1

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 30/01/2022 08:28:50 »

Thanks for that. I will seek out the more advanced explanations !  Although I'm actually 76 years old, the school level explanation will suffice for now. 

2

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 29/01/2022 21:15:26 »

Thanks guys for your excellent and detailed  replies.

I think I just need to get my head around the bit where  - energy is stored temporarily in the magnetic field.

3

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 29/01/2022 20:30:58 »

Again, I don't like that analogy. The table is not compressable by the weight of the book. The air between my magnets is compressable by the weight of the upper magnet - and would be if the lower magnet were not there.

4

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 29/01/2022 16:16:49 »

Over the years I have had many different answers to my question. However, I have never been totally convinced by the answers I got. Most of them quote text book Physics saying that there is no work done as nothing is moving ! If you have an explaination I would love to hear it.

5

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 04/12/2021 21:36:45 »

'quote'
A conventional copper electromagnet continually loses energy through resistance, and this loss must be overcome to maintain  the magnetic field.

Are you saying that all the electrical energy supplied to an electromagnet is lost to resistance and none of it used to create the magnetic field ?

6

Physics, Astronomy & Cosmology / Re: where does permanent magnet energy come from

« on: 04/12/2021 21:25:32 »

Not sure about the metal spring analogy. I can see that in compresing a metal spring the applied force can cause that energy to be stored in the atoms of the metal and when you remove the force compressing the spring that energy can be used to return the spring to it's original shape. In the 2 magnets situation there is an air gap between them so where is the energy used to close the gap between the magnets stored in order to be used to reinstate the gap ?

7

Physics, Astronomy & Cosmology / where does permanent magnet energy come from

« on: 04/12/2021 20:42:15 »

I have two toroidal permanent magnets which are fitted over
magnet.jpg (151.11 kB . 805x989 - viewed 4901 times)
magnet.jpg (151.11 kB . 805x989 - viewed 4901 times)a plastic tube with like poles facing each other.
Because of the magnetic repulsion the top magnet 'hovers' 20mm above the bottom one. I have had this pair
of magnets as an ornament in my workshop for more than 10 years and there is no discernable change in the
gap between them. The magnets are about 85mm in diameter, the central hole of the toroid about 50mm and they
weigh about 400g each.

My question is:
Where does the energy come from to support the top magnet against the force of gravity. Classical Physics seems to say that with the magnets in this static situation then no energy is involved and no work is done as
there is no movement or displacement. However, If I push the top magnet towards the lower one and release it, it
returns to it's 'hover' position. Clearly energy is required to do that. No matter how many times that is done, the permanent magnetism does not seem to be depleted.

As a thought experiment, if the bottom magnet was replaced with an electromagnet then electrical energy would be required to support the top magnet and if the power was removed the top magnet would drop. I realise that toroidal electromagnets have no external magnetic field but if bar magnets were used instead and constrained horizontally in a tube then the same would apply.