Question about Permanent Magnets and ElectroMagnets

[adlep]

Pardon My Ignorance,

Suppose that there is a medium sized Neodymium Magnet with a pulling power of 50lb
We also have an access to a small electro magnet with a max pulling power of 1lb

When the current is applied to the electromagnet it gets attracted to the Neodymium Magnet
and it sticks to it

My question is this?
How much power I will have to apply to break these two apart assuming that we can not shutdown the Electro Magnet (the current flows through it)?

Is it going to be only 1lb ( the pulling power of the electromagnet), or it is going to be 50lb (the pulling power of the Neodymium Magnet)?

 

[silverpig]

51 lb?

 

[adlep]

Really?

OK
Provided that you are correct, this is great.
Now what will happen if you will reverse the current of the electromagnet?

The magnetic poles in the electro magnet should reverse. So now you have 51lb of a repulsive force?

 

[BrownTown]

no, then you would have 49 pounds...

EDIT: for calrification that measn there are 49 pounds of attracctive force, the permenant magnet at 50 pound and the repulsive force of 1 pound from the electromagnet. At least that what makes sense to me.

 

[adlep]

Originally posted by: BrownTown
no, then you would have 49 pounds...

EDIT: for calrification that measn there are 49 pounds of attractive force, the permanent magnet at 50 pound and the repulsive force of 1 pound from the electromagnet. At least that what makes sense to me.

OK so if I understand your point correctly then:
You will need to apply 49 pounds of force to detach the electromagnet from the permanent magnet, even though the poles in the electromagnet changed?

Suppose that was the original configuration:

Original case:
+electromagnet- +permanent magnet- (both magnets are stuck together, you need 51lb of force to break them apart)

Modified case (the magnetic poles are reversed in the electromagnet):

-electromagnet+ +permanent magnet- (both magnets are stuck together, you need 49lb of force to break them apart)?

 

[BrownTown]

Well I think the problem with that assumption would be that the electromagnet in fact will not change polarity because there will be a much stronger force attempting to align the magnetic domains with those of the permenant magnet than there will be from the electric current attempting to align them the opposite way. Having said that, and despite the fact that I am an electrical engineer and have taken electromagnetics etc I still have very little confidence in the accuracy of my statements they are simply what intuitively FEELS right to me, if you asked me to try to prove it I owuld be hard pressed to do so.

EDIT: see the problem I have is that if it were another way then you would have that suddeny discontinuity at 0 amps where the force suddenly goes from 50 pouds attractive to 50 pounds repulsive. I guess it would also work if the two forces were multiplied since then there would be a transition in sign, but as a continuous function through 0 ot as a discontinuous function.

 

[Fallen Kell]

Originally posted by: BrownTown
no, then you would have 49 pounds...

EDIT: for calrification that measn there are 49 pounds of attracctive force, the permenant magnet at 50 pound and the repulsive force of 1 pound from the electromagnet. At least that what makes sense to me.

You have that all wrong. If this is a force 50lb magnet which a 1lb force electromagnet connects to from applying a current through the electromagnet; then you switch the polarity of the electromagnet you will have a 51lb repelling force between the two magnets. However, in reality, the electromagnet will probably just flip around as there will be enough force to attract the other pole of the electromagnet assuming the magnets are not in some kind of track/rail system where they can not twist around. This also assumes that the electromagnet is given a strong enough current to change its polarity...

 

[DyslexicHobo]

I have absolutely NO experience with electromagnets, but I'm assuming they work similarly to natural magnets. If you were to have one + magnet capable of holding 50 lbs of ferrous weight, and another + magnet capable holding 1lb, then it seems to me as though you'd need 51 lbs of force to bring them together. The natural magnet isn't going to attract the other if they both have the same polarity.

 

[DrPizza]

Originally posted by: Fallen Kell

Originally posted by: BrownTown
no, then you would have 49 pounds...

EDIT: for calrification that measn there are 49 pounds of attracctive force, the permenant magnet at 50 pound and the repulsive force of 1 pound from the electromagnet. At least that what makes sense to me.

You have that all wrong. If this is a force 50lb magnet which a 1lb force electromagnet connects to from applying a current through the electromagnet; then you switch the polarity of the electromagnet you will have a 51lb repelling force between the two magnets. However, in reality, the electromagnet will probably just flip around as there will be enough force to attract the other pole of the electromagnet assuming the magnets are not in some kind of track/rail system where they can not twist around. This also assumes that the electromagnet is given a strong enough current to change its polarity...

I've got a bunch of powerful neodymium magnets, and a bunch of cheap iron bar magnets. I can assure you that those neodymium magnets do not care which side of the bar magnet they're attracted to. i.e. there is no repulsive force, regardless of their orientation.

 

[adlep]

Originally posted by: DrPizza

Originally posted by: Fallen Kell

Originally posted by: BrownTown
no, then you would have 49 pounds...

EDIT: for calrification that measn there are 49 pounds of attracctive force, the permenant magnet at 50 pound and the repulsive force of 1 pound from the electromagnet. At least that what makes sense to me.

You have that all wrong. If this is a force 50lb magnet which a 1lb force electromagnet connects to from applying a current through the electromagnet; then you switch the polarity of the electromagnet you will have a 51lb repelling force between the two magnets. However, in reality, the electromagnet will probably just flip around as there will be enough force to attract the other pole of the electromagnet assuming the magnets are not in some kind of track/rail system where they can not twist around. This also assumes that the electromagnet is given a strong enough current to change its polarity...

I've got a bunch of powerful neodymium magnets, and a bunch of cheap iron bar magnets. I can assure you that those neodymium magnets do not care which side of the bar magnet they're attracted to. i.e. there is no repulsive force, regardless of their orientation.

Every Permanent Magnet has to have two sides, so you must be living in a black hole

 

[jagec]

Originally posted by: adlep

Originally posted by: DrPizza
I've got a bunch of powerful neodymium magnets, and a bunch of cheap iron bar magnets. I can assure you that those neodymium magnets do not care which side of the bar magnet they're attracted to. i.e. there is no repulsive force, regardless of their orientation.

Every Permanent Magnet has to have two sides, so you must be living in a black hole

Or the iron magnets are weak enough that they just act like plain old iron--in other words, the neodynium magnets are changing the polarity of the bar when they stick to it.

 

[DrPizza]

Originally posted by: adlep
Every Permanent Magnet has to have two sides, so you must be living in a black hole

What the heck are you trying to say? If you didn't understand my post, allow me to clarify: Neodymium magnet has a N pole (or North seeking pole, if you wish), and a S pole. One end of the iron bar magnet is N, the other end is S. The Neodymium magnet's N pole is NOT repelled by the iron bar magnet's N pole. Instead, it's strong enough to reorient the domains in the bar magnet. The N pole of the neodymium magent is actually attracted to the N pole of the bar magnet (which ultimately becomes a S pole)

And, the neodymium's south pole is attracted to both the north pole of the bar magnet (of course) AND the south pole of the bar magnet. (And, the neodymium's N pole is also, of course, attracted to the bar magnet's south pole.)

 

[Fallen Kell]

Originally posted by: DrPizza

Originally posted by: adlep
Every Permanent Magnet has to have two sides, so you must be living in a black hole

What the heck are you trying to say? If you didn't understand my post, allow me to clarify: Neodymium magnet has a N pole (or North seeking pole, if you wish), and a S pole. One end of the iron bar magnet is N, the other end is S. The Neodymium magnet's N pole is NOT repelled by the iron bar magnet's N pole. Instead, it's strong enough to reorient the domains in the bar magnet. The N pole of the neodymium magent is actually attracted to the N pole of the bar magnet (which ultimately becomes a S pole)

And, the neodymium's south pole is attracted to both the north pole of the bar magnet (of course) AND the south pole of the bar magnet. (And, the neodymium's N pole is also, of course, attracted to the bar magnet's south pole.)

Ahhh, but you see, then your iron magnet isn't really a true magnet, it is simply a piece of iron that has had its magnetic field aligned (a temporary magnet), much like if you connect a paper clip to a magnet for a few days, that paper clip will then still exhibit a magnetic field even after disconnecting the magnet from the clip. It will probably last a few minutes/hours as well.

 

[Born2bwire]

Originally posted by: Fallen Kell

Originally posted by: DrPizza

Originally posted by: adlep
Every Permanent Magnet has to have two sides, so you must be living in a black hole

What the heck are you trying to say? If you didn't understand my post, allow me to clarify: Neodymium magnet has a N pole (or North seeking pole, if you wish), and a S pole. One end of the iron bar magnet is N, the other end is S. The Neodymium magnet's N pole is NOT repelled by the iron bar magnet's N pole. Instead, it's strong enough to reorient the domains in the bar magnet. The N pole of the neodymium magent is actually attracted to the N pole of the bar magnet (which ultimately becomes a S pole)

And, the neodymium's south pole is attracted to both the north pole of the bar magnet (of course) AND the south pole of the bar magnet. (And, the neodymium's N pole is also, of course, attracted to the bar magnet's south pole.)

Ahhh, but you see, then your iron magnet isn't really a true magnet, it is simply a piece of iron that has had its magnetic field aligned (a temporary magnet), much like if you connect a paper clip to a magnet for a few days, that paper clip will then still exhibit a magnetic field even after disconnecting the magnet from the clip. It will probably last a few minutes/hours as well.

Well all iron magnets are what you would say are "temporary." Left on their own, a ferromagnet will retain it's magnetic properties for a good while but they are susceptible to realignment of their domains by strong magnetic fields (which are how they are often made in the first place), annealing, or even by physical shock.

 

[silverpig]

Originally posted by: Born2bwire

Originally posted by: Fallen Kell

Originally posted by: DrPizza

Originally posted by: adlep
Every Permanent Magnet has to have two sides, so you must be living in a black hole

What the heck are you trying to say? If you didn't understand my post, allow me to clarify: Neodymium magnet has a N pole (or North seeking pole, if you wish), and a S pole. One end of the iron bar magnet is N, the other end is S. The Neodymium magnet's N pole is NOT repelled by the iron bar magnet's N pole. Instead, it's strong enough to reorient the domains in the bar magnet. The N pole of the neodymium magent is actually attracted to the N pole of the bar magnet (which ultimately becomes a S pole)

And, the neodymium's south pole is attracted to both the north pole of the bar magnet (of course) AND the south pole of the bar magnet. (And, the neodymium's N pole is also, of course, attracted to the bar magnet's south pole.)

Ahhh, but you see, then your iron magnet isn't really a true magnet, it is simply a piece of iron that has had its magnetic field aligned (a temporary magnet), much like if you connect a paper clip to a magnet for a few days, that paper clip will then still exhibit a magnetic field even after disconnecting the magnet from the clip. It will probably last a few minutes/hours as well.

Well all iron magnets are what you would say are "temporary." Left on their own, a ferromagnet will retain it's magnetic properties for a good while but they are susceptible to realignment of their domains by strong magnetic fields (which are how they are often made in the first place), annealing, or even by physical shock.

Then the same is true for all magnets. Even those neodymium magnets will do that under a strong enough external field.

 

[jagec]

Originally posted by: silverpig

Then the same is true for all magnets. Even those neodymium magnets will do that under a strong enough external field.

Yup, that's magnetism for you.