Electrical Engineering ⇒ Topic : Laws of magnetic force

Laws of Magnetic Force

Charles Coulomb, a French scientist observed that when two **isolated poles are placed near each other, they experience a force. He performed a number of experiments to study the nature and magnitude of force between the magnetic poles. He summed up his conclusions into two laws, known as Coulomb's laws of magnetic force. These laws give us the magnitude and nature of magnetic force between two magnetic poles

                                                                              figure (a)

Like poles repel each other while unlike poles attract each other

The force between two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of distance between their centres.

Consider two poles of magnetic strength m₁ and m₂ placed at a distance d apart in a medium as shown in Fig. (a). According to Coulomb's laws, the force between the two poles is given by

where K is a constant whose value depends upon the sun-ounding medium and the system of units employed. In SI units, force is measured in newtons, pole strength in *weber, distance in metres and the value of K is given by

Unit of pole strength. By unit pole strength we mean 1 weber. It can be defined from Coulomb's laws of magnetic force. Suppose two equal point poles placed 1 m apart in air exert a force of 62800 newtons i.e.

Hence a pole of unit strength (i.e. 1 Wb) is that pole which when placed in air 1 m from an identical pole, repels it with a force of 62800 newtons.

where d is a unit vector to indicate the direction of d.

LAWS 0F MAGNETIC FORCE

Coulomb, through his experiments found that the force between two magnetic poles placed in a medium is

1. directly proportional to their pole strengths (m₁,m₂ )
2. inversely proportional to the square of the distance (d) between them, and
3. inversely proportional to the absolute  permeability (μ) of the surrounding medium,

    i.e