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Q: Magnetism questions. ( Answered ,   1 Comment )
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 Subject: Magnetism questions. Category: Science > Physics Asked by: centure7-ga List Price: \$15.00 Posted: 07 Jan 2006 19:05 PST Expires: 06 Feb 2006 19:05 PST Question ID: 430559
 ```I have a hefty 2x2x4 inch neodymium magnet with poles on opposite sides. It can easily lift 100Ibs. 1) If my magnet could lift 100kg using the south pole (2"x2" area), approximately how much could a 2x2x8 magnet made of the same material lift? What about a 2x2x126000 inch magnet? Does that proportion hold at any scale? 2) I take one of those classic 5-pound circular disc/plate/barbell weights and put the magnet where the hole is for the barbell (very carefully and using well-planned methods!). On the other side of the weight plate, where the hole is for the barbell, it seems that even though I have a clear line of sight to the extrodinarily powerful magnet, that the field has been catastrophically reduced by the surrounding metal... if I hold a metal ball the exact same distance away from the magnet, I won't feel the magnet have an intense of a tug. Is my feeling accurate? If so, how has the magnet changed? Is it now as if the entire 5-pound weight is the north pole of the magnet, reduced in power proportional to its mass and reduced in intensity over the surface area of the weight?```
 ```1) Yes. the power of the magnet will increase, and will be APROXIMATELY proportional to the cross-section. 2) The magnet did not change. Magnetic field around the magnet changes whenever you bring a new (magnetic) object to the area (and it does it with speed of light = quickly). The 'pull' depends on the magnetic field at the location of the object. Exact solution eo equations which describe the field is complex, but notion of 'magnetic flux' gives a simple and intuitive APROXIMATION to the field and forces: One has to imagine a circuit, as if 'something' (flux) is flowing from one pole to another. In this analogy, air has high resistance, iron low, and flux (as current would) tries to go by path of low resistance. Here is the picture of the fluxlines: www.magnetweb.com/ Sect4A.htm Ignore the stuff on magnetisation. Picture of fluxlines is an example we want. If you put a piece of iron in the gap and are pulling it out, you are increasing the 'resistance'. That is resisted by the magnetic force (as if the fluxlines are rubber bands). SEARCH TERMS : magnetic circuits references http://en.wikipedia.org/wiki/Magnetic_circuit More examples of flux lines [ http://images.google.com/images?svnum=10&hl=en&safe=off&client=opera&rls=en&q=magnetic+field&spell=1 ] Rating appreciated. Hedgie```
 centure7-ga rated this answer: ```Very fascinating stuff. I wasn't aware that magnets have a "circuit design" acting similarly to electric circuits. The links were interesting. Thanks!```
 ```Sorry for not producting a picture, but: The reason a sheet of metal is both attracted to a magnet and blocks magnetic field from propagating beyond it is because a sheet of metal causes the magnetic field lines to bend and travel INSIDE the metal. Go find a good picture and you will understand it.```