What makes magnetic fields?

Question

i need to know the answer to this question its for a physics benchmark and the answer doesn't have to be very detailed 

 

Answer 1

The simplest answer is that a moving electrical charge creates a magnetic field.

 

Another question, though, is why.  You know that an electrical charge creates an electric field, which exerts a force on other electric charges.  It turns out, though, that when the laws of the Theory of Relativity are applied to the motion of an electric charge, you find that an additional force is present.  The simplest way to explain this is to say that the length contraction resulting from the motion of the charge makes the density of the charge appear to be greater, which results in an increase in the force felt by other charges.  When the math is done to figure out the exact effect produced by the motion of the charge, it turns out that the results agree exactly to the observed laws for magnetic fields.