A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field.


By Ampere’s Law ,
Here, dl is the current element, B is the magnetic field, μ0 is the permeability of free space and i is the current flowing.
We know that , magnetic field due to a circular wire is given
R is the radius of the wire.
Consider a Hollow tube as the series of circular wires.
Inside the tube at a point, r<R
Current inside the hollow tube is zero: iinside = 0

Hence , the magnetic field is constant inside the hollow tube.
Now, at the axis, R=0.

Therefore, zero current is enclosed.
Hence, B=0.
Thus, options (B) and (C) are the correct options.

1