![]() The field is tangent to the magnetic field line.Magnetic fields can be pictorially represented by magnetic field lines, the properties of which are as follows:.If magnetic monopoles existed, then magnetic field lines would begin and end on them. It is a distinct difference from electric field lines, which begin and end on the positive and negative charges. The last property is related to the fact that the north and south poles cannot be separated. They go from the north pole to the south pole. Magnetic field lines are continuous, forming closed loops without beginning or end.Magnetic field lines can never cross, meaning that the field is unique at any point in space.It is exactly proportional to the number of lines per unit area perpendicular to the lines (called the areal density). The strength of the field is proportional to the closeness of the lines.A small compass will point in the direction of the field line. The direction of the magnetic field is tangent to the field line at any point in space.Note the symbols used for field into and out of the paper. A small compass placed in these fields will align itself parallel to the field line at its location, with its north pole pointing in the direction of B. In both cases, the fields represent only the object creating them and not the probe testing them.) Figure 2 shows how the magnetic field appears for a current loop and a long straight wire, as could be explored with small compasses. ![]() (This is analogous to the way we tested electric fields with a small test charge. Small compasses used to test a magnetic field will not disturb it. (c) If the interior of the magnet could be probed, the field lines would be found to form continuous closed loops. The strength of the field is proportional to the closeness (or density) of the lines. (Recall that the Earth’s north magnetic pole is really a south pole in terms of definitions of poles on a bar magnet.) (b) Connecting the arrows gives continuous magnetic field lines. (a) If small compasses are used to map the magnetic field around a bar magnet, they will point in the directions shown: away from the north pole of the magnet, toward the south pole of the magnet. ![]() Magnetic field lines are defined to have the direction that a small compass points when placed at a location.
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