Magnetic interactions and magnetic poles


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        The magnetic field is a region in which a particle with magnetic properties experiences a force, and in which a moving charge experiences a force.

The magnets with two poles can only exist. Any magnet can have two poles as north and south. And the magnets can be of two types, one being permanent and the other being electromagnet. Permanent magnets are usually made of iron cobalt or nickel alloys. In case of electromagnets, the magnetic fields are produced by electric currents. The sources of magnetic fields or the magnets have always two poles, one being north and the other being south. The lines of force in case of magnetic fields travel from North Pole to South Pole:

The interaction of magnetic field with charge leads to many practical applications. The interaction of magnetic field with moving charge leads to various applications like in cyclotron, mass spectrometer, electric motor, galvanometer, voltmeter, ammeter, loudspeaker, generator, microphone, and Hall Effect etc.

The magnitude of the magnetic force (FB) exerted on a charged particle is proportional to the charge (q) contained in it and the velocity (v) of the moving charged particle. The magnitude and direction of FB depend upon the velocity of the particle and on the magnitude and direction of the magnetic field (B). When the charged particle moves parallel to the magnetic field vector, the magnetic force acting on the particle is zero. When the particle’s velocity vector makes an angle θ≠0 with the magnetic field, the magnetic force acts in a direction perpendicular to both v and B; that is FB is perpendicular to the plane formed by v and B. It should be noted that the magnetic force exerted on a positive charge is in the direction opposite to the direction of the magnetic force exerted on a negative charge, which moves in the same direction as that of the positive charge. And the magnitude of the magnetic force exerted on the moving particle is proportional to sinθ, where θ is the angle made by the particle’s velocity vector with the direction of B. Thus, the magnetic force exerted on a moving charge can be written as:

The direction of FB is in the direction of v × B if q is positive. This equation defines the magnetic field in terms of the force acting on a moving charged particle.