Magnetic fields
Seeing the effects of a magnetic force field Seeing a picture of the whole field
How does a magnet attract a non-magnet?

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 field
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.

Field lines.
Seeing 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.
Click for larger image
Click for larger image

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.

Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission.

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