# Magnetic lines of force

1. Dec 9, 2008

### nottheone

Do magnetic lines of force actually exist and if so is there any proof of distinctive lines other than the classic magnet and iron filings on paper?

2. Dec 9, 2008

### Integral

Staff Emeritus
Have you ever seen or heard of a topography map? This is a map that shows the contours of the land, a contour line follows along a constant level of elevation. If you walk along a hill side there are no contour lines drawn on the ground. BUT the path of constant elevation is there.

The same with magnetic lines, we cannot see them but the quantity they represent is there. Now what do you think? Do magnetic field lines exist?

3. Dec 10, 2008

### p.tryon

This is a good question because Iron filings around a magnet are often used in schools and text books to introduce the notion of field lines. I have though about this too and come to the following conclusion (I stand to be corrected on this): The allignment of Iron filings is due to the magnetisiation of the individual filings; I don't think this proves that actual field lines exist. Field lines are a conceptual construction (like the example of contours on a map) intended to represent (rather than explain) the behaviour of a magnet.

4. Dec 10, 2008

### timmay

Fields are continuous; contour lines and field lines are merely discrete, representations of them.

Take for instance a hill and its representation on a map. The map shows discrete lines showing regions of the same elevation, and are (depending on the scale of the map) usually spaced at a certain interval of maybe 10m, 50m or 100m of elevation. But if you were to try and visualise the hill from those contour lines, you know that it's not just a series of steps; the surface of the land varies between those lines with a slope.

It's much the same with field lines and magnets. There is still a magnetic field between your 'field lines', it's just that the magnetic filings disperse in this pattern (probably as the previous poster suggest due the attraction of individual filings to its nearest filing). I'm willing to bet that as you reduce the filing size the less obvious those 'field lines' become.