Q. 6

In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero
A. outside the cable

B. inside the inner conductor

C. inside the outer conductor

D. in between the two conductors


Answer :


According to Ampere’s Law:
Where,

B is the magnetic field,


dl is the current element,


μ0 is the permeability of free space


i is the current flowing in the conductor



Magnetic field outside the cable: B = BI+BO
BI and BO are the magnetic field of the inner conductor and outer cable respectively.
Due to wire,
R is the radius of the wire.


Thus, option (A) is the correct option.


Magnetic field inside the inner conductor:


B. dl =μo I (I=0(inside the wire))


Magnetic field between the two conductors and inside the outer conductor.


B. dl =μo I


On integrating the length element over the complete loop, we get dl= 2π r


B.2π r=μo I


On solving the above equation for B, we get



Thus, option A and B is the correct option.

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