Home » BASIC FUNDA » MAGNETIC FIELD & FORCE

WHAT IS MAGNETISM?
Magnetism is nothing but a force produced by magnetic fields, which is caused by motion of electric charges.
It means, magnetism is a force of attraction or repulsion, acts at a distance.
The movement of electrically charged particles maybe from electric current through a conductor, charged particles through space, or motion of electron in an atomic orbital and also the rotation of electron about its own axis, which is called electron spin.
NOW WHAT IS MAGNETIC FIELD?
Magnetic fields are produced by electrically charged particles either by moving or spinning. These are imaginary lines of flux flow from one end of the object to the other. Conventionally one end of the object called N or North Pole as related to earths north and the other called S or South Pole related to earths south. Magnetic fluxes are assumed moving from N to S pole.n, that means all particles such as electrons can have own magnetic field.
When an object has a great magnetic field, it is called magnet.

MAGNETIC FORCE: The magnetic field which is created by motion of electric charges creates force on other object inside the magnetic field. This force is known as magnetism.
Within the magnetic field, when two magnetic objects are placed nearer to each other, the unlike poles attract each other called attraction force and like poles repeal each other called repulsion force.
When a magnetic field applied to electric current in a conductor, the force on the moving electric charge is perpendicular to the direction of the charge and also perpendicular to the direction of the magnetic field. It is the vector combination of two forces. This force is called LORENTZ force.
The relationship between the force and charge is

F = q V B sinθ
Where F = Force in Newton.
q = charge in Coulomb.
V = velocity of positive charge meter/second.
B = strength of magnetic field in Tesla.
Sinθ = sin angle between V and B.
So, force on electric charge depends on velocity of charge particle, the strength of magnetic field and the angle between the directions of particle.
So, if V = 0, force is 0, also if moving particle directions is parallel to magnetic field, the force,F =0.

LAWS OF MAGNETIC FORCE: This law expresses the magnetic force between two isolated point poles. Though practically it is impossible to get an isolated pole because magnetic pole is always exist in pairs even in smallest particles. So isolated pole thinking is conceptual.
Now we consider a long magnet and its N & S pole as unit pole.
This law states that the force between these poles in a medium is (i) directly proportional to their pole strengths.
(ii) Inversely proportional to the square of the distance between them and
(iii) Inversely proportional to the absolute permeability of the surrounding medium.

If m1 and m2 represent the magnetic strength of N and S pole respectively and r is the distance between them, then the force F is given by
F∞ m1m2/µr2 or F=K m1 m2/r2
Where µ is the absolute permeability of the surrounding medium.
K is constant and the value is 1/4π (in S.I system).
So, F= m1m2/4πµr2 Newton or, F=K m1 m2/4πµ0µrr2 (in medium).
If m1=m2=m=1; r=1 meter, then F= 1/4πµ0 Newton.
Now in a vacuum, an unit magnetic pole definition is that with a distance of 1 meter like poles repeal each other with a force of 1/4πµ0 Newton and 1/4πµ0µr Newton in a medium.Coulomb was first to determine this and known as coulombs law.