Plotting Magnetic Fields (Cambridge (CIE) O Level Physics): Revision Note

Plotting Magnetic Field Lines

• In your 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

Magnetic Field Shown Using Iron Filings

Iron filings can be used to plot a magnetic field

• 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

Magnetic Field Shown Using Plotting Compasses

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