The presence of a magnetic field is detected by the forces of attraction or repulsion which it exerts on similar objects within its range. It is characterized by the presence of magnetic lines, which seem to be non-intersecting and oriented from one pole of the magnet to the other. It is a vector quantity, one which is described by both magnitude and direction. The magnetic lines are not physical lines, but imaginary ones, which help in the understanding of the field. In short, the orientation and the working range of the field is represented and more easily understood by representing it in the form of these lines.
How do Magnetic Fields Work?
Magnetic field lines represent the locus of all the points which lie within a vector field and are characterized by a precise origin point in that field. These lines have a common start and end point, but never intersect each other. The shape can be roughly thought to be similar to that of a rugby ball. If lines were drawn from a point at the tip of one end of this ball to the other, such that no two lines intersect, they give an idea about how the field is oriented and the shape of its area of influence.
In other words, these lines give the three dimensional representation of a magnetic field. If a narrow strip of magnet is suspended freely in this field, it will be seen to align itself in the direction of the lines. These lines are more spread out when the field is weak, and more concentrated or dense in the region where the field is strong. Consider a small strip of bar magnet which has a certain region of influence. The lines, representing its area of influence, would align themselves from the north pole to the south pole. These lines would be spread out away from poles and start converging as they approach the other pole. These lines are spread out the furthest, at the center, as if bulging out.
This shows that the strength of a magnet is the maximum at the poles and the least as we move away from the poles. The same is true in case of the Earth's magnetic field and its orientation. The pioneer in the field of electricity and magnetism, Michael Faraday, was the one who first stated the presence of these lines and called them, 'lines of force'.
The presence of a magnetic field and the area worked upon by its influence has been a tremendous find of the modern times. The presence and detection of magnetic energy, as represented by the lines, led to a huge set of revelations. For instance, electromagnetism and research associated with phenomena like the waves, such as television, radio, microwaves, infrared, X-rays, ultra violet rays, is a result of developments in the area of magnetism. Certainly, it has proved to be a big boost for the advancement of various sciences.