If a long hollow copper pipe carries a current, then

Home » Electricity and Magnetism » Moving Charges and Magnetism » Question

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

1. inside the pipe only
2. outside the pipe only
3. both inside and outside the pipe
4. no where

Correct Option: B

Inside a hollow pipe carrying current, the magnetic field is zero, since according to Ampere’s law, B_i. 2πr = µ₀ × 0 ⇒ B_i = 0.
But for external points, the current behaves as if it was concentrated at the axis only; so, outside,

B₁ =	μ₀i
	2πr

. Thus, the magnetic field is produced outside the pipe only.