Line of force
From Wikipedia, the free encyclopedia
Line of force or line of flux , usually taken in the context of electromagnetism, is the curve whose tangent gives the direction of the field at that point. As a result, it also runs perpendicular to the equipotential lines in the conventional direction from higher to lower potential.
A tube of force, also called a tube of electrostatic induction or field tube, are the lines of electric force which moves so that its beginning traces a closed curve on a positive surface, its end will trace a corresponding closed curve on the negative surface, and the line of force itself will generate an inductive tubular surface. Such a tube is called a "Solenoid". There is a pressure at right angles to a tube of force of one half the product of the dielectric and magnetic density. If through the growth of a field the tubes of force are spread sideways or in width there is a magnetic reaction to that growth in intensity of electric current. However, if a tube of force is caused to move endwise there is little or no drag to limit velocity. Tubes of force are absorbed by bodies imparting momentum and gravitational mass.
[edit] Common Misconceptions
In the context of electromagnetism it is often assumed that lines of force have physical existence, and even that they are discrete and therefore, at least in principle, countable.
This probably derives from a misunderstanding of the experiment where iron filings are sprinked on a piece of paper over a magnet and form discrete lines. The reason they form discrete lines is not that they are aligning with pre-existing discrete magnetic lines of force, but that the lines of filings can only be one iron particle wide and as soon as one line forms it repels others. So the number of lines seen and their closeness depends on the size of the iron particles.
To make matters worse, there was a unit of magnetic flux in the obsolete CGS system called the "line" (later called the maxwell) equal to 10^-8 webers.
When a symmetric magnet is rotated about its axis of symmetry, people ask whether the lines of force rotate with the magnet or not. The question is meaningless, as magnetic flux is not made up of discrete lines. This is like asking, of a uniformly coloured disk, whether the colour (i.e. the property, not the coating) rotates with the disk. This misunderstanding is one that gives rise to the so called Faraday Paradox.
