Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 17/04/2008 22:56:25

Title: Do Magnets Generate Heat ?
Post by: neilep on 17/04/2008 22:56:25

Hi There,

I'm Neil !...and you are ?

See these magnets :

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Nice eh ?

Nice and shiny and all magnety !

I saw a program where they were showing how they make those little gas cylinders....(the kind that power paint ball guns)...anyway..they used a very very strong magnetic field to heat the portion (shown) of the cylinder up to red hot !..I can't remember why...it was THAT enthralling !!

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How does a magnetic field produce heat ?....is there heat being generated in the magnets above ?

Thanks..ta...cheers


Neil
xxxxxxxx

mwah mwah mwah mwah

Title: Do Magnets Generate Heat ?
Post by: another_someone on 18/04/2008 02:18:54

A varying magnetic field (not a constant magnetic field) will induce an electric current in a conductor, and an electric current can produce heat.

Title: Do Magnets Generate Heat ?
Post by: daveshorts on 18/04/2008 08:58:25

Also just changing the magnetisation of a piece of steel one way and then the other will produce heat as some energy is lost in tehr process. This is one of the reasons that if you feel a transformer it will be warm even if you aren't drawing any current through it.

Title: Do Magnets Generate Heat ?
Post by: lyner on 18/04/2008 10:18:17

It's called inductive heating. The same principle as some cooking hobs.
If you put a metal (it has to be a conductor, so other utensils won't work) in a strong alternating field there are enormous currents ('eddy currents')  induced which produce heat.
transformers, mentioned above, are made with laminated  cores (each lamina is insulated from the next) to reduce the effect of eddy currents. The more current passing through the transformer, the hotter it will get.  A 'good' transformer will not get very warm off-load because its self inductance will be high enough to keep the leakage current very small.
Big, power distribution, transformers are full of circulating oil and have cooling tubes outside to dissipate this heat or they would melt, despite the laminations.

Title: Do Magnets Generate Heat ?
Post by: neilep on 18/04/2008 16:00:27

THANK YOU very much to you all for these great posts.

Now I understand. ( I hope it lasts  [;)])

Title: Do Magnets Generate Heat ?
Post by: syhprum on 18/04/2008 21:46:25

to test a large transformer you test the copper loss first with the secondary short circuited and a low voltage applied to the primary.
then you measure the iron loss with the secondary open circuited and add the two together.
at least that is what I was taught at school sixty years ago but techniques may have become more subtle since then

Title: Do Magnets Generate Heat ?
Post by: Soul Surfer on 21/04/2008 18:46:29

You can also use magnetism to generate cold! if you magnetise a paramagnetic substance by putting it in a strong magnetic field it generates a bit if heat.  when you remove the magnetic field paramagnetic substances loose their magnetism so if you magnetise them and cool them down very cold with liquid helium and then remove the magnetic field they get colder and can go down to millionths of a degree K  "magnetic refrigerators" are used to generate extremely low temperatures to test out very low twmperature phenomena.