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A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is
Options:
Solution:
1806 Upvotes
Verified Answer
The correct answer is:
zero at any point inside the pipe
Required arrangement is shown in figure. According to Ampere's circuital law.
For an internal point, $r < R$
$$
\mathrm{B}_{\text {internal }}=\frac{\mu_{0}(0)}{2 \pi \mathrm{r}}=0
$$
For a point on the pipe, $r=R$
$$
B=\frac{\mu_{0} I}{2 \pi r}
$$
For an external point, $r < R$
$$
\mathrm{B}_{\text {external }}=\frac{\mu_{0} \mathrm{I}}{2 \pi \mathrm{r}}
$$
Therefore, option (c) is correct.
For an internal point, $r < R$
$$
\mathrm{B}_{\text {internal }}=\frac{\mu_{0}(0)}{2 \pi \mathrm{r}}=0
$$
For a point on the pipe, $r=R$
$$
B=\frac{\mu_{0} I}{2 \pi r}
$$
For an external point, $r < R$
$$
\mathrm{B}_{\text {external }}=\frac{\mu_{0} \mathrm{I}}{2 \pi \mathrm{r}}
$$
Therefore, option (c) is correct.
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