An infinitely long, straight conductor consists of an inner cylindrical conductor of radius R which carries a uniform current I0. This conductor is surrounded by a second, coaxial conductor of inner radius R and outer radius 2R. Through this outer conductor flows a uniform current of 2I0, with a direction that is opposite to the one in the central conductor.
Calculate the magnetic field strength B for the following distances from the center of the conductor:
a. r> 2R
b. R< r<2R
c. r