A question about permanent magnets

Click For Summary

Discussion Overview

The discussion centers around the longevity and behavior of permanent magnets, including their energy loss over time, the conditions under which they may lose their magnetic force, and their functionality in environments such as space. Participants explore various factors affecting magnet strength, including temperature, physical impact, and external magnetic fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that permanent magnets gradually decrease in strength over time due to various factors, including temperature and physical impacts, but this process is typically very slow.
  • Others argue that the term "wear" may be misleading, as the magnetic domains can remain stable under normal conditions, and the magnet's strength is designed to last.
  • Participants inquire about specific conditions that may lead to energy loss, such as collisions with metal objects and whether simply sitting still affects a magnet's strength.
  • There is a discussion about the concept of "domains" in magnets, with questions regarding the physical changes that occur when these domains are realigned.
  • Some participants mention the "curie point" as a critical temperature threshold above which a magnet loses its ferromagnetic properties.
  • Questions arise about the functionality of permanent magnets in space, with some asserting that they do not rely on Earth's energy and will work in free space.
  • Concerns are raised about the potential for demagnetization in applications such as motors, where extreme temperatures and physical impacts could affect magnet strength.
  • Participants speculate on the longevity of permanent magnets in energy generation applications, questioning how long they would retain their magnetic properties under continuous use.

Areas of Agreement / Disagreement

Participants express a range of views on the longevity and behavior of permanent magnets, with no clear consensus on the specifics of energy loss or the conditions that lead to demagnetization. Multiple competing perspectives remain regarding the factors influencing magnet strength and functionality.

Contextual Notes

Limitations include varying definitions of terms like "fixed" magnets, the lack of consensus on the impact of external factors on domain alignment, and the dependence on specific conditions that may not be fully explored in the discussion.

Who May Find This Useful

This discussion may be of interest to individuals studying magnetism, those involved in engineering applications using permanent magnets, and anyone curious about the practical implications of magnet behavior over time.

linux kid
Messages
101
Reaction score
0
Does a permanent magnet ever loose it's energy or decrease over time? I read somewhere that a "fixed" magnet's energy will dissipate in time as it does work. I don't know what they mean by fixed.

Also, will a permanent magnet work without the Earth's energy (eg. in space).
 
Physics news on Phys.org
The short answer is yes it will. Here is a post that sums it up:

'Wear' is a somewhat misleading term. Permanent magnets gradually decrease in strength, but this has very little to do with usage. The "life" of a permanent magnet depends on many factors. Naturally occurring forces conspire to knock the little domains out of alignment. But this is normally a very slow process. Temperature is a major player in this process. The higher the temperature, the faster this process will occur. Extreme heat [surpassing the curie point] will immediately randomize the domains. A sharp blow can also knock domains out of alignments, as can other nearby magnetic or electrical fields. Radiation can also knock domains out of alignment. But again, under normal conditions, neither your fridge or you will live long enough to watch the little fellow fall to the floor in exhaustion. At the quantum leve [e.g., electrons] magnetism is eternal.
https://www.physicsforums.com/showpost.php?p=1195930&postcount=5
 
Under what conditions will a permanent magnet loose it's magnetic force:

1: I have read that the magnet will lose some energy when it "hits" the metal item. Is this the only way it will lose it's energy?

2: Will it degrade by simply sitting?
 
linux kid said:
Under what conditions will a permanent magnet loose it's magnetic force:

1: I have read that the magnet will lose some energy when it "hits" the metal item. Is this the only way it will lose it's energy?

2: Will it degrade by simply sitting?

I thought the quote in my first reply addressed number 1. The domains will be realigned by heat, shock, or the influence of a demagnetizing magnetic field - permanent magnets have a characteristic called coercivity, which is basically its ability to withstand being demagnetized.

For number 2, if you remove all the external aspects that conspire to knock the domains out of alignment, is there any reason for the domains to be realigned?
 
What does "domain" mean here?

Also, when you say heat, is there a certain threshold or referencepoint? For example does room temperature count or are we talking higher temps?
 
Last edited:
linux kid said:
What does "domain" mean here?

Also, when you say heat, is there a certain threshold or referencepoint? For example does room temperature count or are we talking higher temps?

More info on domains can be found here:
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/ferro.html#c4

Yes there is a certain threshold called the curie point. At temperatures above the curie point, the material loses its ferromagnetic characteristic. For a list of curie temperatures read this:
http://en.wikipedia.org/wiki/Ferromagnetism
 
linux kid said:
Does a permanent magnet ever loose it's energy or decrease over time? I read somewhere that a "fixed" magnet's energy will dissipate in time as it does work. I don't know what they mean by fixed.

Also, will a permanent magnet work without the Earth's energy (eg. in space).

A permanent magnet looses energy very slowly over time. Thats the point though, its supose to keep its magnetic field
 
hover said:
A permanent magnet looses energy very slowly over time. Thats the point though, its supose to keep its magnetic field

Even without the external aspects that ranger listed above?
 
Last edited:
Does all this mean that as long as the domains stay in their original position the magnet will not be affected?
 
  • #10
Even without the external aspects that ranger listed above?
If none of these external factors are present, then there isn't any reason for the domains to get realigned.
Does all this mean that as long as the domains stay in their original position the magnet will not be affected?
Yes.
 
Last edited:
  • #11
Thanks much everybody.
 
  • #12
Oh, I have one more :):

Do permanent magnets rely on the Earth (will they work in space)?
 
  • #13
linux kid said:
Oh, I have one more :):

Do permanent magnets rely on the Earth (will they work in space)?

It will also work in space (free space). Everything has measurable permeability.
 
  • #14
What exactly happens when these domains change direction. Is the something physicaly occurring inside the domains? I'm finding it hard to find info on this.
 
  • #15
Many motors use permanent magnets (usually rare Earth strong type). In this cases, there a few things that can demagnetize them, and thus must be avoided:

-extreme temperature (Currie temperature I think?)
- Too high of current (and thus magnetic field from the coils)
- damage from dropping, bashing, or even disassembling the magnets.

So, although permanent magnets can quickly become demagnetized, in such an application, you have to know at what temperature, current, etc this occurs, and design your system to avoid it.
 
  • #16
We have already went over that MedievalMan. Nonetheless your input is appreciated. My last question is right on top of yours.
 
Last edited:
  • #17
Nevermind, I have found a good resource.
 
  • #18
If I were to put two opposing magnets next to each other of equal strength would either be affected? I understand that if one were stronger it would destabilize the other.
 
  • #19
how about if you built an electric generator with "permanant" magnets?
how long would it last? I'm trying to cut down on costs on energy but i need some alternatives so far i have solar energy, and thinking most about kinetic energy(magnets) how long would it stay permanent and will we be alive by the time it dies?
 
  • #20
I was wondering about that too. Would the magnets loose their power if under constant collision of opposite fields that they would experience in a motor. Based on what is being said here, i am guessing that they should retain their power, but then again they might not. I need to confirm this because magnets are expensive.
 

Similar threads

High School Permanent magnets and energy question
  • · Replies 16 ·
Replies
16
Views
3K
High School Basic Straight Line Permanent Magnet Accelerator
  • · Replies 3 ·
Replies
3
Views
2K
Graduate PPMT, Magnetic Flux Switch, electro-permanent magnet generator
  • · Replies 8 ·
Replies
8
Views
4K
Graduate Forces between a Solenoid and an External Permanent Magnet
  • · Replies 6 ·
Replies
6
Views
3K
High School Why does a magnet attract metal objects?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Speed of magnetic flux propagation?
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Permanent magnets still an open problem
  • · Replies 6 ·
Replies
6
Views
2K
Graduate Field Energy of Permanent Magnets vs. Magnetic Monopoles
  • · Replies 27 ·
Replies
27
Views
4K
High School Experiment issues (electromagnetism)
  • · Replies 42 ·
2
Replies
42
Views
4K
High School A Magnetic Misconception on Divergence 0/Closed Field Lines?
  • · Replies 3 ·
Replies
3
Views
1K