Around every magnet there is a magnetic force field. If you move a magnet
over a second one, you can feel the effects of the force, and how the
force varies, depending on the relative position of each magnet. Can you
actually see this force field? The direct answer is no, but you can certainly
see the effects.
Seeing the effects of a magnetic force
One way of doing this is by using a small magnetic compass. Place a bar
magnet on a piece of cardboard and move the compass around it. You will
observe that the compass needle rotates depending on where it is in relation
to the magnet. To get a better idea, place the compass at one end and
then mark where the needle points. Move the compass so that the end nearest
the magnet is at the point you just made, then continue. Repeat the process
by starting from other positions around the magnet. You have actually
followed a few of the field lines.
a picture of the whole field
By placing a bar magnet under a piece cardboard and sprinkling iron
filings on top, with gentle tapping you will see the field lines being
marked out by the alignment of the iron filings. Look carefully at
the filings - you will notice that some are standing up; this is because
the field lines are all round the magnet, not just in a flat plane.
Every tiny piece of iron becomes a magnet with a North and South end,
each lining up along the field lines. A horseshoe magnet is similar,
though the magnetic field is stronger at the ends where the North
and South Poles are close together.
How does a magnet attract a non-magnet?
Place an ordinary iron nail under a piece of card and sprinkle some iron
filings on top. There will be no field lines, showing that the nail is
not magnetised. Move a magnet under the card, towards the nail. You will
observe a magnetic field begins to develop around the nail; this happens
because the field of the magnet induces the magnetic domains in the nail
to line up, a process called magnetic induction. If you tried the same
thing with a block of wood instead of a nail, there would be no induction
because the wood has no magnetic domains.