Magnetic Field

Magnetic Field

Lines of Magnetic field (Magnetic lines of force)    

Definition : A magnetic line of force, is a line straight or curved, in the magnetic field of a magnetic pole of magnetic dipole, such that the tangent at any point of this line gives the direction of the magnetic field at that point.

Properties of Magnetic Lines of Force

These have following properties :

They are always nearly normal to the surface of magnet at every point.


They start from a north (positive) pole and end at a south (negative) pole.

Two lines of force do not intersect each other.

They tend to contract longitudinally (longitudinal contraction).

They tend to expand laterally (lateral repulsion) so as to exert lateral pressure on neighboring lines.

(The above two properties are similar to that of a stretched rubber band).

The number of magnetic lines of force passing normally per unit area about a point, gives the intensity of the magnetic field at the point.

Earth’s Magnetic Field

Earth Magnetism : Earth behaves as a huge magnet (or a giant solenoid). The source of this huge magnetism is given as the molten charged metallic fluid giving rise to a current flowing inside the core of the earth. This core has a radius of about 3500 km (earth’s radius is 6400 km).

Some Associated Terms

  1. South Magnetic Pole (S) : It is near north geographical pole N.
  2. North Magnetic Pole (N) : It is near south geographical pole S.
Earth Magnetic field
Earth Magnetic field