The below mentioned article provides an experiment to determine the area of magnetic field of a bar magnet in a horizontal plane.
The space surrounding a magnet where the force of attraction or repulsion due to that magnet is felt, is called magnetic field of that magnet. From theoretical consideration the magnetic field of a magnet is extended upto infinity. In practice, however, the magnitude of the force falls off rapidly with distance and becomes too small beyond a few metres.
Magnetic field is not produced by magnets alone. It is produced around a conductor when electric current flows through the same.
The area of the magnetic field of a bar magnet in a horizontal plane can be determined by the following experiment:
Place a plate of glass over a bar magnet so that the magnet is at the centre of the glass plate. Put a sheet of paper on the glass plate and sprinkle iron filings on it. Due to inductive action of the magnet, each filing becomes magnetised and begins to behave like a very small magnet.
If the glass sheet is now tapped gently, the filings rotate and arrange themselves in a particular manner as shown in fig. 47. The area up to which the filings have arranged themselves properly is the area of the magnetic field. Beyond this area the filings are arranged disorderly.