To map the magnetic field around a bar magnet using a small compass, begin by placing the magnet flat on a sheet of paper and lightly tracing its outline to keep it in the same position throughout the process. Then choose a point near one pole—typically the north pole—and place the compass so that its needle aligns with the magnetic field at that location. Mark a small dot at the tip of the needle to represent this direction.
Next, carefully move the compass so the base of the needle rests on the dot you just marked. Once it's in place, mark another dot at the tip of the needle. Repeating this “move–mark” process traces a path that follows the magnetic field line between and around the poles. After plotting the dots from one pole to another, remove the compass and join them with a smooth curve to reveal one continuous field line.
Magnetic Field Between Two Magnets
When sketching magnetic field lines note the following:
Field Direction: The lines emerge from the North pole and curve around to enter the South pole, consistent with the conventional direction of magnetic field lines. Magnetic field lines never cross each other.
Field Density: The field lines are denser near the poles, indicating that the magnetic field strength is strongest at the ends of the magnet. As the distance from the magnet increases, the density of the lines decreases, showing that the field weakens with distance.
Closed Loops: The lines form continuous closed loops, traveling inside the magnet from South back to North. Although iron filings cannot show the internal field clearly, we know from theory that the field continues through the interior of the magnet.
Symmetry: The field pattern is mostly symmetrical about the central axis of the magnet, showing the balanced distribution of magnetic force around the poles.
The following are three examples of magnetic field patterns:
