A current I flows along the length of an infinitely long, straight, thin walled pipe. Then (a) the magnetic field at all points inside the pipe is the same, but not zero (b) the magnetic field is zero only on the axis of the pipe (c) the magnetic field is different at different points inside the pipe (d) the magnetic field at any point inside the pipe is zero

Answer: (d). Take a circular Amperian loop inside the pipe, coaxial with it. All current flows on the wall, so Ienc = 0 ⇒ B (2π r) = 0. B = 0 at every point inside. So the answer is (d).

A current I flows along the length of an infinitely long, straight… | JEE Main 2007 (AIEEE)

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Ampere's Law, Cylinders, Solenoid & Toroid

A current $I$ flows along the length of an infinitely long, straight, thin walled pipe. Then

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Answer: (d)

Take a circular Amperian loop inside the pipe, coaxial with it.
All current flows on the wall, so $I_{enc} = 0 \Rightarrow B (2\pi r) = 0$ .
$B = 0$ at every point inside.
So the answer is (d).

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