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Why magnet attract only metal ?

by ngkamsengpeter
Tags: attract, magnet, metal
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ngkamsengpeter
#1
Mar23-06, 01:35 AM
P: 194
I want to know that why magnet attract only metal but not all thing . Since all thing are made up of atom, what make the metal so difference so that it can be attract by a magnet ?
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Mk
#2
Mar23-06, 02:21 AM
P: 2,056
Magnets don't only attract metals, they attract and repel many things, usually you don't notice in everyday life.

Wikipedia

Something that is strongly attracted to a magnet is said to have a high permeability. Iron and steel are two examples of materials with very high permeability, and they are strongly attracted to magnets. Liquid oxygen is an example of something with a low permeability, and it is only weakly attracted to a magnetic field. Water has such a low permeability that it is actually repelled by magnetic fields. Everything has a measurable permeability: people, gases and even the vacuum of outer space.
ngkamsengpeter
#3
Mar24-06, 12:04 AM
P: 194
What is mean by permeability?

Chaos' lil bro Order
#4
Mar24-06, 12:15 AM
P: 683
Why magnet attract only metal ?

metals have little sectors in their structures that contain magnetic moments that can be attracted to or unattracted to a magnet depending on the polarization of the sectors relative to the magnet's polarization (opposites attract).

In general, compounds that are conductors (like metals) are easily magnetized, while compounds that are insulators (like plastics, glasses, woods) are difficult to magnetize. Although this is just a guideline and not absolute.
rachmaninoff2
#5
Mar24-06, 03:28 AM
P: 18
Quote Quote by Chaos' lil bro Order
Extremely powerful magnets can even attract strawberries for example, metal just happens to have 2-3 valence electrons extra per atom and the surface of metal has free charges that can easily be attracted by a magnet. Also, metals have little sectors in their structures that contain magnetic moments that can be attracted to or unattracted to a magnet depending on the polarization of the sectors relative to the magnet's polarization (opposites attract).

In general, compounds that are conductors (like metals) are easily magnetized, while compounds that are insulators (like plastics, glasses, woods) are difficult to magnetize. Although this is just a guideline and not absolute.
This is all dead wrong. Since when are free charges attracted to magnets?

Please refrain from "explaining" subjects which you know nothing about.
rachmaninoff2
#6
Mar24-06, 03:59 AM
P: 18
ngkamsengpeter:

When you have an individual electron, it behaves like a bar magnet (it has an intrinsic magnetic dipole moment). Usually electrons prefer* to pair up with another electron with the magnet pointing the other way - so the pair of electrons together has no magnetic dipole, they effectively neutralize each other (*this is because of the quantum mechanical principle of Pauli exclusion). In many atoms you have only such pairs of electrons, so the whole atom has no magnetic dipole. But for example, if there are an odd number of electrons* (example Alumnium, 13 electrons), there is at least one 'unpaired' electron, at the whole atom will have the magnetic dipole of this one electron; the whole atom will act as a bar magnet and respond to external magnetic fields. This is an example of paramagnetism.
*this is not necessary but common

This is a very weak effect - aluminum is attracted to magnets, but only slightly. When you deal with everyday magnetic materials, such as iron, a far stronger effect is involved.

Instead of one atom acting individually as a little bar magnet, occasionally you have millions of atoms deciding to align with each other and reinforce each others' magnet dipoles - a magnetic domain. These are basically much bigger bar magnets, and are responsible for the strong magnetizibility of ferromagnets like iron. This can happen (the magnetic domains) if certain criteria regarding the solid's structure and bond lengths are satisified.
rachmaninoff2
#7
Mar24-06, 04:08 AM
P: 18
Quote Quote by ngkamsengpeter
What is mean by permeability?
It basically just tells you how a material responds to a magnetic field.

If you apply a magnetic field to an object, any magnetic atoms inside will respond to it and move to a new configuration, possibly causing a new magnetic field of their own, distinct from the field you're applying. If the permeability is a large number, it gets magnetized parallel to the external field, and there is attraction. If the permeability is small enough, it actually magnetizes opposite to the external field (diamagnetism) and is repelled; this is a very weak effect and can be observed with pure water.

see also http://en.wikipedia.org/wiki/Permeab...romagnetism%29
Chaos' lil bro Order
#8
Mar24-06, 04:49 PM
P: 683
Quote Quote by rachmaninoff2
This is all dead wrong. Since when are free charges attracted to magnets?

Please refrain from "explaining" subjects which you know nothing about.

Aren't surface charges more likely to be attracted to magnets then volume charges inside the object?
Are you refuting my whole post or just a piece of it?
rachmaninoff2
#9
Mar24-06, 06:05 PM
P: 18
Are you refuting my whole post or just a piece of it?
Charges aren't attracted to magnets, period.

"Metals have little sectors" - most don't have long-distance ordering in the form of magnetic domains, only ferromagnets do (iron, cobalt, etc.).

"magnet's polarization" - magnets are not generally polarized.

"In general, compounds that are conductors (like metals) are easily magnetized, while..." - is not, 'in general'. There's no reason to expect it to be - the physics of ferromagnetism has nothing to do with conduction. Look at this short list of ferromagnetic materials - you have both very conductive metals and very insulating metal oxides.
Another fallacy with this 'rule' - all the non-magnetic examples you've listed are amorphous, they do not have a regular crystalline structure and cannot be expected to be ferromagnets. An example of insulating non-metal ferromagnet would be carbon - in its novel nanofoam allotrope.


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