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Topic: Magnetism question  (Read 14814 times)

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Corvettaholic

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Magnetism question
« on: April 22, 2004, 06:36:11 PM »
OK, I think this fits under physical chemistry. As I understand magnetism, it involves aligning the electron spin of most of the atoms in a material, such as iron. Once all the electrons are spinning the same way (I don't know much about how this works), it will have a positive and negative end. Can someone explain why in simple terms?

Now for electromagnets, as you apply more current, not voltage, to a coil of wires over a ferrous core, the strength of the magnetic field will increase. I think you get more flux lines or something like that. Problem with adding additional current, is added heat, and you're likely to melt the insulation of the wires and short out the coil to the core. What would be a better way to add more current to a coil, and why does flowing electrons produce so much heat? Has something to do with resistance, right? Cause superconducters are really good at conducting (hence the name), and produce neglible heat, which means theoretically.. I could cram a lot more power through a liquid nitrogen cooled wire?

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Re:Magnetism question
« Reply #1 on: April 22, 2004, 06:42:06 PM »
Some large electromagnets use water to cool them, just pump it around the insulated wires. The reason why a magnetic substance will strengthen a magnetic field is because the initial magnetic field aligns the atoms of the substance.
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Corvettaholic

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Re:Magnetism question
« Reply #2 on: April 22, 2004, 06:51:25 PM »
I know having a core has to do something with permeability, which I guess how responsive a material is to a magnetic field, and air has a lot worse permeability than iron. So, logically, really permeable materials (as far as magnetics go) is the same as being ferrous. What else besides iron is ferrous? I've seen water cooled magnets before, such as in a MRI machine, but I'm wondering about a cryo-cooled one. Can I make iron become a superconducter by using liquid nitrogen? I read an article once about a superconducting magnet that levitated a frog, cause apparently you can temporarily induce magnetism in DNA, protein, and water. And living things have plenty of those!

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Re:Magnetism question
« Reply #3 on: April 22, 2004, 07:00:15 PM »
Levitating the frog wasn’t magnetism, it was diamagnetism, but it only exists strongly in some substances such as polyatric graphite and bismuth. Diamagnetism is a property where a substance actually reflects a magnetic field, pushing it away from the origin of the magnetic field. To levitate a frog you need an immensely strong electromagnet. But you can make an ok electromagnet that will run for about 6 bucks an hour in electricity if it’s water-cooled.
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Corvettaholic

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Re:Magnetism question
« Reply #4 on: April 22, 2004, 07:03:45 PM »
Well the magnet they used had something to do with a ceramic disk and liquid nitrogen. Neat stuff. I didn't know ceramics had anything to do with magnetism, maybe I should look into that. Dimagnetism was the thing I was looking for, just couldn't think of it. I thought dimagnetic just meant that something could be very temporarily magnetized?

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Re:Magnetism question
« Reply #5 on: April 22, 2004, 07:06:50 PM »
Your thinking of temporarily aligning the magnetic domains as an electromagnet does when it has an iron core.
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Corvettaholic

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Re:Magnetism question
« Reply #6 on: April 22, 2004, 07:14:21 PM »
Ah yes, but I always thought that just by being in a magnetic field you can do that. The core is in a magnetic field, and thats really close to the most flux lines. If you have a really freaking strong field, you can probably reach out and touch something a lot further away. Why is it that the core needs to be in the middle of the coil, as opposed to surrounding the exterior? Gets more flux lines that way?

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Re:Magnetism question
« Reply #7 on: April 22, 2004, 08:23:54 PM »
Yeah, the field is more intense in the center. You can calculate the distance by using the inverse square law.

Strength at position = Original strength / Distance2
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Corvettaholic

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Re:Magnetism question
« Reply #8 on: April 23, 2004, 11:54:23 AM »
Which is why my hard drive rare earth magnets can smash fingers up close, but a couple inches away they're pretty much useless. To increase the range of a magnetic field, thats dependent on the size of the magnet, not the material, right?

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Re:Magnetism question
« Reply #9 on: April 23, 2004, 12:21:27 PM »
The material affects how strongly it can be magnetised
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Corvettaholic

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Re:Magnetism question
« Reply #10 on: April 23, 2004, 12:38:04 PM »
Right, with better materials if you take a gauss meter to the surface, you're going to get a higher reading. But in a rare earth magnet, sure you can register 3 teslas of field strength, but a couple inches away it drops to some 400 gauss. Piddly. I think the strength weakening over distance involves a cube in the function, not a square. If the field strength over distance decreases by the cube of the distance (1 inch would be 1X weaker, 2 inches would be 8X weaker, 3 inches would 27X weaker), then how does increasing the size balance this out? You'd need a massive magnet to reach out and touch something 5 feet away!

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Re:Magnetism question
« Reply #11 on: April 23, 2004, 12:41:55 PM »
Yes you would need a huge magnet to affect something strongly. I am sure it is a square of the distance.
« Last Edit: April 23, 2004, 12:45:23 PM by Scratch- »
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Corvettaholic

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Re:Magnetism question
« Reply #12 on: April 23, 2004, 12:48:21 PM »
Well maybe it is square, I keep thinking cube for some reason. Regardless, its gonna be a huge magnet. Before they went out of business, forcefield.com sold a rare earth magnet in the shape of a 1 inch thick, PLATE. Get two of those together and you can smash stuff real good, including body parts. How would you store a really strong magnet like that without everything in your garage flying at it?

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Re:Magnetism question
« Reply #13 on: April 23, 2004, 12:50:22 PM »
You wouldn’t put it in your garage. Get between that and your lawn mower and they’ll have to scrape you off with a spatula (a plastic spatula).  ;D
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Corvettaholic

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Re:Magnetism question
« Reply #14 on: April 23, 2004, 03:40:35 PM »
I can't really think of any good uses for a permanent magnet that big. A) too expensive and B) too dangerous. Well there's always the entertainment factor, but I'm trying to think of a project I could use it for.

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