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 ?

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).

 

[Karan Punjabi]

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).

The same thing works with the magnet too? If yes then the poles are the places where magnetic needle gets a specific direction ,correct?

 

[sophiecentaur]

The same thing works with the magnet too? If yes then the poles are the places where magnetic needle gets a specific direction ,correct?

A compass will point in a "specific direction" wherever you place it (as long as the field is strong enough to overcome the friction of the compass bearing. You will be familiar with the diagrams in this link, which show the field lines around a magnet (solenoid and bar). The lines never 'end' and their direction is 'specific' everywhere.

 

[Karan Punjabi]

Yeah t

A compass will point in a "specific direction" wherever you place it (as long as the field is strong enough to overcome the friction of the compass bearing. You will be familiar with the diagrams in this link, which show the field lines around a magnet (solenoid and bar). The lines never 'end' and their direction is 'specific' everywhere.

Yeah the lines of solenoid and bar magnet are never ending they are like a loop. And can you tell me that by making a conductor's shape into circular coil like structure and passing current through it how one end is described as north pole and one as south, just want to know that exactly what happens?

 

[sophiecentaur]

Yeah t

Yeah the lines of solenoid and bar magnet are never ending they are like a loop. And can you tell me that by making a conductor's shape into circular coil like structure and passing current through it how one end is described as north pole and one as south, just want to know that exactly what happens?

Just look at the field pattern of a loop of wire (Google it yourself). You will see that the lines through the middle all point the same way. Did you ever hear of the Corkscrew Rule, which tells you the direction of the field around a wire? There are hundreds of pictures on the www which demonstrate all the ideas in this thread. Perhaps some searching and reading could be more useful than just repeating the same questions.

 

[Karan Punjabi]

Just look at the field pattern of a loop of wire (Google it yourself). You will see that the lines through the middle all point the same way. Did you ever hear of the Corkscrew Rule, which tells you the direction of the field around a wire? There are hundreds of pictures on the www which demonstrate all the ideas in this thread. Perhaps some searching and reading could be more useful than just repeating the same questions.

Ohk thanks for this much of knowledge

 

[sophiecentaur]

That 'knowledge' is available in many many places - in pretty well all elementary Physics books.

 

[Karan Punjabi]

That 'knowledge' is available in many many places - in pretty well all elementary Physics books.

Can you suggest some good books on physics

 

[sophiecentaur]

Can you suggest some good books on physics

Almost anything you can get your hands on that you find understandable. Does your school / college / whatever have any such books? As I don't know your present state of learning, I can't be any more specific, I'm afraid.

 

[Karan Punjabi]

Basically, I'm studying in college and one of my classmate has a book named as HC VERMA on physics.My classmate says its an advanced book but first i want to go for basics in physics.

 

[sophiecentaur]

My best suggestion is that you ask a teacher at your college. That will (should) put you in the right direction.