![]() For example, the field direction is tangent to the line at any point in space. (Consider the direction of the field at such a point.)Ģ: List the ways in which magnetic field lines and electric field lines are similar. Field strength is proportional to the line density.ġ: Explain why the magnetic field would not be unique (that is, not have a single value) at a point in space where magnetic field lines might cross.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.The properties of magnetic field lines can be summarized by these rules: We use magnetic field lines to represent the field (the lines are a pictorial tool, not a physical entity in and of themselves). Gravitational fields map gravitational forces, electric fields map electrical forces, and magnetic fields map magnetic forces.Įxtensive exploration of magnetic fields has revealed a number of hard-and-fast rules. ![]() The field represents the object generating it. Note that the symbols used for the field pointing inward (like the tail of an arrow) and the field pointing outward (like the tip of an arrow).Ī field is a way of mapping forces surrounding any object that can act on another object at a distance without apparent physical connection. (c) When the wire is in the plane of the paper, the field is perpendicular to the paper. (b) A long and straight wire creates a field with magnetic field lines forming circular loops. (a) The magnetic field of a circular current loop is similar to that of a bar magnet. Small compasses could be used to map the fields shown here. 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. The magnetic field is traditionally called the B-field. As shown in Figure 1, the direction of magnetic field lines is defined to be the direction in which the north end of a compass needle points. The pictorial representation of magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Since magnetic forces act at a distance, we define a magnetic field to represent magnetic forces. His ability to think deeply and clearly about action at a distance, particularly for gravitational, electric, and magnetic forces, later enabled him to create his revolutionary theory of relativity.
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