If a long hollow copper pipe carries a current, then magnetic field is produced

(a) Inside the pipe only

(b) Outside the pipe only

(c) Both inside and outside the pipe

(b) No where

(b)

Inside a hollow pipe carrying current, the magnetic field is zero, [since according to Ampere''s law, B_i. 2pr = m₀ × 0 Þ B_i = 0.

But for external points, the current behaves as if it was concentrated at the axis only; so, outside,

B₀ = ⁱ. Thus, the magnetic field is produced outside the pipe only.