Q. 6

# In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zeroA. outside the cableB. inside the inner conductorC. inside the outer conductorD. in between the two conductors

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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