at a point P a distance R = 10 mm above
its centerline?
Problem: A long, thin strip of copper (a = 8 mm wide) carries a current of
i = 80 A as shown.
What is the magnetic field at a point P a distance R = 10 mm above
its centerline?
Treat as sum of infinitely long, parallel wires each of width dx and carrying a current
Recall that the magnetic field a distance r from a long, straight wire carrying a current I is given by
As 
the field in the present case can have only 
and 
conponents.
The component of at P due to the bit of current flowing
at a distance x from the 
- plane is
where 
and
.
Thus,
and
Now, the integrand is an odd function of the variable of integration and the
range of integration is symmetric about the origin.
Hence, this integral gives 0 so only the component of
survives:
