Having gone through the history of the development of magnetism, we may now 
begin our quantitative analysis of magnetic fields and forces. The study of 
magnetic fields is quite complicated, much more complicated than that of 
electric fields, and requires more effort to fully 
describe. The largest challenge regarding magnetic fields is the absence of 
magnetic charge. With electric fields, we were able to describe the field 
created in terms of a single charge, then generalize for a number of charges. 
With magnetic field, there are multiple sources of fields, not a single 
indivisible quantity, such as charge. 
As such, we must begin 
by defining the forces felt by moving particles in magnetic fields without 
defining the source of the field.  Don't worry in this section if you find the 
situations a little hard to grasp conceptually. We are working with an 
incomplete picture of magnetic fields, something that will be remedied in the 
next SparkNote. After 
defining forces felt by moving particles, we generalize our concepts for many 
moving charges 
(currents).
This SparkNote puts in place the first piece of the puzzle of magnetic fields.  From 
the definitions we here derive we will be able to move on to describe not 
only the forces from magnetic fields, buy the sources of the fields.