Permanent Magnet vs. Electromagnet: What's the Difference?

[Xidike]

My Question is same as the title of this thread.. and Secondly..
what is the difference between electromagnet and magnet??

 

[Drakkith]

Take a piece of magnetic material, put it in a magnetic field. It should hold its magnetic field once removed.

An electromagnetic uses electric current through a coil to produce its magnetic field. A permanent magnet does not.

 

[sophiecentaur]

Take a piece of magnetic material, put it in a magnetic field. It should hold its magnetic field once removed.

An electromagnetic uses electric current through a coil to produce its magnetic field. A permanent magnet does not.

I think that makes it sound a bit too simple. If you want a 'good' permanent magnet then you need a material that will 'hold it's magnetism' (good 'remnance') once it has been formed. Steel (not stainless) is a good start, although fancy ceramics are better. You then need to use a strong electromagnet (damned great piece of iron 'horseshoe shape' with a small gap between the poles). There are loads of coils of wire wrapped round it and there needs to be loads of current flowing. You turn on the current, having placed your piece of steel in the gap, there's a 'gnurrrr' as the electromagnet is activated. You turn off the current and your piece of steel is then left magnetised.
Alternatively, you can use the 'stroking' method (see all kid's textbooks) which can magnetise a steel screwdriver by stroking it with a strongish permanent magnet. This will magnetise the screwdriver enough to pick up pins and iron filings but not much more.

Railway lines become magnetised weakly by the Earth's field as they are bashed by the trains going over them.

 

[Drakkith]

Yeah, I was on my phone at lunch and couldn't really elaborate. I meant to come back to this thread when I got home.

 

[sophiecentaur]

I thought it was a bit 'terse' for you. ;-)

 

[Drakkith]

I thought it was a bit 'terse' for you. ;-)

Better than being 'Tense'!

 

[phinds]

Better than being 'Tense'!

And WAY better than being past-tense

 

[Khashishi]

An electromagnet is a coil of wire, where a magnetic field appears when electricity is run through the wire. The electromagnet only acts like a magnet as long as there is a current in the wire, so it needs to be connected to some kind of power source.

A permanent magnet doesn't need an external power source. Permanent magnets have a current that doesn't go away. The current comes from alignment of spins of the electrons (and to a much smaller extent, nucleons). In some materials, at sufficiently low temperatures, the spins of the "free" electrons spontaneously align themselves so that they all point the same way. This creates a magnetic domain. If the magnetic domains are large enough, the material is "magnetized" and behaves as a permanent magnet.
You should check out https://en.wikipedia.org/wiki/Ferromagnetism
Obviously, I glossed over a lot of detail. You should study up on quantum mechanics and atomic physics.

 

[Drakkith]

Just to be clear, permanent magnets do not have current flowing through them.

 

[Xidike]

what is mean by magnetic material ? Is iron a magnetic material ?? and what about copper ??

 

[davenn]

yes iron is as are a number of other metals

copper -- no

do a google search on rare Earth elements for magnets

Dave

 

[Khashishi]

Just to be clear, permanent magnets do not have current flowing through them.

The magnetization can be represented as being due to a bound current. Charge doesn't actually flow through the material, but there is a net current along a loop around the edge of the magnetic domain. Maxwell's laws requires there to be a current, though I'm not sure how one could demonstrate that it is indeed a real current.

 

[Xidike]

Can a copper wire act like a magnet when current is passing through it ?

 

[jtbell]

Better than being 'Tense'!

And WAY better than being past-tense

Or too tense:

https://www.physicsforums.com/showthread.php?p=2329281#post2329281

 

[Buckleymanor]

You can make a permanent magnet by heating a rod of iron till it's red hot.
Then you put the hot iron on an anvil with the ends of the rod pointing north and south and bash it along it's length with a hammer.
So I have been told.

 

[Xidike]

Can we make a permanent magnet at our home ?

 

[Xidike]

And how to make an electromagnet ?? which type of current (AC or DC) should be passing through the wire to make it magnetize ? Or it doesn't matter ??

 

[Drakkith]

Well, technically it doesn't matter. However an AC current will alternate the polarity at the frequency of the circuit. So all electromagnets used actually as a magnet to pick up stuff will be DC.

http://en.wikipedia.org/wiki/Electromagnet

 

[Xidike]

How Can I make a permanent magnet at My home ?

 

[davenn]

How Can I make a permanent magnet at My home ?

take a screwdriver or other piece of iron/steel and repeatedly stroke along the length of it with a permanent magnet. The more often done, the more the piece of metal will become magnetised

Dave

 

[sophiecentaur]

Can we make a permanent magnet at our home ?

There is no way that you can do it electrically because you need a large steaming piece of kit to get a good result but, if you already have one of those 'super magnets' (available from many sources) you can easily magnetise a steel object with the 'stroking method' (look it up for how to do it). One good thing to do is to magnetise a steel rod / tool and hang it on a thread or float it on a saucer in water. It will make a pretty convincing compass. You need to keep stroking for quite a while but don't worry, you are unlikely to be de-magnetising your permanent magnet because the energy for magnetising the rod comes from you.

 

[Xidike]

I've tried stroking method and stroked about 50-60 times (is it enough ) at piece of iron but It doesn't become magnetized ,,, why ??

 

[sophiecentaur]

Iron will not work. It had no remnance. Use STEEL like I said.

 

[davenn]

OK
here's a pretty pic of how I usually magnetise a length of steel like a screwdrive blade...

NOTE the circular pattern I use
even as few as 10 passes will have the blade easily magnetised to pick up and hold screws etc

Dave

 

[Buckleymanor]

Iron will not work. It had no remnance. Use STEEL like I said.

(damned great piece of iron 'horseshoe shape' with a small gap between the poles).

Is iron not suitable to be made into a magnet but suitable to become an electro magnet.
What do you mean by remnance.

 

[Drakkith]

Is iron not suitable to be made into a magnet but suitable to become an electro magnet.
What do you mean by remnance.

Remanence or remanent magnetization is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. It is also the measure of that magnetization.

http://en.wikipedia.org/wiki/Remanence

 

[Xidike]

what is bar magnet ??

 

[davenn]

what is bar magnet ??

Bar magnet

ever tried google ? its a wonderful thing :)

Dave

 

[Xidike]

A rectangular shaped magnet is called bar magnet ??

 

[davenn]

yes
any long and roughly rectangular object is often called a bar
eg a bar of chocolate, a musli bar, ...