\fPart A at points outside the central, solid conductor but inside the tube Part B at points outside the tubeA solid conductor with radius a is supported by insulating disks on the axis of a conducting tube with inner radius b and outer radius c ((Figure 1)). The central conductor and tube carry currents I1 and I2 correspondingly in the same direction. The currents are distributed uniformly over the cross sections of each conductor. Derive an expression for the magnitude of the magnetic field