A gravitational field has no sources, it has sinks at masses, and it has neither elsewhere, gravitational field lines come from infinity and end at masses.
![magnetic fieldlines magnetic fieldlines](https://i.ytimg.com/vi/JeSYcXFVGXE/maxresdefault.jpg)
For example, Gauss's law states that an electric field has sources at positive charges, sinks at negative charges, and neither elsewhere, so electric field lines start at positive charges and end at negative charges. the case of a force field of a radial harmonic. In physics, drawings of field lines are mainly useful in cases where the sources and sinks, if any, have a physical meaning, as opposed to e.g. In fields which are divergenceless ( solenoidal), such as magnetic fields, field lines have no endpoints they are either closed loops or are endless. For example, electric field lines begin on positive charges and end on negative charges. In vector fields which have nonzero divergence, field lines begin on points of positive divergence ( sources) and end on points of negative divergence ( sinks), or extend to infinity. Areas in which neighboring field lines are converging (getting closer together) indicates that the field is getting stronger in that direction.
![magnetic fieldlines magnetic fieldlines](https://qmagnets.com/wp-content/uploads/magnetic-field-lines-magnet.png)
Then the density of field lines (number of field lines per unit perpendicular area) at any location is proportional to the magnitude of the vector field at that point. In order to also depict the magnitude of the field, field line diagrams are often drawn so that each line represents the same quantity of flux. A field line diagram is necessarily an incomplete description of a vector field, since it gives no information about the field between the drawn field lines, and the choice of how many and which lines to show determines how much useful information the diagram gives.Īn individual field line shows the direction of the vector field but not the magnitude. Therefore which field lines are shown is a choice made by the person or computer program which draws the diagram, and a single vector field may be depicted by different sets of field lines.
![magnetic fieldlines magnetic fieldlines](https://mammothmemory.net/images/user/base/Physics/magnets/magnet-16-v2.7bf2e6b.jpg)
Since there are an infinite number of points in any region, an infinite number of field lines can be drawn but only a limited number can be shown on a field line diagram. Points where the field is zero or infinite have no field line through them, since direction cannot be defined there, but can be the endpoints of field lines. Since at each point where it is nonzero and finite the vector field has a unique direction, field lines can never intersect, so there is exactly one field line passing through each point at which the vector field is nonzero and finite. two-dimensional fields the field lines are plane curves, and most field line diagrams are of this type. A field line is usually shown as a directed line segment, with an arrow indicating the direction of the vector field.
![magnetic fieldlines magnetic fieldlines](http://2.bp.blogspot.com/-EXRFWisetRM/Uk7kho0fH4I/AAAAAAAADA8/j9t43MtLGXY/s1600/Magnetic+Field+Lines-04.png)
A field line for that vector field may be constructed by starting at a point and tracing a line through space that follows the direction of the vector field, by making the field line tangent to the field vector at each point. The figure at right shows the electric field lines of two equal charges of opposite sign.Ī vector field defines a direction and magnitude at each point in space. The figure at left shows the electric field lines of two equal positive charges.