A coaxial cable having radius "a" of inner wire and inner and outer radii "b" and "c" respectively of the outer shell carries equal and opposite currents of magnitude i on the inner and outer conductors as shown. What is the magnitude of the magnetic induction at point P of the cable at a distance r (b < r < c) from the axis?

Question

G1 Physics · Accepted Answer

For b<r<c, the enclosed return current in the outer shell is I(r²-b²)/(c²-b²). Thus I enclosed=I[1-(r²-b²)/(c²-b²)]=I(c²-r²)/(c²-b²). Hence B=μ₀I(c²-r²)/[2πr(c²-b²)], option D.