Question : If a long hollow copper pipe carries a current, then produced magnetic field will be
a) both inside and outside the pipe
b) outside the pipe only
c) inside the pipe only
d) neither inside nor outside the pipe.
Doubt by Trishna
Solution :
From your Physics Classes, you can recall that we have calculated the magnetic field due to an infinitely long straight current carrying wire by using Ampere's circuital law.
As per Ampere's circuital law, the line integral of the magnetic field equals to µ₀ times the total current enclosed by the amperian loop.
So, if the total current passing through the amperian loop is zero, then line integral of the magnetic field is zero, and as a result, magnetic field (B) will also be zero.
Now, in the case of a long hollow copper pipe carrying a current, at any point outside the hollow copper pipe, there will be total current enclosed by the amperian loop, so it's line integral of the magnetic field will not be zero. As a result, there will be a magnetic field at any point outside the pipe.
But at any point inside the hollow copper pipe, zero current will be enclosed inside the amperian loop, so the line integral of the magnetic field will be zero. Hence, the value of the magnetic field at any point inside the hollow copper pipe will be zero.
Hence, b) outside the pipe only will be the correct option.
