# How can we determine if poles are North or South when viewing magnetic field lines formed by iron filings?

Iron filings can be used to visualize the magnetic field lines of a magnet.

For example, from Wikipedia:

$$\hspace{175px}$$,
The magnetic field of a bar magnet revealed by iron filings on paper. A sheet of paper is laid on top of a bar magnet and iron filings are sprinkled on it. The needle shaped filings align with their long axis parallel to the magnetic field. They clump together in long strings, showing the direction of the magnetic field lines at each point.

Question: When looking at magnetic field lines formed by iron filings, how can we determine which magnetic pole is North and which is South?

• I do not understand what you mean by "magnetised field lines". – Farcher Jan 4 '19 at 16:47
• Suppose I posted the same picture as you have without the 'N' and 'S' labels, how could you tell if I had turned the picture around? (This is just a hint, I don't have time to write an answer now.) – jacob1729 Jan 4 '19 at 23:05