JEE MAIN - Physics (2007 - No. 12)
A current $$I$$ flows along the length of an infinitely long, straight, thin walled pipe. Then
the magnetic field at all points inside the pipe is the same, but not zero
the magnetic field is zero only on the axis of the pipe
the magnetic field is different at different points inside the pipe
the magnetic field at any point inside the pipe is zero
Vysvetlenie
There is no current inside the pipe. Therefore
$$\oint {\overline B .\overline {d\ell } } = {\mu _0}I$$
$$I=0$$
$$\therefore$$ $$B=0$$
$$\oint {\overline B .\overline {d\ell } } = {\mu _0}I$$
$$I=0$$
$$\therefore$$ $$B=0$$