Ask A Scientist Physics Archive

name         sanya
status       student
grade        K-3
location     N/A

Question -   what is a magnet?
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Hi, Sanya.  You probably already know that magnets stick to some metals
and sometimes to each other.  It's kind of hard to explain what a
magnet really "is", though.

First, you need to know that magnets have "north" and "south" poles.
These names don't mean anything (like the poles of the earth).
Instead, they are just names.  When you point two magnets at each
other, "like" poles push each other away and "unlike" poles pull
towards each other.  So a "north" attracts a "south" but repels other
"north" poles.

Magnets are usually made of metal in some form.  Metals are usually
made of small crystals.  If you could look at these crystals in a
magnet from the inside, you would see that each one of these crystals
is a small magnet with its own poles.  So a magnet is really a bunch of
little magnets.  The big magnet doesn't act like a magnet until all the
little magnets are lined up the same way.

This is usually done by taking the metal piece that you are making into
a magnet, and placing it inside a REALLY STRONG magnet for a while.

Now for the hard part.  The crystals themselves don't move (at least
not much) when a magnet is made.  Instead, the metal atoms inside are
affected.  The way the atom is arranged is what makes the magnet act
like a magnet.

I've only talked about natural magnets.  You can also make a magnet
that can be turned on and off by running electricity through a coil of
wire wrapped around a piece of metal.  This is called an electromagnet,
and it is the basis of all the electric motors used in all the gadgets
all around us.

Sorry if this isn't a good explanation, but if you don't understand
completely, I encourage you to experiment.  This is a great way to
learn and is also a lot of fun!  All sorts of magnet kits, including
electromagnet kits and simple electric motor kits are available from
many sources, both online and in electronics stores, and will help you
learn more.

Have fun!

David Brandt, P.E.
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A magnet can be any material that keeps a magnetic field around itself.
There are many different types of magnets, made of amny different types of
materials, but the two most important are "Permanant magnets" and
"Electromagnets".


Permanant magnets are easy to find, and I suspect there are some in your
house, attached to the refrigerator.  These can be made of ceramics, metals,
or even rubber!  They are always magnetic, no matter what.


The second kind of magnets, "Electromagnets" are electrical devices that
only become magnets when electricity is put through them.  Most of these are
found in electric motors, where turning magnets on and off rapidly allows
them to spin.  If you have a fan in your house, you can bet there are
electromagnets inside!


Ryan B.
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Any two electrons travelling fast, side-by-side in the same direction,
have a mysterious force which pulls them towards each other.
This force is called magnetism.  (It seems a consequence of the truth of
special relativity.)
We say each moving electron makes a "magnetic field" which pulls on the
other electron.
Two parallel wires carrying electric current in the same direction also
weakly attract each other.
The electrons in the wire are travelling very slowly, but there are very
many of them,
so a noticeable magnetic force happens.

A "permanent magnet" is a piece of a special substance which makes a
magnetic field around it.
The special substance is usually a hard metal;
it makes this magnetic field by having
electrons trapped going around in tiny circles
in some of it's atoms.

Electric charge going in circles makes a magnetic field with North and South
poles.
Electrons moving along a coiled wired do it. (electromagnets)
Electrons travelling in short circular paths in a conductor do it.
(superconductors)
Electrons spinning in place also do it.  (permanet magnets)

It turns out that all electrons have a little spin all the time.
(I don't yet know why.  It seems to be a rather fundamental fact of life.
Maybe someday physicists will explain it.)
In atoms, most spinning electrons have best-buddies which spin the opposite
way,
cancelling out their little bit of magnetic field.
Some atoms have an "un-paired" electron with no buddy;
these atoms are strong little magnets.
If the substance is hard, the atoms can't move around easily.
All these magnetic atoms can get stuck in place facing the same way.
Then their magnetic fields (N & S poles) add up strongly
and reach well outside the piece of substance.

It's not too easy to explain a magnet well.
Electron spin, spin-pairing, ferro-magnetism vs. other magnetic behaviors,
and pinning of magnetic domains are pretty advanced ideas.
If you want a simpler idea, just imagine that
every magnet is full of electrons trapped going in little circles,
which push or pull on other nearby electrons
just because those are also going in circles.
(kind of weird, I admit...)

Jim Swenson

PS- I'd like to give a conceptual answer which mentions
the energy inherent in a magnetic field in empty space,
and that magnetic force attempts to minimize the volume of such exposed
field.
But I didn't grow up with traditions of ideas like that,
so I can't make them sound natural today.
Maybe someday.
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