Question

A long, straight, hollow conductor (tube) carrying a current has two sections A and C of unequal cross-sections joined by a conical section B. 1, 2 and 3 are points on a line parallel to the axis of the conductor. The magnetic fields at 1, 2 and 3 have magnitudes B₁, B₂ and B₃. 

(a) B₁ = B₂ = B₃ 

(b) B₁ = B₂ ≠ B₃

(c) B₁ < B₂ < B₃ 

(d) B₂ cannot be found unless the dimensions of the section B are known.

Answer 1

Correct Answer is: (a) B₁ = B₂ = B₃ 

To find the magnetic field outside a thick conductor, the current may be assumed to flow along the axis. As points 1, 2, 3 are equidistant from the axis, B₁ = B₂ = B₃.