The
illustration at right shows the magnetic field set up by a moving charge q
with a velocity v (click on the illustration for a VRML model of
the moving charge). Now, moving charges is basically current, right? So,
let's find the magnetic field set up by a current of i. We will
break up the current of this imaginary wire into current elements of i
ds. However, we should note that this current element is a vector
quantity, so we need to take that into account by using an angle q. So, we
have the magnetic field of the current element to be:
(Equation 6-63)
m0 is a constant called the permeability constant and is equal to 4p x 10-7 T m/A. Sometimes, the value of m0/4p is just refered to as a constant k', which has the value of 10-7 T m/A. Anyway, continuing with our discussion, if you write Equation 6-63 in a more general term, using a vector cap over the r to indicate direction instead of using sin q, you get:
(Equation 6-64)
This is called the Biot and Savart Law (incidently, the names rhyme with "Leo and bazaar"; don't ask us why).
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