Q. 55.0( 1 Vote )

A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field.
A. increases linearly from the axis to the surface

B. is constant inside the tube

C. is zero at the axis

D. is zero just outside the tube


Answer :


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.

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