There are the following laws:
(i) First law. Like poles repel each other; unlike poles attract each other.
(ii) Second law. The force exerted between two magnetic poles in proportional to the product of their pole strengths and is inversely proportional to the square of distance between them.
These can be expressed by the formula,
Where ml and m2 are their pole strengths and d as the distance between them and K is a constant the value of which depends upon the nature of the medium in which the poles are placed.
In S.I. system of units, K
Where permeability of the vacuum and is the relative permeability of the medium with respect to the permeability in free space or vacuum.
Unit pole
Let ml = m2 pole strength, d the distance as 1m., and
force exerted as
Hence a unit magnetic pole is defined as that pole which when placed at one metre apart from a similar pole exert a attractive or repulsive force of 1/4
Or
A unit pole is also defined (in CGS system of units) if, when placed at a distance of one cm, from a similar pole, Causes a repulsive or attractive force of one dyne.
