JEE MAIN - Physics (2004 - No. 12)
A current $$i$$ ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is
$${{{\mu _0}} \over {4\pi }},{{2i} \over r}$$ tesla
zero
infinite
$${{2i} \over r}$$ tesla
Explanation
Using Ampere's law at a distance $$r$$ from axis, $$B$$ is same from symmetry.
$$\int {B.dl = {\mu _0}i} $$
i.e., $$B \times 2\pi r = {\mu _0}i$$
Here $$i$$ is zero, for $$r < R,$$ whereas $$R$$ is the radius
$$\therefore$$ $$B=0$$
$$\int {B.dl = {\mu _0}i} $$
i.e., $$B \times 2\pi r = {\mu _0}i$$
Here $$i$$ is zero, for $$r < R,$$ whereas $$R$$ is the radius
$$\therefore$$ $$B=0$$
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