Question

In a co-axial straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero. 

(1) inside the outer conductor 

(2) in between the two conductors 

(3) outside the cable 

(4) inside the inner conductor

Answer 1

Correct option is : (3) outside the cable

\(\oint \vec{B} \cdot {d} \vec{\ell}=\mu_{0} \mathrm{i}_{\text {enc }}=0\)

\(\therefore \mathrm\ {B}=0\) outside the cable