KCET · Physics · Magnetic Effects of Current
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
Answer & Solution
Correct Answer
(C) zero at any point inside the pipe
Step-by-step Solution
Detailed explanation
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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