Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Tim Haak on 26/05/2008 13:30:45

Title: Why do magnets attract unmagnetised pieces of iron?
Post by: Tim Haak on 26/05/2008 13:30:45
Tim Haak  asked the Naked Scientists:

Hi

My question is essentially why do magnets stick to non magnetized materials.
 
Like magnetic poles repel and unlike attract. Though in a piece of metal like iron that is not magnetized it should, from what I understand, have lots of randomly orientated magnets. When this piece of iron is magnetized these are aligned in a certain direction.
 
So why, when this piece of irons is not magnetized, is a magnet attracted to it, since its randomly magnetized it should equally repulsions and attractions cancelling itself out. Yet both poles can be attracted to it. What is happening?

Tim Haak

What do you think?
Title: Re: Why do magnets attract unmagnetised pieces of iron?
Post by: lightarrow on 26/05/2008 15:39:42
Quote from: Tim Haak  on 26/05/2008 13:30:45
Tim Haak  asked the Naked Scientists:

Hi

My question is essentially why do magnets stick to non magnetized materials.
 
Like magnetic poles repel and unlike attract. Though in a piece of metal like iron that is not magnetized it should, from what I understand, have lots of randomly orientated magnets. When this piece of iron is magnetized these are aligned in a certain direction.
 
So why, when this piece of irons is not magnetized, is a magnet attracted to it, since its randomly magnetized it should equally repulsions and attractions cancelling itself out. Yet both poles can be attracted to it. What is happening?

Tim Haak

What do you think?
The effect is called "induction" and is present for coulombian force too. The magnetic field generated from the magnet alines the atom's (or groups of atoms) magnetic moments in such a way that the two fields become opposite and so magnet attracts the piece of iron and the other way around.
Title: Re: Why do magnets attract unmagnetised pieces of iron?
Post by: chris on 27/05/2008 09:21:31
Just to say what lightarrow has already writte but in a slightly different way:

The field from the magnet aligns the magnetic dipoles (spins of the electrons) of the unmagnetised iron so that they match those of the magnet itself. This turns the piece of iron into a surrogate magnet, and so its north and south poles are the same as the magnet and hence the two stick together.

Chris
Title: Why do magnets attract unmagnetised pieces of iron?
Post by: lightarrow on 27/05/2008 12:57:26
You have said it better.  [:)]