A magnetic field is the area of
influence exerted by a magnetic force. This field is normally focused along two
poles. These poles are usually designated as north and south. However these
directions are not the only two that a magnetic field can have. Most magnetic
objects are composed of many small fields called domains. Here are some basic
concepts of a magnetic field. The first real study of magnetism started during
the 1600s and we are still trying to understand how the magnetic field works
First a magnetic field can not be
divided. A magnetic field will always be dipole which means it will have two
poles. If you divide a magnet you will only get a smaller magnet with the same
two poles. It will only change in its strength. If small enough a magnetic
field can be turned around in its orientation by a larger magnetic filed. This
is the reason why the domains in a ferromagnetic metal rarely orient in the same
direction before being magnetized.
Second a magnetic field is the
result of electric currents. An electric current is an electric charge moving
in a defined path. This movement is what creates magnetic fields. The current
can create a magnetic field as large as the Sun's magnetosphere and as small as
the domain of an atom. The important thing to know is that one is the companion
of the other. Without an electric field you can’t have a magnetic field.
Why does it have to be a moving charge?
You already know the answer. Have you ever taken two magnetic and try to and they to put them together, if you have two opposite ends the magnets are attracted, the same ends an there attracted. But what does this have to do with this situation?
If you remember, magnetic fields are created by moving charges. So in qV x B the qV is a current, a moving charge, so the equation is nothing more then a mathematical expression of of two magnets interacting.
More about Magnetic Fields
Magnetic fields are produced by electric currents, which can be macroscopic currents in wires, or microscopic currents associated with electrons in atomic orbits.
From the force relationship above it can be deduced that the units of magnetic field are Newton seconds /(Coulomb meter) or Newtons per Ampere meter. This unit is named the Tesla. It is a large unit, and the smaller unit Gauss is used for small fields like the Earth's magnetic field. A Tesla is 10,000 Gauss. The Earth's magnetic field at the surface is on the order of half a Gauss.
