Question

A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

• A. uniform throughout the pipe but not zero
• B. zero only along the axis of the pipe
• C. zero at any point inside the pipe
• D. maximum at the centre and minimum at the edge

Hint:

Inside a hollow conductor, the magnetic field is always zero.

Answer 1

The Correct Option is C

Step 1: Formula
According to Ampere's circuital law, $\oint B \cdot dl = \mu_0 I$.
Step 2: Internal Point
For any point inside the pipe ($r<R$), the current enclosed by the Amperian loop is zero.
Step 3: Calculation
$B_{internal} = \frac{\mu_0(0)}{2\pi r} = 0$.
Final Answer: (c)