JEE Main · 2024 · 05 Apr 2024 · Shift 1 · Magnetic Effects of Current

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

(A)inside the outer conductor
(B)in between the two conductors
(C)outside the cable✓ Correct
(D)inside the inner conductor

Answer: (C)

Solution

By Ampere's law

\oint B \cdot d l = μ_{0} I_{e n c}

. Outside the whole cable the enclosed current is

I + (- I) = 0

(equal and opposite currents), so

B = 0

outside the cable. Between the conductors and inside the outer conductor the enclosed current is non-zero, so the field there is not zero.

JEE Main · 2024 · 05 Apr 2024 · Shift 1 · Single correct option

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