|line of force|
|an imaginary line representing a field of force, such as an electric or magnetic field, such that the tangent at any point is the direction of the field vector at that point|
|line of force
A line used to indicate the direction of a field, especially an electric or magnetic field, at various points in space. The tangent of a line of force at each point indicates the orientation of the field at that point. Arrows are usually used to indicate the direction of the force. See Note at magnetism.