What happens to magnetic fields when poles are near each other?

  • Thread starter Newtype
  • Start date
39
0
What happens when same magnetic poles (i.e., NN or SS) are next to each other for say an hour or more - will the magnetic fields of those magnets become weaker or stronger?

What happens when different magnetic poles (i.e., NS or SN) are next to each other for say an hour or more - will the magnetic fields of those magnets become weaker or stronger?

Please provide formulas and examples, thank you.
 
62
1
Simple question, complicated answer:

For practical purpose, in the attracting pole case, nothing interesting happens. The field lines merge and the two smaller magnets effectively behave as a larger magnet. For practical, permanent magnets, usually nothing happens to the magnets themselves. (more on this in a moment).

In the repelling case, the field lines bend away from each other, and the magnets create a repelling force. Again, in most cases, nothing interesting happens to the magnet.

Okay, now let's step away from the "most cases" qualifier.

Magnets have two key properties: remnance and coercivity. Remnance is a description of how intense a field the magnet produces. Coercivity is a description of how hard it is to demagnetize the material (actually, to 50% reverse-magnetize it, but for our purposes we can be a little sloppy). Now, as long as we don't exceed the coercivity, nothing will happen - and for various measurements we have done, time is not a function in the equation. Leave it for an hour, two hours...there will be no useful difference. Temperature is a big factor - warming a magnet up can reduce the coercivity.

Having said all that, your typical rare-earth magnets have very high coercivities, and are really hard to demag with another permanent magnet. Alnico magnets, on the other, are notoriously easy to flip or change.

No formulas, but there are some examples there. Hope it helps.
 
39
0
Thank you, MagnetDave. So basically I could design a six magnet vehicle engine. This would be a good way to reduce global warming and dependence on oil. Here's how this machine I wrote up the plans for works: Two inner moving bar magnets (mounted in frames) repel each other along tracks. Next, two outer stationary bar magnets repel the two inner moving bar magnets back to each other. This process works infinitely. While the inner moving bar magnets are moving they each turn a gear. Each of those gears turns an axle and each of those axles turns a horseshoe magnet inside of a coil of wire generating electricity. Thus electricity can be produced forever using this machine. It would require diodes to convert the alternating currents into direct currents. With power amplifiers this machine might possibly electrically power a house (each house might have one of these generators and modified if desired) and a vehicle (a person might have his/her car powered by one of these generators). Would this six magnet vehicle engine work? If so, how long?

NS---SN---NS----SN
___Gear__Gear
____Axle__Axle
____NS___SN
____Coil__Coil
 
Last edited:
I coincide with above explanations. If we take two bar magnets near to each other, then like magnet poles repel each other and dislike poles attract each other.-narasimha charyulu
 

Integral

Staff Emeritus
Science Advisor
Gold Member
7,185
55
So basically I could design a six magnet vehicle engine. This would be a good way to reduce global warming and dependence on oil. Here's how this machine I wrote up the plans for works: Two inner moving bar magnets (mounted in frames) repel each other along tracks. Next, two outer stationary bar magnets repel the two inner moving bar magnets back to each other. This process works infinitely. While the inner moving bar magnets are moving they each turn a gear. Each of those gears turns an axle and each of those axles turns a horseshoe magnet inside of a coil of wire generating electricity. Thus electricity can be produced forever using this machine. It would require diodes to convert the alternating currents into direct currents. With power amplifiers this machine might possibly electrically power a house (each house might have one of these generators and modified if desired) and a vehicle (a person might have his/her car powered by one of these generators). Would this six magnet vehicle engine work? If so, how long?

NS---SN---NS----SN
___Gear__Gear
____Axle__Axle
____NS___SN
____Coil__Coil
One word.

No.

Discussion of PM machines is against site guidelines.

Thread locked.
 

Related Threads for: What happens to magnetic fields when poles are near each other?

Replies
18
Views
5K
Replies
22
Views
8K
Replies
17
Views
10K
Replies
6
Views
4K
Replies
12
Views
2K
Replies
2
Views
1K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top