what are magnetic field lines?

You’ll need iron filings, a piece of paper, a piece of plastic sheeting and a bar magnet. It’s important to remember the plastic sheet in this experiment..unless you’ve got all day to pick filings off a magnet!

1. Take the piece of paper and sprinkle iron filings onto it as shown in the picture here. See how they scatter quite naturally?

2. Now, take a bar magnet, and lay a piece of plastic sheet over the top of it. Sprinkle the iron filings over and ...hey presto! magnetism in action - with all the field lines too.

Magnetic field lines show the direction and strength of a magnetic field. The closer they appear together, the stronger is the field. They are like the height contours on a map, they don't really exist but are a convenient way to illustrate the (invisible) magnetic field.