Conservation of energy question with demagnetized magnets

In summary: When two ferromagnets are some distance apart and then raised above their Curie temperatures, there is more heat generated when they are further apart.
  • #1
Zet
1
0
I have a conservation of energy question I’ve asked about elsewhere but I didn’t get a fully satisfying answer.

I hoping someone here can help.

TIA
http://wedgecircles.com/images/384_newmpe01.gif​
Say you have two magnetically aligned magnets close to one another but some distance apart. There is a certain amount of potential energy between them. If they are allowed move they will set each other into motion due to mutual attraction. There will be an increase in kinetic energy and an equal decrease in potential energy.
http://wedgecircles.com/images/384_newmpe02.gif​
Now, say, there are two chemicals in a packet nearby and when these chemicals are exposed to one another thermal energy is generated (there is a decrease in chemical potential energy and an equal increase in thermal energy). And, say, the amount of thermal energy generated is greater than the Curie temperature of the two ferromagnets. (There are no other strong magnetic fields nearby in this closed system.)

If the chemicals are exposed to one another before the magnets are allowed to set each other into motion then the amount of potential energy between them is gone. However, if the chemicals are exposed to one another after the magnets have set each other into motion the kinetic energy (that came from an equal decrease in potential energy) is not gone.

So, in the end, after ferromagnets have been raised above their Curie temperatures, there must be more of another form of energy (such as thermal energy) in the first case and less of another form of energy (such as thermal energy) in the second case.

Is there more thermal energy in the end in the first case and less thermal energy in the end in the second case?

(One possible way to resolve this is to set the amount of potential energy between the two magnets at the start at 0. This way, in the first case, when the potential energy between them is then gone, 0 amount of potential energy becomes no potential energy. However, this does resolve the conservation of energy analysis in the second case because the positive amount of kinetic energy remains but the offsetting decrease in potential energy (negative potential energy) is then gone.)

So, when two ferromagnets are some distance apart and then raised above their Curie temperatures is more heat generated when they are further apart or is more heat absorbed when they are closer together?

It seems to me one or the other must be the case for energy to be conserved.

Is it the case?

?
 
Last edited:
Physics news on Phys.org
  • #2
Welcome to PF;
Where else did you ask the question (link please) and what was it about the answers that was unsatisfactory to you? It is unlikely that I'll be able to give you a satisfying answer, whether or not you are satisfied is not up to me - but I can help you think about your questions.

Potential energy has no absolute so you intuition about setting the initial potential energy of the magnets to zero is a good one.
Configurations have potential energy only in relation to some other configuration.

But you may have more luck thinking about whether a magnet is harder to demagnetize when it is inside a strong magnetic field.
If it is in a heat bath with temperature much higher than the Curie temperature, then the random jiggling of the magnetic domains would still be constrained by the magnetic field acting on those domains right? So the domains will tend to (try to) remain aligned to the field.

Also consider: the Curie temp is not the temp at which magnetism vanishes, but where the type of magnetism changes.
 
Last edited:
  • #3
Zet said:
(There are no other strong magnetic fields nearby in this closed system.)
But each magnet is in the magnetic fields of the other magnet. So why do you think they should demagnetize?
 

What is conservation of energy?

Conservation of energy is a fundamental principle in physics that states that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another. This means that the total energy in a closed system remains constant over time.

How does conservation of energy apply to demagnetized magnets?

Demagnetized magnets do not violate the law of conservation of energy. When a magnet is demagnetized, the energy that was stored in the magnetic field is transformed into other forms of energy, such as heat or sound. The total energy in the system remains the same, as energy cannot be lost or gained.

Can a demagnetized magnet regain its magnetic properties?

Yes, a demagnetized magnet can regain its magnetic properties through a process called remagnetization. This can be achieved by exposing the magnet to a strong magnetic field, which aligns the magnetic domains within the magnet and restores its magnetic properties.

Is there a limit to how many times a magnet can be demagnetized and remagnetized?

Yes, there is a limit to how many times a magnet can be demagnetized and remagnetized. Each time a magnet is demagnetized, its magnetic domains become more disordered, making it harder to restore its magnetic properties. Eventually, the magnet will reach a point where it cannot be remagnetized.

How does conservation of energy impact the use of magnets in everyday life?

Conservation of energy is an important consideration in the use of magnets in everyday life. Magnets are used in a variety of applications, such as electric motors and generators, and the principles of conservation of energy must be taken into account to ensure efficiency and proper functioning of these devices.

Similar threads

  • Electromagnetism
Replies
11
Views
1K
Replies
10
Views
843
  • Electromagnetism
Replies
5
Views
332
Replies
3
Views
494
Replies
1
Views
965
  • Electromagnetism
Replies
4
Views
1K
Replies
12
Views
2K
Replies
51
Views
1K
  • Electromagnetism
Replies
18
Views
2K
  • Electromagnetism
Replies
2
Views
1K
Back
Top