28 April 2020 Physics
Mbusa Edson

Plotting a Magnetic Field


  • In your IGCSE examination you might be asked to describe a method of plotting the magnetic field around a bar magnet.
  • There are two principle ways of doing this.

Using Iron Filings

  • Place a piece of paper on top of the magnet.
  • Gently sprinkle iron filings on top of the paper.
  • Now carefully tap the paper to allow the iron filings to settle on the field lines.

Using Plotting Compasses

  • Place the magnet on top of a piece of paper.
  • Draw a dot at one end of the magnet (near its corner).
  • Place a plotting compass next to the dot, so that one end of the needle of the compass points towards the dot.
  • Use a pencil to draw a new dot at the other side of the compass needle.
  • Now move the compass so that it points towards the new dot, and repeat the above process.
  • Keep repeating until you have a chain of dots going from one end of the magnet to the other. Then remove the compass, and link the dots using a smooth curve – the magnetic field line.
  • The direction of the field line is the same as the direction of the plotting compass.
  • You can now repeat the whole process several times to create several other magnetic field lines.