Plotting Magnetic Fields (Cambridge (CIE) IGCSE Physics)

Plotting magnetic field lines

• In your IGCSE examination, you might be asked to describe a method of plotting the magnetic field around a bar magnet

• There are two principal ways of doing this:

  • using iron filings

  • using plotting compasses

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

Magnetic field lines using iron filings

Iron filings can be used to plot a magnetic field

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 on 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. This is the magnetic field line

• The direction of the field lines go from the north pole to the south pole of the magnet.

  • This is the same as the direction of the north arrow on the plotting compass, which points towards the south pole

• Repeat the process to create other magnetic field lines around the bar magnet

Using a compass to create magnetic field lines

Compasses can be used to plot the magnetic field around a bar magnet