Question

If long hollow copper pipe carries a direct current, the magnetic field associated with the current will be:

• A. only inside the pipe
• B. only outside the pipe
• C. neither inside nor outside the pipe
• D. both inside and outside the pipe

Answer 1

Answer: (B)

only outside the pipe

According to Ampere's law $\int \overrightarrow{B}\bullet \overrightarrow{d}l={\mu }_{0}i$
To any closed path inside pipe, there will be no current enclosed.

So B inside pipe is zero.

Only, there would be field outside the pipe.